Malarial Drug Delivery Systems: Advances in Treatment of Infectious Diseases 3031158474, 9783031158476

Citation preview

Ranjita Shegokar Yashwant Pathak   Editors

Malarial Drug Delivery Systems Advances in Treatment of Infectious Diseases

Malarial Drug Delivery Systems

Ranjita Shegokar  •  Yashwant Pathak Editors

Malarial Drug Delivery Systems Advances in Treatment of Infectious Diseases

Editors Ranjita Shegokar CapnoPharm GmbH Tübingen, Germany

Yashwant Pathak Taneja College of Pharmacy University of South Florida Florida, USA

ISBN 978-3-031-15847-6    ISBN 978-3-031-15848-3 (eBook) https://doi.org/10.1007/978-3-031-15848-3 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

An article published in the Washington Post of 2016 stirred an intense discussion between the public, scientific communities, and health authorities. How many diseases are precisely known to humankind? At the moment, scientist estimates the presence of more than 10,000 human diseases and only fewer available treatments that too for major diseases.1 In 2022, the scenario is not far different considering the deliberate speed of academic/industry research, economic up-downs, tougher regulatory policies, complex clinical trial setups, the impact of the Covid-19 pandemic in slowing processes, businesses, and changing world political dynamics and policies. The same question on “availability of effective treatment” is valid now and maybe even after next 2–3 decades. Diseases can be genetic or caused by environmental factors (mainly known as infectious diseases). Human infectious diseases are typically classified according to the source of infection as anthroponoses (human–human transmission), zoonoses (animal–human transmission), and sapronoses (abiotic decaying substrate— human). These infectious diseases contribute to the enormous financial burden on the country’s economy. By 2001, around 1415 species of organisms had been recorded known to be pathogenic to humans, mainly comprised of bacteria, viruses/ prions, fungi, protozoa, and helminths. This book is a trivial attempt to compile all possible and available information on etiology, pathology, current therapy options available for a wide spectrum of diseases, the role of drug delivery sciences, advances in new techniques, diagnostic tools, and new drug research of various infectious diseases. Total four volumes are compiled to accommodate vast available information. Volume 1—Malarial drug delivery systems (MDDS) Volume 2—Tubercular drug delivery systems (TDDS)  Are there really 10,000 diseases and just 500 ‘cures’?  – The Washington Post https://www. orpha.net/ 1

v

vi

Preface

Volume 3—Viral drug delivery systems (VDDS) Volume 4— Infectious disease drug delivery systems (IDDS)

Volume 1: MDDS Malaria is a disease caused by the parasite Plasmodium. The parasite spread to humans through the bites of infected mosquitoes causing high fever, nausea, vomiting, diarrhea, body pain, rapid heart rate, and shaking chills. Each year millions of people get infected by malaria, and many hundred-thousand people die. Some of the most significant risk areas include Sub-Saharan Africa, South and Southeast Asia, Pacific Islands, Central America, and Northern South America. The treatment of malaria mainly comprises the most common antimalarial drugs like chloroquine, primaquine, etc. In the case of drug resistance, artemisinin-based combination therapies (ACTs) are preferred. ACT is an amalgamation of two or more drugs that work against the malaria parasite using a different mechanism of action.

Volume 2: TDDS Tuberculosis (TB) is a potentially severe infectious disease that affects the lungs and, in some cases, the kidney, spine, and brain. Mycobacterium causes tuberculosis via air route. As a result, two TB-related scenarios are possible: latent TB infection (LTBI) and TB disease. If not treated properly, TB disease can be fatal. TB bacteria usually grow in the lungs (pulmonary TB). The typical test used to diagnose TB is the Mantoux tuberculin skin test (TST). The medications used to treat latent TB infection include Isoniazid, Rifapentine, and Rifampin. Classically, the patient may undergo several treatment regimens (1st/2nd /3rd line) recommended as per disease condition and health policy of that specific country. TB treatment can take 4, 6, or 9 months depending on the regimen.

Volume 3: VDDS Viruses are very tiny infectious germs, which cause infectious diseases such as the common cold, flu, and wart to severe illnesses such as HIV/AIDS, Ebola, and Covid-19 (which caused the recent pandemic where millions of people lost life). They invade living, normal cells and use those cells as host. Depending upon the type of virus, the target body cells are different. Virus infections and diseases are categorized under ten other groups, i.e., contagious, respiratory, gastrointestinal, exanthematous, hepatic, transmission, cutaneous, hemorrhagic, neurologic, and rest

Preface

vii

of the viruses not in these categories. All viruses have a protein coat and a core of genetic material, either RNA or DNA; unlike bacteria, viruses can't survive without a host. The diagnosis of viral diseases/infections can be performed by viral culture, serological tests, virus antigen detection, and viral nucleic acid or antibody detection. The treatment of viral diseases/infections depends on the type of viral infection. Antibiotics do not work for viral infections. FDA has already approved several antiviral medicines for the treatment of certain illnesses.

Volume 4: IDDS Each infectious disease has its specific signs and symptoms. Diagnosis of infectious diseases needs lab testing. Samples of body fluids, e.g., blood, urine, saliva, etc., can reveal evidence of the particular microbe that is causing the illness. While imaging, scans using X-rays, computerized tomography, and magnetic resonance imaging can help pinpoint disease states. Often, local tissue biopsies provide helpful information on the state of infection and adverse observations of disease (if any). This volume is focused on diagnosis, detection, disease models, the link between two or multiple infectious diseases, and vaccine development for the treatment of infectious diseases This book series compiles all the new treatment avenues that have been explored to treat malaria, tuberculosis, viral infections, and other infectious diseases like Ebola and hepatitis. This series covers various aspects of drug delivery advances for disease targeting, new drug molecules, analysis of currently ongoing clinical trials, vaccine development, and availability of disease models to evaluate drug performance. Dedicated chapters are included on herbal treatment opportunities for each disease. In addition, readers can refer to information on global disease health scenarios, cellular pathophysiology, and drug resistance, full coverage on polymeric nanoparticles, solid lipid nanoparticles, dendrimers, liposome, and micro/nanoemulsions as drug delivery carriers. Experts from all over the world have shared their knowledge to generate this one-­ stop resource. This book series is destined to fill the knowledge gap through information sharing and organized research compilation from the diverse expert area of pharma, medicine, clinical, chemist, and academics to fulfill following specific objectives: • • • • •

To discuss opportunities and challenges in the treatment of infectious diseases To enlist current efforts by researchers and experts To facilitate the insight and knowledge sharing To highlight innovative, cutting-edge micro and nanotechnology research To establish collaborations between academic scientists, industrial, and clinical researchers

viii

Preface

In summary, we are sure this book series will provide you great insights into drug delivery sciences (conventional, micro-nanomedicines, upcoming drug delivery trends) along with updates on clinical and chemical drug research for the treatment of infectious diseases. Tübingen, Germany Florida, USA

Ranjita Shegokar Yashwant Pathak

Contents

 Global Health and Malaria: Past and Present����������������������������������������������    1 Suryaveer Sankineni, Sarika Chauhan, Ranjita Shegokar, and Yashwant Pathak  Malaria: Cellular Understanding of Disease������������������������������������������������   17 Arnold Donkor Forkuo and Kofi Oduro Yeboah Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat Antimalarial Resistance����������������������������������������������������������������   43 Chirag A. Patel, Sonal Pande, Priya Shukla, Ketan Ranch, Moawia M. Al-Tabakha, and Sai H. S. Boddu  Malaria – Current Treatment Options����������������������������������������������������������   71 Dita Maria Virginia, Ranjita Shegokar, and Yashwant Pathak  Polymeric Nanoparticles in Malaria��������������������������������������������������������������   91 Himanshu Paliwal, Bhupendra G. Prajapati, Akshay Parihar, Geeta K. Patel, Prakash Kendre, Biswajit Basu, and Jayvadan K. Patel  Solid Lipid Nanoparticles in Malaria������������������������������������������������������������  113 Himanshu Paliwal, Bhupendra G. Prajapati, Akshay Parihar, Saikala Ganugula, Jayvadan K. Patel, and Mahavir Chougule Dendrimers in Malaria������������������������������������������������������������������������������������  139 Chaudhary Sunita, Khodakiya Akruti, Chaudhary Ankit, and Jayvadan K. Patel  Liposomal Drug Delivery in Malaria ������������������������������������������������������������  161 Hemanga Hazarika, Harshita Krishnatreyya, Bedanta Bhattacharjee, Damanbhalang Rynjah, Dharmajit Gogoi, Abdul Baquee Ahmed, and Kamaruz Zaman

ix

x

Contents

Potential of Micro-/Nanoemulsions as a Delivery Carrier to Treat Malaria ����������������������������������������������������������������������������������������������  187 Vaibhavi Srivastava, Shruti Srivastava, Neelu Singh, and Poonam Parashar  Nanosuspensions in Treatment of Malaria����������������������������������������������������  207 Kartik Hariharan, Harshit Barot, Jahanavi Patel, Mohit Shah, and Tejal Mehta  Alginate-Gelatin Nanoparticles in Malaria ��������������������������������������������������  233 Dasharath Patel, Sanjay Chauhan, Vikash Tiwari, Devashri Vadiya, and Jayvadan K. Patel Niosomes in Malaria����������������������������������������������������������������������������������������  253 Geeta K. Patel, Bhupendra Prajapati, and Yashawant Pathak  Surface-Modified Drug Delivery Systems in Malaria����������������������������������  279 Tayo Alex Adekiya, Pradeep Kumar, and Yahya E. Choonara Clinical Trials in Malaria��������������������������������������������������������������������������������  305 Neelutpal Gogoi and Md. Kamaruz Zaman  Potential of Herbal Drug Delivery in Treating Malaria ������������������������������  333 Aparoop Das, Kalyani Pathak, Manash Pratim Pathak, Riya Saikia, Urvashee Gogoi, and Niyati S. Acharya  Exploration on Metal Nanoparticles for Treatment of Malaria������������������  359 Anupam Sarma, Bhanu P. Sahu, and Malay K. Das Index������������������������������������������������������������������������������������������������������������������  393

Global Health and Malaria: Past and Present Suryaveer Sankineni, Sarika Chauhan, Ranjita Shegokar, and Yashwant Pathak

Abstract  Although malaria is a curable and preventable disease, it has wreaked havoc across the globe, affecting millions of people’s lives for decades since its inception. P. vivax and P. falciparum are the two most common species of malarial parasite. The global presence of malaria has pointed countless scientists and public health organizations in the direction of innovation. This comradery led to the discovery and worldwide distribution of drugs like artemisinin and tafenoquine along with numerous other antimalarial medications. The regions experiencing the worst health outcomes are sub-Saharan Africa and Northeast Asia. There was a decline in the sub-Saharan African region due to the successful implementation of various preventative methods, such as insecticide-treated nets (ITM). On the other hand, Northeast Asia is struggling to maintain its prevention standards as more counterfeit drug markets erupt. Hence, stringent drug regulations could prove beneficial in decreasing the presence of antibiotic resistance malaria against these counterfeit markets. The Middle East and Southern Asia have made great progress toward the elimination of malaria. It is important to note that these regions are also the least populous, making implementation and enforcement of preventative methods more manageable. Due to the emergence of COVID-19, nearly all global malaria programs have halted or rerouted their efforts and resources to face the pandemic. This sudden interruption in malaria prevention programs has pushed back the previous global eradication plans. Implementing a centralized database covering the global spread of diseases and drug use can be used to standardize current haphazard policies and local databases. A more unified oversight could streamline response strategies specific to each region optimizing malaria prevention.

S. Sankineni · S. Chauhan · Y. Pathak (*) Taneja College of Pharmacy, University of South Florida, Tampa, FL, USA R. Shegokar CapnoPharm GmbH, Tuebingen, Germany e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 R. Shegokar, Y. Pathak (eds.), Malarial Drug Delivery Systems, https://doi.org/10.1007/978-3-031-15848-3_1

1

2

S. Sankineni et al.

Keywords  Plasmodium · Malaria · Prevention · Health · Global · Antimalarial · Resistance

1 Introduction 1.1 What Is Plasmodium Malaria is known as one of the deadliest diseases in the world, despite significant global effort to reduce its transmission and decrease mortality rates. The disease is caused by the parasites of the genus Plasmodium (P.). These parasitic protozoa are transmitted to humans via female Anopheles mosquitoes that have also been infected. There are five known Plasmodium species that cause malaria in humans [1]. Two of the most important are P. falciparum and P. vivax. According to the World Health Organization in 2018, 99.7% of malaria cases in the African region, 50% of cases in the Southeast Asian region, 65% in the Western Pacific region, as well as 71% of cases in the Eastern Mediterranean region were caused by P. falciparum. This species is responsible for the most deaths from malaria across the globe. P. vivax is more central to the Americas as it accounts for 75% of malaria cases in the region [2]. The other human-infecting species include P. malariae, P. ovale, and P. knowlesi [3]. P. knowlesi, the final species of human infecting malaria, was first thought to only infect monkeys and apes (simian malaria species). Prior to its discovery, P. knowlesi was grouped with the cases of P. malariae. It was first discovered as a human-infecting malaria in Malaysian Borneo. Now, P. knowlesi is emerging as a potentially lethal parasite for malaria. The future of handling malaria globally lends itself to consistent research and development in specific preventions and methods of treatment [4]. After the female mosquito bites and transfers the plasmodium parasite, it enters into the bloodstream and to the liver, which becomes infected and inflamed as a result. The infection then proceeds to reenter the bloodstream where it now affects the red blood cells, where the parasites continue to multiply. Each cycle of multiplication, where blood cells burst releasing more parasites (48–72 h), the infected person will experience fevers, chills, and increased perspiration. In both P. vivax and P. ovale, the parasite can remain in the liver for several years before the patient experiences symptoms [1]. P. vivax causes milder symptoms in comparison to P. falciparum; they are primarily found in Africa and Asia/South America, respectively. Both P. malariae and P. knowlesi are quite rare and found in Africa and Southeast Asia, respectively [5].

1.2 History of the Outbreak Malaria has consistently brought ruin to countless civilizations, beginning as far back as 2700 BC. During that time, ancient Chinese scriptures documented the first descriptions of malaria-like symptoms, followed by more similar cases after another 1200 years inscribed upon papyrus [6].

Global Health and Malaria: Past and Present

3

Aside from the launch of the Global Malaria Eradication Programme in 1955, the next four decades were considered the greatest failure in the fight against malaria throughout the entire world. Between 1969 and 2000, millions of individuals suffered death, outrageous medical expenses, along with a couple hundred thousand pregnant women dying in childbirth due to malaria-related complications [7]. Millions of children struggled with various symptoms including seizures, disability, and chronic diseases as a result of these birth complications. These statistics crippled economies throughout sub-Saharan Africa, the most directly affected region, leaving people and their countries at a loss for consistent healthcare and resources. The past two decades have proved to be the silver lining for the eradication program with more than 1.5 billion cases, and approximately 7.6 million deaths averted from 2000 to 2019 around the globe.

1.3 Evolution of Treatments The beginnings of antimalarial drugs can be traced back to the 1820s with the chemical isolation of quinine. Unfortunately, this was only the start, as time passed malaria parasites began to show antibiotic resistance rendering numerous drugs ineffective. The discovery of quinine as a viable method of treatment brought forward one of the most effective and longstanding forms of antimalarial treatment. Discovered in the 1820s, resistance to quinine was only first documented in the 1980s [8]. Quinine was followed by the repurposing of mepacrine, initially used as a prophylactic during the Second World War, which was found to have antimalarial properties. Nowadays, mepacrine is not used as a form of viable treatment due to various life-­ threatening side effects such as fatigue, nausea, and diarrhea. Large doses of mepacrine caused yellowing of the skin and in severe cases had induced bone marrow aplasia [9]. Chloroquine (CQ) had been used extensively as the primary defense against malaria since the 1940s. Due to the drugs’ consistent and international use, CQ and hydroxychloroquine (HCQ)-resistant malarial parasites began to make an appearance within 20 years of their application. CQ and HCQ are still used in some regions of the world where P. vivax is the predominant malarial plasmodium due to its continued susceptibility [10]. Amodiaquine synthesized in 1948 functionally similarly to chloroquine and was specifically used in treatment of less complicated cases of P. falciparum. In order to combat the increasing resistance to chloroquine, a large variety of drugs were synthesized by numerous countries and research programs (e.g., amodiaquine, piperaquine, lumefantrine, proguanil, atovaquone, pyrimethamine, sulfadoxine, pyronaridine, mefloquine, halofantrine). However, most of these drugs have seen an increase in antibiotic resistance or produce undesirable and even life-threatening side effects [8]. More recently, Nobel Prize Laureate Youyou Tu’s discovery of artemisinin in 1971 has proven incredibly effective in treating chloroquine-resistant plasmodium. Not only CQ-resistant malaria but artemisinin had been found to be effective against all forms of drug-resistant malaria caused by

4

S. Sankineni et al.

P. falciparum. The first reports of artemisinin resistance were documented in 2008. Following artemisinin, the Walter Reed Army Institute of Research in Maryland synthesized tafenoquine. Tafenoquine is presented as a one-dose antibiotic solution for P. vivax for the first time in 60 years. On the other hand, the Center for Disease Control (full form) recommends that tafenoquine be prescribed alongside chloroquine only for the treatment of P. vivax but can be used as a possible radical cure for P. ovale on its own [11].

2 Malaria Across the World 2.1 Sub-Saharan Africa The sub-Saharan African region suffers from some of the highest rates of malaria morbidity and mortality rates worldwide. An estimated 90% of malaria deaths resulting from P. falciparum are concentrated in this region [12]. Malaria infection is common in the Sahel region of Africa; it is considered endemic specifically in the countries of Nigeria, Democratic Republic of the Congo, Mozambique, Tanzania, Niger, and Burkina Faso (WHO). Although malarial infection is common in the region, death caused by the disease is not nearly as frequent, due to an acquired functional immunity. Unlike certain pathologies like tuberculosis, the presence of the virus does not signify the disease; its presence is considered universal in populations in the region. The majority of the death toll in sub-Saharan Africa is comprised of young children and those with weak immune systems who are most vulnerable to the disease (Fig. 1). Malaria affects children most severely in three different ways. First, infection during pregnancy leads to low birth weight and premature births, which are major risk factors for death. As a result of malaria infection, young children are also vulnerable to acute febrile illness and chronic repeated infections. These infections often lead to severe anemia and cerebral malaria (i.e., seizures, coma) which greatly increase their risk of death. Advances in science make malaria easily preventable and treatable. Poverty and insufficient health care vastly increase the risk an infected child is able to be treated promptly and effectively. Approximately 93% of malaria cases worldwide in 2018 are located in sub-Saharan Africa (WHO). Of these, two-­ thirds of the death toll comprised of children under 5 years old (Fig. 2). South of the Sahara Desert contains regions with tropical and subtropical climates which are optimal for the female parasite development of the Anopheles mosquito [13]. In 2017, an estimated 200  million cases were located in the African region [14]. In response to these staggering statistics, malaria is considered an urgent public health priority, and major programs have been implemented in the global malaria response. From 2000 to 2019, the mortality rates for children under 5 years old decreased from 84% to 67% [15]. The use of insecticide-treated mosquito nets (ITNs) has been regularly proven effective in reducing malaria-related

Global Health and Malaria: Past and Present

5

Fig. 1 [31]: The graph depicts the death rate resulting from malaria in sub-Saharan Africa from the years 2000 to 2017. Other than a gradual incline till 2003, there is a consistent decline in deaths till 2017

Fig. 2 [31]: The graph depicts the malaria incidences in sub-Saharan Africa from 2000 to 2018. There is a downward trend, showing how the incidences of malaria in the region have continued to decrease since 2000

6

S. Sankineni et al.

deaths and transmission. Millions of ITNs have been distributed across the sub-­ Saharan region, and the use per household continues to increase. However, less than 40% of households have enough ITNs for every family member [12]. The sub-­ Saharan region is expected to have among the highest urban population growth worldwide. How urbanization will affect malaria transmission rates is not well known. However, the plasmodium is expected to breed in different habitats including septic tanks and other urban settings where rapid expansion of the disease may occur [16].

2.2 Northeast Asia Since the 2000s Northeast Asia has seen nearly a 43% decrease in the incidence rate of malaria. However, malaria rates in Papua New Guinea make up nearly 80% of the reported cases within this region, including Papua New Guinea, the Solomon Islands, Cambodia, the Philippines, Viet Nam, Vanuatu, the Republic of Korea, China, and Malaysia. China has reported zero cases of malaria since 2017, while Malaysia has reported zero cases of human malaria since 2018, instead reporting 3212 cases of P. knowlesi in an entirely zoonotic presence [17] (Fig. 3). The initial reaction to malaria within these regions was unavoidable due to the lack of distribution channels and proper medical organizations throughout these

Fig. 3 [31]: The incidence rates have dropped drastically in the Solomon Islands in the past two decades from more than 600 cases per 1000 population to approximately 133 in 2018

Global Health and Malaria: Past and Present

7

countries. Thousands of miles of natural forests and tropical climates breed malaria in indigenous populations with no access to proper medical care or medications. Another contributing factor lies within the expansive counterfeit drug market within this region, and the circulation of unregulated medications is a direct factor in producing drug-resistant malaria mutations. Counterfeit antimalarials make up almost 50% of the malaria medications distributed and supplied within northeast Asian countries. These medications contain enough active ingredients to pass lenient regulation standards but not enough to effectively eliminate the malarial parasite resulting in greater resistance [18] (Fig. 4). Deaths resulting from malaria in this region have dropped approximately 50% percent in the last 19 years. The mortality rates went from 1 per 100,000, to 0.4 per 100,000 of the population at risk, a majority of those deaths arising from Cambodia and Papua New Guinea [17]. High levels of deforestation, considerable temporal, and humidity changes due to climate change, and social behaviors are all contributing factors to the overbearing malaria incidence and death rates in these regions. Climate change has resulted in a more tropical climate suitable for malaria in New Guinea; this, coupled with the region’s more frequent human behavior of travel between indigenous communities and large cities, creates a larger population at risk for this disease [18]. In the past, mosquito nets treated with insecticide were the primary deterrent to malaria-infected mosquitoes. For a majority of the late twentieth century, these nets provided a valuable barrier against the transmission and incidence of malaria

Fig. 4 [31]: Cambodia and Papua New Guinea have struggled combatting their malaria epidemic in the past year with an average of 8 deaths per 100,000 of their population. Exponentially better than that of 17 years in the past, but far from eradication

8

S. Sankineni et al.

amount of the western pacific countries, and no long-term studies took place in these regions to determine the true statistical implications; however, long-term studies detailing the use of treated nets in African regions found that such methods resulted in the prevention of approximately 68% of 600 million cases of malaria [19].

2.3 Southeast Asia The Southeast Asia region shows some of the greatest declines worldwide relative to malaria rates but has carried the burden of the disease for centuries, making it the second highest region with malaria cases globally. The nine endemic countries within this region include the following: Bangladesh, Bhutan, Indonesia, Myanmar, India, Nepal, Sri Lanka, and Thailand. In 2018, the World Health Organization (WHO) reported that there has been a decline of 69% of malaria cases since 2010 [20]. The plasmodia that are most prevalent in the region are P. vivax and P. falciparum. The severity of the disease not only varies by each country but also within areas within the country itself due to varying political structures, climates, and ecological diversity [18]. In India, the ratio of P. vivax to P. falciparum infection rates has been constantly changing with P. vivax rates increasing. The country has decreased its number of incidences of malaria by 50% since 2017 [20] (Fig. 5).

Fig. 5 [31]: The graph depicts malaria incidence from 2000 to 2018 in many endemic countries in the Southern Asian region. India remains the country with the highest remaining incidences. Bhutan shows fluctuations but an eventual decline in 2018. The rest of the countries overall followed a downward trend

Global Health and Malaria: Past and Present

9

Approximately 30% of the morbidity and 8% of mortality relative to global malaria are associated with the Southeast Asia region [21]. The high-priority areas include the forest areas largely due to the increased level of migration through those border regions that usually are along forested regions [22]. Similar to sub-Saharan Africa, those most vulnerable to the disease are children and pregnant women; the risks increase substantially if they are subject to poverty or low socioeconomic conditions [23]. Despite being home to one-fourth of the human population, many in the Southeast Asian region are spread out in rural areas with little or difficult access to suitable health care. Due to the implementation of various treatment programs throughout the region, the Maldives and Sri Lanka have been declared to be malaria free. Bhutan, Bangladesh, and Thailand are also showing a substantial decline in the number of reported malaria cases [24]. One of the largest problems with tackling malaria in the Southeast Asia region is the presence and growth of drug resistance. Artemisinin-based combination therapy (ACT) has been used as the first line of treatment, but the emergence of an artemisinin-­resistant malaria strain has thwarted global aid and initiative to reduce the transmission of malaria in the area [25]. The strain was first found on the border of Thailand and Cambodia along the Mekong River region, highlighting the need for monitoring and transmission control along the borders between endemic countries and those with lower rates. Along with drug resistance strains developing, the continued illegal manufacturing of counterfeit drugs endangers the efficacy of the global initiative against malaria. Future health policy changes should target accommodations to drug resistance and transmission monitoring across international borders.

2.4 The Middle East The WHO Middle Eastern region makes up approximately 5% of the world population. These regions include Sudan, Yemen, Djibouti, Somalia, Afghanistan, Pakistan, Saudi Arabia, and Iran. In the past two decades, the incidence rate of malaria in this region has gone from seven million cases to five million cases in 2019. In the past few years, Sudan has been the greatest contributor of malaria incidence in this region, with an average of 2400 cases according to the WHO’s World malaria report of 2020 [26], reason being newer developments of drug-resistant malaria parasites within endemic regions of Sudan (Fig. 6). Factors such as drug-resistant malaria and travel from neighboring countries are the main influencers of malaria within these countries. Afghanistan, a currently endemic country, is struggling with large counts of asymptomatic malaria with almost 50% of their total population being at risk for infection [27]. Travel from Sudan to other countries in the Middle East region has contributed to imported malaria cases including Saudi Arabia and numerous countries outside of this region. Studies conducted in Iran, a country on the path to eradication with zero indigenous transmission since 2018, have found an incredible 572 cases of malaria all of which were believed to be imported from Afghanistan (Fig. 7).

10

S. Sankineni et al.

Fig. 6 [31]: Despite lower rates of incidence in Sudan in 2015, the rise of drug-resistant strains of malaria has resulted in a steady increase pushing them above Yemen within the past few years

Fig. 7 [31]: Although Somalia is considerably behind in incidence rate, they led with the highest morbidity rates as of 2017, an average of 8 deaths per 100,000 population

Global Health and Malaria: Past and Present

11

2.5 The Americas In the Americas, approximately 765,000 cases of malaria were found, and 340 deaths were reported in the year 2018. Nearly half of the world’s population is at risk of being affected by malaria. However, those living in rural areas or low-income countries have an even greater risk. In the Americas, about 138 million people fall within these high-risk parameters. Of the types of human malaria plasmodium discussed, P. falciparum affects the most across populations in the Americas. Specifically, it is the cause of 77% infections in the region. However, P. vivax is the dominant cause of infection throughout South America, particularly in the Amazon rainforest. Great effort has been put into eliminating malaria from the Americas. Between the years 2000 and 2015, cases in the Americas decreased by 62% [28] (Figs. 8 and 9). Although some countries have shown an increase since 2015, others have shown to be on their way to successfully battling the disease. For instance, the most recent feat has been the eradication of malaria from El Salvador as of 2021, making it the first country in Central America to become malaria free. Other than El Salvador, other countries in South America have also eradicated the disease in recent years. Paraguay was considered malaria free in 2018, while Argentina became malaria free in 2019. Some of the countries within the region that hold the most cases include Ecuador, Suriname, Guyana, Colombia, and Brazil. Due to the poor management in some countries like Venezuela, there has been a persistent increase since early 2000 from about 3600 cases to most recently, a devastating 467,000 in 2019 [29] (Figs. 10 and 11).

Fig. 8 [31]: In the early 2000s, Ecuador and Suriname were leading the incidence rates among the WHO’s region of the Americas. Suriname had an almost four times greater incidence rate than Guyana, in third place, while Ecuador was presenting almost double the rates of Suriname

12

S. Sankineni et al.

Fig. 9 [31]: This figure depicts the incidence of malaria in the Americas (2018) for various countries within the region. Venezuela shows a devastating increase in the number of cases between 2000 and 2018. Contrastingly, Suriname and Ecuador both jumped from having the most incidences to significantly less

Fig. 10 [31]: This graph depicts the death rate from malaria in the Americas (2000) for various countries. Guyana and Suriname have the highest death rates within the region

Global Health and Malaria: Past and Present

13

Fig. 11 [31]: This graph depicts the death rate from malaria in the Americas (2017) for various countries. Although Guyana and Suriname are the highest in terms of death rates, they are still significantly less than 2000. Most of the countries within the region have shown a downward trend for death rates from 2000 to 2018

Along with both P. falciparum and P. vivax, P. malariae also is active in the region; however, it only accounts for less than 1% of the incidences. Although there has been quite an advancement in the elimination of malaria in the Americas, there are many challenges specific to the region that must be overcome to implement change more efficiently and at a greater scale. Some challenges include a dearth of international and domestic funding as well as fluctuating environmental change. Antimalarial resistance and insecticide resistance also greatly hinder malaria’s eradication within the region. Political conflict in endemic countries makes it even more difficult to decrease malaria incidence [30]. Moving forward, the track to decreasing the burden of malaria in the Americas must attempt to overcome these challenges.

3 Conclusion Malaria, although both preventable and treatable, has led to some of the highest death rates across the globe. P. falciparum and P. vivax are two of the most prevalent human infection species of malaria. The regions that carry the burden of the disease include sub-Saharan Africa, Northeast Asia, Southern Asia, Middle East, and the Americas. Over the years, the treatment for malaria has changed. Artemisinin and tafenoquine are only two of more than a dozen groundbreaking antimalarial

14

S. Sankineni et al.

medications discovered or synthesized within the past 50 years. Although malaria is an ever-mutating disease, advancements in science, medicine, and international relations will continue to produce newer, more effective antimalarial drugs. The majority of deaths that occur from malaria in the sub-Saharan African region consist of children and the immunocompromised. Although the region makes up the majority of the deaths from the disease, they have shown a significant decline in cases over the past decade. Insecticide-treated mosquito nets (ITNs) have been proven to be effective in preventing infection from the Anopheles mosquitoes. Currently, Northeast Asia has been struggling to maintain their malaria prevention and treatment standards as they face more and more drug-resistant malarial parasites, due to an uncontrollable counterfeit drug market. Increased travel between rural communities and large cities brings its own set of transmission complications putting larger populations at risk. Hopefully, increasing medication regulations prove effective in curbing the rampant use of counterfeit malarial medications, which are paramount contributors to drug-resistant strains of malaria. These regions should even consider returning to the use of older methods of prevention such as the incredibly effective treated mosquito nets which were widely popular in the late twentieth century. Employing these methods should bring about significant change in the incidence of malaria within these regions in the coming years. The Southern Asian region has shown a great decline in incidences and deaths as well, especially the countries Bhutan and Bangladesh, which are considered to be malaria free. The geography of this region makes it vulnerable to spreading the disease effectively. The climate coupled with the development of antimalarial-­ resistant strains in the region make it difficult to fully eradicate malaria. Still, there has been great progress in the region. The Middle East is another region that has seen incredible decreases in malarial incidence and prevalence into the late twenty-first century. The methods these countries have been employing including prevention and treatment have proven to be effective and have resulted in some of the lowest rates in the world. However, it should still be considered that this region is only composed of about 5% of the global population; hence, enforcing regulations and prevention methods becomes much more feasible on such a scale [27]. Many countries in the Americas recently have been cleared of malaria, showing progress within the region. However, other countries like Venezuela have shown an increased incidence rate. Political instability as well as lack of funding impact the country as well as others to combat the disease. In order to effectively tackle malaria in all of these countries, research on transmission dynamics and rates in urbanized and forested areas should be done. Further studies on antimalarial-resistant strains are also needed as we attempt to treat them. The dearth of funding in many of these regions has left holes in preventative care options for those in need. In addition, it would be great to have a global database on disease spread and drug usage. Currently, each country has its own policies and local databases.

Global Health and Malaria: Past and Present

15

Due to the unexpected and disastrous effects which the coronavirus has wrought upon many countries previously struggling with malaria, we have recently seen antimalarial precautions and treatments being placed on hold across the globe. Unfortunately, these setbacks have pushed the WHO and the Global Malaria Eradication Program’s calendars for eradication further into the future than before.

References 1. National Health Service: Health Conditions, Malaria. https://www.nhs.uk/conditions/malaria/ causes/. 2. World Health Organization: Malaria. https://www.who.int/news-­room/fact-­sheets/detail/ malaria. 3. Stanford Health Care: Types of Malaria Parasites. https://stanfordhealthcare.org/medical-­ conditions/primary-­care/malaria/types.html. 4. Vidhya P, Sunish I, Maile A, Zahid A. Anopheles sundaicus mosquitoes as vector for plasmodium knowlesi, Andaman and Nicobar Islands, India. Emerg Infect Dis. 2019;25(4):817–20. 5. Cox-Singh J, Davis TM, Lee KS, Shamsul SS, Matusop A, Ratnam S, Rahman HA, Conway DJ, Singh B. Plasmodium knowlesi malaria in humans is widely distributed and potentially life threatening. Clin Infect Dis. 2008;46(2):165–71. 6. Rosenthal PJ, John CC, Rabinovich NR. Malaria: how are we doing and how can we do better? Am J Trop Med Hyg. 2019;100(2):239–41. 7. Global Malaria Programme. World malaria report, 2020. Geneva: World Health Organization; 2020. p. 2. 8. Tse EG, Korsik M, Todd MH. The past, present and future of anti-malarial medicines. Malar J. 2019;18(1):93. 9. LiverTox. Clinical and research information on drug-induced liver injury [Internet]. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases; 2012; Mepacrine 10. Lei ZN, Wu ZX, Dong S, Yang DH, Zhang L, Ke Z, Zou C, Chen ZS. Chloroquine and hydroxychloroquine in the treatment of malaria and repurposing in treating COVID-19. Pharmacol Ther. 2020;216:107672. 11. Center for disease Control and Prevention: Change in Krintafel (tafenoquine) Label. https:// www.cdc.gov/malaria/new_info/2020/tafenoquine_2020.html. 12. Against Malaria Foundation: About Malaria. https://www.againstmalaria.com/Faq_ malaria.aspx. 13. Doumbe-Belisse P, Kopya E, Ngadjeu CS, et al. Urban malaria in sub-Saharan Africa: dynamic of the vectorial system and the entomological inoculation rate. Malar J. 2021;20:364. 14. World Health Organization: Malaria. https://www.afro.who.int/health-­topics/malaria. 15. Unicef: Malaria. https://data.unicef.org/topic/child-­health/malaria/. 16. Snow RW, Omumbo JA. Malaria. In: Jamison DT, Feachem RG, Makgoba MW, et al., editors. Disease and mortality in Sub-Saharan Africa. 2nd ed. Washington, DC: The International Bank for Reconstruction and Development/The World Bank; 2006. p. 14. 17. Global Malaria Programme. World malaria report, 2020. Geneva: World Health Organization; 2020. p. 28. 18. Bharati K, Ganguly NK. Tackling the malaria problem in the South-East Asia Region: need for a change in policy? Indian J Med Res. 2013;137(1):36–47. 19. Self L. Controlling Malaria in Western Pacific with mosquito nets treated with Pyrethroids in village communities, 1979-1999. Am J Trop Med Hyg. 2016;95(1):10–4.

16

S. Sankineni et al.

20. World Health Organization: Malaria on the decline in WHO South-East Asia Region; Efforts must continue as risks persist: WHO. https://www.who.int/southeastasia/news/ detail/04-­1 2-­2 019-­m alaria-­o n-­t he-­d ecline-­i n-­w ho-­s outh-­e ast-­a sia-­r egion-­e fforts-­m ust-­ continue-­as-­risks-­persist-­who. 21. MESA Alliance: Malaria vectorial system and new vector control tools in Southeast Asia (Southeast Asia ICEMR). http://mesamalaria.org/mesa-­track/ malaria-­vectorial-­system-­and-­new-­vector-­control-­tools-­southeast-­asia-­southeast-­asia. 22. Seidlein L, Peto T, Tripura R, et al. Novel approaches to control malaria in forested areas of Southeast Asia. Trends Parasitol. 2019;35(6):388–98. 23. Kondrashin AV.  Malaria in the WHO Southeast Asia region. Indian J Malariol. 1992;29(3):129–60. 24. Global Malaria Programme. World malaria report 2010. Geneva: World Health Organization; 2010. p. 25. 25. Kumar A, Chery L, Biswas C, et al. Malaria in South Asia: prevalence and control. Acta Trop. 2012;121(3):246–55. 26. Global Malaria Programme. World malaria report, 2020. Geneva: World Health Organization; 2020. p. 26. 27. Al-Awadhi M, Ahmad S, Iqbal J. Current status and the epidemiology of malaria in the Middle East region and beyond. Microorganisms. 2021;9(2):338. 28. Pan American Health Organization: Malaria. https://www.paho.org/en/topics/malaria. 29. Global Malaria Programme. World malaria report 2010. Geneva: World Health Organization; 2010. p. 30. 30. Conn J, Grillet M, Correa M, Sallum M.  Malaria transmission in South America—present status and prospects for elimination. In: Towards malaria elimination  – a leap forward. IntechOpen; 2018. p. 12. 31. Roser M, Ritchie H. “Malaria”. 2019; Published online at OurWorldInData.org. Retrieved from: https://ourworldindata.org/malaria

Malaria: Cellular Understanding of Disease Arnold Donkor Forkuo and Kofi Oduro Yeboah

Abstract Malaria infection triggers immune responses, critical for limiting Plasmodium parasite infections and severity of disease manifestation. Albeit repetitive exposures to the parasite lead to the development of nonsterile natural immunity to asexual forms of Plasmodium, only partial protection of the host against disease manifestation results. Thus, naturally acquired immunity against malaria occurs inefficiently, and protection is relatively short-lived. Moreover, the intensity of the immune response to Plasmodium parasite is stage-specific. However, the stages comprise of a wide array of effector mechanisms that can be exploited to achieve efficient immunity against malaria infection. Understanding the humoral and cellular adaptive immune responses against liver stages of malaria infection is crucial in the development of vaccines that can generate desired vaccine-induced responses. Optimal vaccine-induced responses will aid in the achievement of sterilizing immunity. Likewise, it is imperative to fully elucidate immune effector mechanisms involved in the development of immunity against erythrocytic forms of Plasmodium. Mimicking this natural immunity to blood stages has been the strategy with some malaria vaccines being investigated for effectiveness in the reduction of malaria-related morbidity and mortality. This chapter focuses on protective immune responses to malaria infection and also highlights the areas of immense relevance to the development of malaria vaccines. Here, we review recent advances and explore emerging hypotheses regarding the molecular and cellular pathways that regulate Plasmodium parasite-specific humoral immunity. Keywords  Malaria · Plasmodium · Erythrocytic stage · Preerythrocytic stage · Cerebral malaria · Humoral · Malaria vaccine

A. D. Forkuo (*) · K. O. Yeboah Department of Pharmacology, Faculty of Pharmacy and Pharmaceutical Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 R. Shegokar, Y. Pathak (eds.), Malarial Drug Delivery Systems, https://doi.org/10.1007/978-3-031-15848-3_2

17

18

A. D. Forkuo and K. O. Yeboah

1 Malaria and the Immune System Like most other infectious diseases, malaria infection triggers innate and adaptive immune responses [1]. This has been understood since Koch’s hypothesis in the early twentieth century, which posited that individuals living in malaria-endemic regions may develop nonsterilizing immunity against natural Plasmodium infections. Koch postulated that this immunity may protect children against clinically significant diseases following repeated exposures over several years [2]. Although current evidence supports the development of nonsterile natural immunity to asexual forms of Plasmodium upon repetitive exposures to the parasite, recent findings show that this only provides partial protection of the host against disease manifestation [3, 4]. Because this immunity dwindles quickly in the absence of reinfection, sterilizing immunity is not achieved, enabling Plasmodium to mature and survive even in low-transmission seasons [4, 5]. This makes eradication an arduous task. Nonetheless, partial immunity enables individuals in endemic areas to control parasitemia and develop subclinical disease [5]. Albeit the exact mechanism underlying clinical immunity against Plasmodium is not fully described, evidence suggests the key involvement of cytophilic antibodies and memory cells which are produced during repeated exposures to Plasmodium [5]. Moreover, following Plasmodium infection, the innate immune system is triggered as the first line of defense, followed by activation of adaptive immune response [5]. In spite of the protection offered by immune activation against various stages of the infection, the parasite through multiple mechanisms can survive the host’s immune response, like the expression of knobs on the surface of infected red blood cells, and establish clinically as a significant disease [2]. This chapter mainly focuses on the general features of what constitutes a protective immune response to malaria infection and also highlights the areas of immense relevance to the development of malaria vaccines.

2 Innate Immunity and Inflammatory Response The pathology of malaria and its clinically associated spectrum of events are largely due to red blood cell-borne asexually reproducing forms of the Plasmodium parasites [4]. Different stages of these asexually reproducing forms within the host can trigger a variety of complex immune responses. The intensity of the immune response is stage-specific, with the erythrocytic stage having a higher response compared to preerythrocytic stage [6], thus explaining why the preerythrocytic stage, comprising of sporozoites and exoerythrocytic forms, is associated with little pathology and no clinical features [7]. Nonetheless, this does not support the view that the preerythrocytic stage is immunologically quiescent and that Plasmodium parasite can completely evade immune detection while replicating within the host hepatocyte. Instead,

Malaria: Cellular Understanding of Disease

19

inflammatory cell activation has been identified to be present within the liver during the exoerythrocytic development of Plasmodium parasite [8, 9]. In addition, quantitative studies with Plasmodium berghei and Plasmodium yoelii showed that a proportion of the parasites that lose motility following inoculation into the skin by the vector can develop into skin exoerythrocytic forms, capable of initiating immune responses [10]. Moreover, the major immune components identified to be present during preerythrocytic and erythrocytic stages are CD8+ T lymphocytes and antibodies, respectively [6].

2.1 Innate Response to Preerythrocytic Forms At the preerythrocytic stage, the immune response is targeted against free sporozoites and infected hepatocytes. Thus, the production of antibodies against free sporozoites and circumsporozoite protein (CSP), to neutralize specific proteins required for cell traversal and invasion, is a crucial immune response aimed at inhibiting Plasmodium invasion of hepatocytes [6]. In addition, some of the antibodies produced by immune cells also activate complement fixation, phagocytosis, and cell lysis. Moreover, these antibodies recognize parasite neoantigens located at the surface of infected hepatocytes and initiate cell kill via antibody-dependent cellular cytotoxicity mechanism [11]. In a study to identify the relationship between RTS, S vaccine-induced antibodies, and protection against Plasmodium falciparum (P. falciparum) infection, it was identified that antibodies against CSP and CD4+ T-cell responses serve as good correlates of protection [12]. As shown in Fig.  1, CD8+ effector T cells through the production of interferon-γ (IFNγ) also provide robust protection against the Plasmodium parasite, by killing intrahepatic parasites during the preerythrocytic stage [6, 13]. To clarify, CD11c+ cells acquire Plasmodium antigens, traffic to the liver draining lymph nodes, and then present peptides to naïve CD8+ T cells [14]. Prior to the activation and expansion of CD8+ cells and other antigen-specific T cells during the early phases of the infection, natural killer cells through cooperation with myeloid cells produce inflammatory cytokines such as IFNγ. Interestingly, IFN-γ has been shown to be an important effector molecule critical to both innate and adaptive immunity. Indirectly, this cytokine leads to destruction of parasite-­ infected hepatocytes (Fig. 1) [15, 16]. Moreover, natural killer and natural kill T cells produce type I interferons, as well, which enhances the elimination of intrahepatic parasites. Interestingly, P. falciparum, unlike viruses and bacteria, can trigger the production of type I IFNs in the absence of Toll-like receptors (TLRs) 3 and 4, and their signaling proteins myeloid differentiation factor 88 (MyD88) and Toll/interleukin-1 receptor domain-containing adaptor protein inducing interferon beta (TRIF) [6]. In contrast, P. falciparum uses melanoma differentiation-associated gene 5 protein (MDA5) and in addition to other signaling proteins such as the mitochondrial antiviral signaling protein (MAVS) [18].

20

A. D. Forkuo and K. O. Yeboah

Fig. 1  Liver stage infection. Following invasion of hepatocytes, macrophages produce IL-12 which stimulates NK cells to produce IFN-γ. In part, this serves to augment the immune response directed against infected hepatocytes [17]. Although unproven, it is plausible that NK cells may also kill infected hepatocytes or sporozoites. CD 8 Cluster of differentiation 8, IHs infected hepatocytes, Mø macrophages, NK natural killer cells

Given the above, the preerythrocytic stage may be associated with little pathology and probably of less clinical relevance. However, the stage comprises a wide array of effector mechanisms that can be exploited in the development of effective vaccines against malaria infection.

2.2 Innate Immune Response to Erythrocytic Forms In contrast to the preerythrocytic stage of Plasmodium invasion, high levels of inflammation that lead to clinical symptoms have long been recognized in the erythrocytic stage [8, 19]. The inflammatory involvement is due to the release of certain molecules from infected erythrocytes that accompanies the egress of the parasite out of infected erythrocytes. These immunogenic molecules include merozoites and erythrocyte cellular contents. Studies into these molecules have led to the establishment of several pro-inflammatory molecules that either take their origin from the Plasmodium parasite or are derived indirectly from the infection of erythrocytes [8]. Among the molecules derived directly from the parasite, glycosylphosphatidylinositol (GPI) anchors were discovered to mediate signal transduction in the host cell and promote inflammatory responses [20]. These glycolipid anchors function as cell-surface proteins that anchor parasite proteins to the plasma membrane in the merozoite and activate preferentially TLR-2/TLR-6 and TLR-2/TLR-1 heterodimers and TLR-4 homodimers [21, 22]. In spite of the stimulation of immune

Malaria: Cellular Understanding of Disease

21

response in  vivo, the role of glycosylphosphatidylinositol in malaria-induced inflammation in patients remains unclear. Other parasite-derived pro-inflammatory molecules include hemozoin and parasite RNA. On the other hand, host components that may contribute to inflammation during parasite egress out of erythrocytes include uric acid accumulation and oxidative stress, among other components. To clarify, Plasmodium parasite uses hypoxanthine as a uric acid precursor for the synthesis of nucleic acids needed during parasite replication. However, at the end of the replication cycle, parasite requirement for hypoxanthine decreases resulting in the accumulation of hypoxanthine within the infected erythrocyte [23]. Following egress of parasite out of infected erythrocytes, precipitates of uric acid and also soluble hypoxanthine obtained from the parasite’s parasitophorous vacuole are released [24]. These can trigger an inflammatory response through activation of the NOD-like receptor protein 3 (NLRP3) inflammasome [25]. Interestingly, uric acid is reported to mediate mast cell activation in a mouse model of malaria, resulting in regulation of a subset of dendritic cells, and subsequent activation of CD8+ T-cell responses directed against the parasite [26]. Likewise, clinical response in malaria patients following treatment with a xanthine oxidase inhibitor showed more rapid reduction of the inflammatory response [8, 27].

2.3 Cellular Defenses in Malaria 2.3.1 Hepatocytes Following the inoculation of sporozoites in the host skin by the female Anopheles mosquito, majority of sporozoites enter bloodstream and subsequently reach and invade the liver. The process of invasion is facilitated by CSP, the major antigen located on the sporozoite surface, and the micronemal protein, thrombospondin-­ related anonymous protein [28]. After invasion, sporozoites then form parasitophorous vacuoles where they undergo remarkable differentiation into thousands of highly metabolically active merozoites [29]. During this process of differentiation, genomic components of the parasite, specifically its double-stranded RNA, gain access to the cytosol of the hepatocyte and trigger the release of type I IFNs via activation of MDA5/MAVS/IRF3/7 cytosolic signaling pathway [9]. Through the production of interferon-stimulated genes and subsequent INFα activation in nearby hepatocytes, the initial signal is propagated in an autocrine and paracrine manner. This is believed to aid in the activation of accessory immune cells such as natural killer T cells, enabling the host to control parasite burden in the liver [30, 31]. Moreover, INFα/natural killer T-cell-mediated control of hepatic parasite burden is dependent on IFNγ, which has been shown to directly kill intrahepatic parasites [9] (Fig. 2).

22

A. D. Forkuo and K. O. Yeboah

Fig. 2  Innate immune responses during the liver stage of Plasmodium infection. Invasion of hepatocytes by Plasmodium parasites activates interferon regulatory factors (IRF), which induce transcription of type I interferons (IFN), namely, IFNα and IFNβ. Subsequently, secreted IFNα and IFNβ activate IFNα/β receptor (IFNAR) in an autocrine or paracrine manner. IFNAR signaling results in transcription of IFN-stimulated genes (ISGs), which includes chemokines, such as CXCL9 and CXCL10. It is believed that upon secretion from hepatocytes, these chemokines recruit cells expressing the corresponding chemokine receptor CXCR3. These cells include natural killer (NK), T, and NKT cells which upon activation by type I IFN contribute to limiting Plasmodium liver stage expansion through the secretion of IFNγ [32].

2.3.2 Granulocytes Evidence from in vivo studies of malaria using rodent models suggests that mast cells may contribute to the clearance of malaria parasites [33]. Through the production of fms-like tyrosine kinase 3 (Flt3) ligand and the subsequent induction of proliferation of a dendritic cell subpopulation, mast cells promote innate immune activation during malaria infection in mice. This finding is significant since both Flt3 ligand and the dendritic subpopulation have been found to be elevated in patients with malaria [26]. Thus, mast cells are relevant and may account in part, for the clearance of Plasmodium by the host. In addition to mast cells, circulating neutrophils are significantly increased during malaria infection [9]. The level correlates with inflammatory responses and severity of the disease [34, 35]. Evidence from murine studies shows that adoptive transfer of these granulocytes from infected rats provides partial protection against infection, thus indicating the role neutrophils play in protection against malaria [36]. Nevertheless, neutrophil levels have also been implicated in progression of malaria infection caused by certain Plasmodium species. For instance, during infection with Plasmodium berghei, neutrophils secrete the chemokine CXCL10 which inhibits the control of parasitemia during the erythrocytic stage. However, reduction in neutrophil levels did not prevent the progression of the disease and the development of cerebral malaria [37].

Malaria: Cellular Understanding of Disease

23

2.3.3 Other Immune Cells Immune cells such as macrophages, dendritic cells, and γδ T cells have also been shown to contribute to clearance of the parasite in various studies. For instance, macrophages contribute to clearing of the parasite through efficient phagocytosis of infected erythrocytes [38]. Within the macrophage, the phagocytosed erythrocyte undergoes degradation in acidic phagosomes [39]. Phagocytosis of infected erythrocytes may proceed in a non-opsonic or opsonic manner, with the former mediated by binding of infected erythrocytes to the scavenger receptor cluster of differentiation 36 (CD36). Opsonic phagocytosis of merozoites, on the other hand, is mediated by complement receptor-1 and Fc-γ receptors and is believed to be a relevant mechanism that contributes to protective immunity in humans [40, 41]. Protective immunity to malaria infection is also enhanced by dendritic cells which are important for the initiation of both innate and adaptive immune responses to Plasmodium parasites. Different pathogen signals can lead to the activation of dendritic cells, unlocking their function as antigen-presenting cells that can efficiently activate naïve T cells [42]. A subtype of T-cell population that expands in peripheral circulation during malaria infection, especially infection with P. falciparum, is γδ T cells. Without being limited by MHC antigen presentation, this minority of T-cell population recognizes self- and non-self-antigens and is activated by phosphoantigens produced by apicoplast of the parasite [43]. Following activation, γδ T cells release cytotoxic granules that contain granulysin, a cytolytic and pro-inflammatory molecule that kills merozoites [44]. In addition, γδ T cells have been shown in murine studies to enhance parasite clearance through the production of IFNγ and subsequent activation of dendritic cells [45, 46].

2.4 Cytokine Response The inflammatory response during an acute malaria infection is characterized by high circulating levels of a variety of cytokines including IFN-α, IFN-γ, IL1β, IL-6, and TNF. The plasma levels of these cytokines directly correlate with severity of the disease, especially in Plasmodium vivax (P. vivax) and P. falciparum infections [47]. Likewise, gene expression analysis of peripheral blood mononuclear cells and brain tissues from patients with cerebral malaria confirms elevated levels of inflammatory cytokines [48]. Evidence from rodent studies has shown that the pro-inflammatory cytokine TNF is produced early in Plasmodium infection and is relevant for the clearance of both hepatic and erythrocytic stages of the parasite [9]. This protection against Plasmodium parasite is provided through the production of nitric oxide [49]. In human studies, the levels of TNF have been shown to correlate with disease severity. Strikingly, these levels are highly elevated in fatal cases of cerebral malaria [50]. Furthermore, studies in children from endemic areas of the disease have shown that

24

A. D. Forkuo and K. O. Yeboah

different alleles of the promoter region of TNF are associated with either decreased or increased susceptibility to cerebral malaria and severe anemia [51]. Findings from these studies indicate that TNF expression may be necessary for reduction in parasitemia. However, results from a clinical trial that investigated the use of anti-­ TNF antibodies as adjunctive treatment for cerebral malaria patients showed no survival benefits in these patients [52], thus highlighting the complexity of cytokine response in malaria infection. In spite of the complex role of cytokines in the development and progression of the disease, IL-12 and IL-18 have been established in murine models of malaria to contribute to parasite clearance. The protection offered by these cytokines against malaria infection is probably mediated by the pragmatic effect on IFN-γ production [9]. Nonetheless, high levels of IFN-γ can be vicious, since the production of IL-12-­ dependent IFN-γ in response to malaria parasites may induce liver injury [53]. Moreover, the levels of protective cytokines such as IL-10 are also highly expressed during malaria and have been shown to correlate with disease severity. It is believed that these anti-inflammatory cytokines are elevated as a response to increased levels of pro-inflammatory cytokines during acute infection [54]. For this reason, it is considered more informative and relevant to measure the ratio between pro-­ inflammatory and anti-inflammatory cytokines, such as IL-6/IL-10 or IFN-γ/IL-10, rather than the independent levels of each specific cytokine [9].

3 Adaptive Immunity to Malaria The development of naturally acquired immunity to malaria is a strong incentive that drives efforts targeted at the development of malaria vaccines. With both humoral and cell components, these efforts are multifarious, targeted at triggering adaptive immunity against hepatic-stage infections. As previously mentioned, natural immunity develops to asexual forms of Plasmodium upon repetitive exposures to the parasite, although this protection may be short-lived [3, 4].

3.1 Adaptive Immunity in Preerythrocytic Infection Malaria parasites possess membrane proteins that are crucial for host-cell invasion and also sequestration within blood vessels and in bone marrow niches. Parasite expression of some of these antigens is stage-specific and serves as targets for host-­ derived antibody interactions during natural infection [4]. This antigen-antibody interaction contributes to the development of acquired immunity to infections caused by asexual forms of the parasite, aiding in the provision of sterilizing immunity to malaria infections. Nonetheless, antigens expressed on erythrocytic sexual forms can also elicit antibody responses during natural infection, with increments in antibody levels following repeated transmission cycles. As a result, some of these

Malaria: Cellular Understanding of Disease

25

antigens are being explored as potential targets for transmission-blocking malaria vaccines [55]. 3.1.1 Antibody Response to the Preerythrocytic-Stage Parasite Antigens present on sporozoite membrane surfaces trigger antibody interactions at specific stages. Through various distinct mechanisms, this stage-specific antibody response inhibits sporozoite infection. With the help of modern tools such as intravital microscopy and fluorescent sporozoites, antibody interaction with malaria parasite is better understood. These techniques have provided wonderful opportunities for the study of the role of antibodies in the inhibition of preerythrocytic infections. First, following inoculation of sporozoites into the skin by an infected vector, sporozoite-specific antibodies produced during a previous infection reduce the deposition of sporozoite into the dermis. These sporozoite-specific antibodies also suppress sporozoite motility and thus inhibit their trafficking into blood vessels (Fig.  3). This is supported by findings that mice previously immunized with radiation-­attenuated sporozoites upon exposure to bites from infected vectors demonstrated reduced sporozoite numbers in the dermis compared to the control group [56, 57]. This incomplete obstruction to sporozoite release from infected vectors is believed to be a result of immune complex formation between the parasite’s soluble circumsporozoite protein and anti-circumsporozoite protein antibodies produced by immunized mice [57]. Similarly, passively immunizing mice with anti-circumsporozoite protein antibodies reduced the deposition of sporozoites into dermis following exposure to bites from infected vectors. Strikingly, results from blood smears demonstrated that none of the immunized mice developed parasitemia [57, 58]. Thus, anti-sporozoite antibodies can also reduce the motility of sporozoites and inhibit target cell invasion. This effect is crucial since it prevents the trafficking of sporozoites to the liver and, as such, inhibits infection of hepatocytes. In the event that sporozoites traffic into bloodstream, anti-circumsporozoite protein antibodies may increase sporozoite opsonization and phagocytosis. Thus, reduce the number of sporozoites that can cause hepatocyte invasion (Fig. 3c). This is the mechanism by which some malaria vaccines offer protective immunity in humans [59]. To clarify, sporozoites coated with anti-circumsporozoite protein antibodies show limited motility resulting in the suppression of sporozoites’ ability to disrupt and migrate through plasma membranes of liver cells (Fig. 3c). As previously mentioned, the capability of these sporozoite-specific antibodies to limit hepatic-stage infection is thought to be responsible for the partial efficacy of the world’s first malaria vaccine, RTS,S/AS01. This is a recombinant protein-based vaccine consisting of circumsporozoite fused to hepatitis B surface antigen [60]. Given the above, humoral immune response during hepatic-stage infection reduces parasite burden in the liver. Thus, the antibodies significantly contribute to the effectiveness of contemporaneous cell-mediated immune response, such as CD8

26

A. D. Forkuo and K. O. Yeboah

Fig. 3  Adaptive immune responses to preerythrocytic stage of malaria parasite. (1) Following whole sporozoite vaccination (WSV) or infection, sporozoite-specific CD8 T cells are primed within the skin-draining lymph nodes (dLNs). It is unclear if the skin dLN is also a site for B-cell priming or a location for CD4 T cells to provide help to CD8 T cells and B cells. After WSV or infection, antibodies and antigen-specific T cells are released into the blood where they can traffic throughout the body to provide multiple levels of protection, as described in (2)–(5). (2) After bites from an infected mosquito, sporozoite-specific antibodies can reduce deposition of sporozoites into the dermis. Sporozoite-specific antibodies also inhibit sporozoite motility and reduce their entry to the underlying blood vessels. (3) Sporozoites travel through the blood to the liver where sporozoite-specific antibodies can enhance opsonization by macrophages and reduce sporozoite motility. This results in inhibition of hepatocyte invasion and subsequent cell traversal. (4) Using differential effector mechanisms depending on the rodent Plasmodium species, CD8 T-cell mediates the killing of infected hepatocytes (5). A role for cytotoxic CD4 T cells has been described in multiple models, but the mechanism as to how these cells contribute to sterilizing protection needs further investigation. It is believed that infected hepatocytes upregulate class II MHC and become direct targets of cytotoxic CD4 T cells. Alternatively, CD4 T cells may inhibit infection via IFNγ production [56].

T-cell response, by reducing the population of infected hepatocytes that need to be targeted. 3.1.2 Cell-Mediated Immune Response to the Preerythrocytic Parasite In addition to providing innate immune response to intrahepatic Plasmodium parasites, parasite-specific CD8 T cells can target antigens expressed on specific liver stages of the parasite and provide sterilizing immunity [61]. The protection offered by this subpopulation of MHC class I-restricted T cells against Plasmodium has been established by various studies using radiation-attenuated sporozoites-­ immunized rodents [56].

Malaria: Cellular Understanding of Disease

27

Evidence from several studies shows that Plasmodium-specific CD8 T cells protect against malaria infection by targeting and killing liver-stage-infected hepatocytes [56, 62]. The direct killing of infected hepatocytes occurs via a mechanism that requires multiple antigen-specific CD8 T cells [63]. In addition, CD8 T cells are associated with killing of a single infected hepatocyte. Thus, this explains why large numbers of CD8 T cells are required for protection against malaria [64]. This role of CD8 T cells in the provision of sterilizing immunity may be augmented by the less studied CD4 T cells. CD4 T cells, also known as T helper cells, can differentiate into various subsets such as Th1, Th2, Tfh, Treg, and ThCTLs, in response to diverse stimuli [65]. Although fairly studied in other settings, T helper cell differentiation in response to malaria infections has not been fully elucidated, partly due to lack of identifiable epitopes that can induce detectable responses. However, it is believed that differentiation to Tfh may play a crucial role in antibody response to liver-stage antigens [56]. Most likely, Tfhs may enhance the formation of B cells and the production of antibodies against sporozoites and thus enhance the achievement of sterilizing immunity following vaccination. However, this interaction between T helper cells and B cells needs further investigation to identify specific components of the interaction responsible for the protective response. In spite of the lack of required studies on the role of T helper cells in malaria, few studies have discovered a crucial role of T helper cells in the proper functioning of CD8 T cells in malaria infections. To clarify, T helper cells through the production of IL-4 enhance the expansion and survival of effector and memory CD8+ T cells after sporozoite infection, thus determining the size of the CD8 T-cell memory pool after whole sporozoite vaccination or immunization with radiation-attenuated sporozoites [66]. It is worth noting that memory CD8 T cells that formed in the absence of T helper cells exhibited normal effector functions and were ineffective in protecting against sporozoite challenge. This implies that, in the absence of T helper cells, significantly fewer antigen-specific CD8 T cells are produced, resulting in an impuissant protection against hepatic-stage infection. To summarize, humoral and cellular adaptive immune responses against the liver stage of malaria infection are crucial for the development of protection against malarial. The steps involved in this process must well be studied in order to rightfully manipulate to generate desired vaccine-induced responses. These immune responses will aid in the achievement of sterilizing immunity.

3.2 Adaptive Immune Response to Erythrocytic Stage Infection Although adaptive immune responses develop against Plasmodium parasite during preerythrocytic stages of malaria infection, progression of the disease is often not aborted. Following the rupture of liver schizonts, several merozoites are released into the blood where they invade erythrocytes. Within the erythrocyte, schizonts divide mitotically, forming erythrocytic schizonts that may contain up to 20

28

A. D. Forkuo and K. O. Yeboah

daughter merozoites each. Subsequently, a cyclical erythrocytic-stage infection develops following reinfection of fresh erythrocytes by merozoites [67]. In addition, a subset of developing merozoites differentiates into gametocytes by an unknown mechanism and can be taken up by an anopheles mosquito during the process of feeding on an infected host [67]. Interestingly, erythrocytic forms of the parasite can trigger adaptive immune responses, aimed at reducing parasitemia. The adaptive immune responses triggered against various blood stages of the parasite provide three kinds of immunity, which unfold at different rates. These immune responses, however, do not provide complete protection against reinfection but rather reduce peak parasitemia, severity, and lethality associated with the infection. This immunity develops over time, with frequent exposure to the parasite [69]. For instance, individuals who emigrate out of malaria endemic areas lose immunity against high parasitemia and severe infection in the absence of exposure [69]. Nevertheless, mimicking natural immunity to blood stages as a strategy with some malaria vaccines may reduce malaria-related morbidity and mortality. As such, it is imperative to fully elucidate immune effector mechanisms involved in the development of this immunity. 3.2.1 Mechanism of B-Cell and Antibody-Mediated Protection The role of antibodies in the clearance of malaria parasites or reduction of parasitemia is critical, as shown in seminal passive transfer studies [70]. In one study, the transfer of IgG from immune adults to pediatric patients with clinical disease resulted in a 3–4 log reduction of parasitemia. Similarly, naturally infected Thai adults who received West African sera–containing antibodies demonstrated a reduction in parasitemia. This shows that sera from one region can still be effective in eliminating malaria parasites in another region, though the parasites may be genetically different [68]. Moreover, both murine and human studies have shown the relevance of B cells in the protection against malaria, specifically in the complete clearance of the Plasmodium parasite [71]. Interestingly, antigen-specific B cells produced during malaria can be detected in both mouse and human subjects using an enzyme-linked immunosorbent spot assay. The detection of these antigen-­ specific B cells can still be done long after a single infection, indicating the capability of malaria infection to induce memory B-cell production [72, 73]. Although the targets of protective antibodies produced during malaria infection are still not clearly identified, two classes of antigens have generally been considered as likely targets. One such class of target antigens is variant surface antigens, exported to the surface of red blood cells following parasite invasion [74]. The other class of target antigens is proteins expressed on merozoite surfaces, used during processes of parasite attachment and invasion of red blood cells [75, 76]]. In P. falciparum malaria, four kinds of variant surface antigens have been described. These include P. falciparum erythrocyte membrane protein 1 (PfEMP1), repetitive interspersed family proteins (RIFIN), sub-telomeric variable open reading frame proteins (STEVOR), and surface-associated interspersed gene family proteins (SURFIN).

Malaria: Cellular Understanding of Disease

29

Although the association between antibodies’ interaction with variant surface antigens and the resultant protection they provide is robust, identifying specific molecules involved in this process has proven challenging. However, the majority of antibodies that interact with variant surface antigens appear to recognize, specifically, variants of PfEMP1 [77]. These variants are encoded by three groups of var genes, namely, groups A, B, and C, which are expressed depending on the severity of the disease. The latter is associated with asymptomatic infections, whereas groups A and B are associated with severe and symptomatic infection [78]. Most importantly, antibodies targeting these variants of PfEMP1 offer protection against severe disease [68]. In addition to variant surface antigen-specific antibodies, antibodies that target merozoite surface proteins also offer protection against malaria. Studies have shown that antibodies that target merozoite surface protein (MSP)-3, apical membrane antigen 1 (AMA1), and some other proteins are normally associated with protection [76]. For this reason, the majority of these surface proteins have been proposed as vaccine candidates. Findings from a study that investigated the relevance of antibodies that target MSP-119 in naturally acquired immunity showed that sera from individuals containing MSP-119-specific antibodies are effective in inhibiting P. falciparum growth. Thus, the MSP-119 antigen may be very beneficial for vaccine development. 3.2.2 Mechanism of T-Cell-Mediated Protection Innate and adaptive immunity are inseparably linked as the cytokines generated by innate immune cells modify the outcome of the adaptive response (Fig. 3). Similar to its role in preerythrocytic infection, the T helper cell through its ability to enhance B-cell formation and phagocytosis of malaria parasites can control malaria infection [79]. As shown in previous studies, T helper cells through the production of IFN-γ can control peak of parasitemia during the acute phase of erythrocytic-stage infection [68]. For instance, immunocompromised animals with deleted IFN-γ have been shown to be unable to control parasitemia [80]. Moreover, in a landmark study by Pombo et  al. [81], repeated inoculations of blood-stage parasites were associated with stronger induction of T helper cell-­ mediated responses. These immune responses, including increased IFN-γ production, protected the subjects from developing an infection following a similar challenge. In addition to IFN-γ, T helper cells also produce TNF and IL-21 which also correlate with parasitemia and are required for complete clearance of Plasmodium parasite [82]. In high transmission areas, T helper cells produce IFN-γ and TNF as predominant cytokines in response to P. falciparum infection in adults, whereas IL-10 is the predominant cytokine produced by T helper cells in children. On the other hand, IFN-γ and TNF are the predominant cytokines produced by T helper cells in both children and adults in low transmission areas [83]. Furthermore, the production of T helper cells that co-produce IFN-γ/IL-10 and also express T-bet, a T helper 1 (Th1) transcription factor, inversely correlates with the duration of infection [84].

30

A. D. Forkuo and K. O. Yeboah

Evidence from experimental animal studies has also implicated CD8+ T cells in the development of immunity against erythrocytic stage of malaria. However, it is believed that the induction of CD8+ T cells leads complete parasite clearance and removal of erythrocytes in the spleen, which results in severe anemia [85]. In this regard, the overall benefit of CD8+ T-cell induction as a vaccine strategy needs further investigation.

3.3 Why Does Immunity Wane in the Absence of Exposure? Given the above discussion, one fundamental question develops, “Why does better, long-lasting immunity to malaria not develop?”. It has been proposed that functional defects in dendritic cells during the erythrocytic stage and the polymorphic nature of most of the disease’s antigens are partly responsible for the lack of better adaptive immunity to malaria [68]. Recently, it has been proposed that dysregulation of the activities of B and T cells of the adaptive immune system is responsible for incomplete immunity [86]. The dysregulated B- and T-cell responses lead to de-escalation of immune response against Plasmodium parasite, thus enabling the parasite to augment its ability to transmit by surviving as a chronic infection. For this reason, the host is able to minimize pathological damage caused by an unrestrained immune response [68]. Studies have shown that polyclonal B cells in the blood of individuals living in malaria-endemic areas comprise of a high level of “atypical” memory B cells which express Fc receptor-like 5 (FCRL5) protein [86]. Not only the expression of this protein but atypical memory B cells also lack expression of classical cell markers of memory B cells such as CD21 and CD27 [87, 88]. Most importantly, unlike classical B cells, these cells have reduced B-cell receptor signaling, decreased effector function, and do not respond to polyclonal stimuli by secreting antibody [87]. Despite these findings, the exact relevance of the presence of atypical B cells remains yet to be fully understood. Another prominent reason associated with the decline of adaptive immunity to malaria is the rapid decay of many malaria-specific antibodies [89]. The acquisition of memory B cells that produce these antibodies is slow since malaria induces immune response that is skewed toward a Th1 response instead of the production of T follicular helper cells. T follicular helper cells are critical for memory B-cell function [90]. Considering malaria-specific memory B cells take many years to develop, rapid decline in antibodies produced by these cells represents a major drawback in the development of better immunity against malaria [91]. Lastly, concurrent interaction of T cells with programmed cell death-1 has also been proposed to result in loss of immunity to malaria. To clarify, this interaction triggers an inhibitory signal in lymphocytes, reduces T-cell function, and leads to cellular exhaustion [92]. Subsequently, this process results in a decline in a long-­ term protective immune response to malaria [93].

Malaria: Cellular Understanding of Disease

31

4 The Role of Immune Response in the Pathogenesis of Cerebral Malaria As described in preceding sections of this chapter, certain parasite-specific or disease-­specific proteins trigger immune responses that are generally aimed at reducing parasitemia or complete clearance of the parasite. Not only do host immune responses change the course of the disease peripherally but also contribute significantly to the pathogenesis of cerebral malaria [94]. Like many other infections, immune cells and soluble inflammatory mediators such as cytokines and chemokines contribute to the disease complications [95]. Subsequent to the establishment of a liver infection, liver cells activate interferon regulatory factors, which in turn induce the transcription of type I IFN. The mounting of type I IFN response leads to the primary activation of IFN-γ-producing natural killer cells with subsequent induction of the secretion of MIG/CXCL9 and IP-10/ CXCL10 from endothelial cells [96]. Following the progression of the infection to the blood stage, dendritic cells recognize infected erythrocytes and induce TNF and IL-12 secretion [97]. IL-12 in turn contributes to further activation of and differentiation of NK and Th1 cells, respectively [67]. On the other hand, TNF and IFN-γ activate the transcription of chemokines and the expression of adhesion molecules on endothelial cells [98]. During the progression of the infection, endothelial cells recognize infected erythrocytes and induce the expression of MCP-1/CCL2 and IL8/CXCL8 chemokines [99]. Given the above occurrence, monocytes, macrophages, neutrophils, and T cells are recruited, resulting in the initiation of a local inflammatory response [100, 101]. Moreover, the secretion of chemokines by these immune cells leads to amplification of the initial inflammatory response resulting in more leukocyte recruitment and increased intensity of the local inflammatory response. In addition, phagocytosis of merozoites by endothelial cells and the release of parasite-specific proteins during schizont rupture lead to presentation of parasite antigens to CD8+ T cells [102]. Consequently, this may facilitate targeted elimination of antigen-presenting endothelial cells, thus causing destruction to the endothelial lining of the blood-brain barrier. Furthermore, this destruction is aggravated by extracellular vesicle-derived miRNAs and chemokine-mediated opening of tight junctions within the blood-brain barrier [103]. Thus, small molecules gain easy access to the brain parenchyma and potentially activate brain-resident microglia and astrocytes. This further amplifies local inflammation and impairs neuronal functionality [104]. In addition to the chemokines IP-10/CXCL10 and PF4/CXCL4, other potential biomarkers that may be useful in the diagnosis and determination of prognosis of cerebral malaria have been identified in several clinical studies [32]. These biomarkers include P. falciparum histidine-rich protein 2 (PfHRP2) and angiopoietin-1 and angiopoietin-2. The latter regulate the activation of endothelial cells, whereas the former is a protein that correlates with parasite biomass [105]. Admittedly, more robust clinical studies are needed to delineate the association between distinct clusters of markers and disease severity. This will aid in the identification of patients at

32

A. D. Forkuo and K. O. Yeboah

risk of developing cerebral malaria early during the disease course and also in the designing of novel evidence-based malaria intervention strategies.

5 Protective Autoimmunity in Malaria Infection Studies investigating the role of autoantibodies in malaria infections have shown that these molecules may exert a dual nature by contributing to the disease or protection against the disease [106]. To illustrate, findings from multiple studies have indicated the association of antibodies such as anti-phosphatidylserine antibody, IgM, and voltage-gated calcium channels autoantibodies with severe clinical developments such as anemia, renal dysfunction, and cerebral malaria, respectively [107–109]. Conversely, other studies have also shown that self-reactive immunoglobulins such as IgE autoantibodies produced against 14-3-3 ε brain protein, a protein responsible for the induction of apoptosis in brain cells, also mediate protection against the infection [110]. In addition to these autoantibodies, several others have been identified to play significant roles, especially in P. falciparum and P. vivax infections (summarized in Table 1). In spite of the availability of several studies aimed at identifying different autoantibodies and their associate with clinical outcomes, little is known about their Table 1  Role of autoantibodies in P. falciparum and P. vivax malaria Autoantibody Beta tubulin III

Erythrocyte band 3 protein

Lipids Non-erythroid alpha spectrin

Nucleic acids Spectrin

Triosephosphate isomerase

Possible mechanism of action Disruption of cytoplasm microtubule

Clinical outcome Protection against P. falciparum-induced cerebral malaria Increases rigidity of noninfected Predisposition to infection red blood cells caused by P. vivax Inhibition of parasite growth and Protection against P. cytoadherence (in vitro) by P. falciparum malaria falciparum Immune complex deposition in Renal failure in P. kidneys falciparum infection Disruption of brain cells Predisposition to P. cytoskeleton falciparum-induced Complement activation and cerebral malaria amplification of neuronal damage Immune complex deposition in Renal failure in P. kidneys falciparum infection Disruption of the cytoskeleton Predisposition to anemia in of red blood cells and P. vivax malaria amplification Of red blood cell damage In vitro lysis of red blood cells Predisposition to anemia in and activation of complement P. falciparum malaria

References [111]

[112] [113]

[114] [115]

[114] [112]

[116]

Malaria: Cellular Understanding of Disease

33

respective epitopes. Identification of these molecules may contribute to the elimination of pathogenic autoantibodies from circulation, thus minimizing or inhibiting their pathogenic effects in host cells [106].

6 Cellular Response to Malaria Vaccines Over the years, many biologically derived antimalarial vaccine candidates have been developed (Table  2). Owing to the difficulties in cloning and expression of Plasmodium antigens, the design of malaria vaccines against blood stages of the parasite has mostly focused on a narrow range of recombinant subunit antigens [117]. The selection of any of the subunit antigens in vaccine development is dependent on their predicted biological function and also on the evidence that antibody response to the subunit offers protective immunity against malaria infection [118]. It has been shown that protective immunity to viral and bacterial infections often lasts long and can be achieved by a number of vaccine formulations without the need of a booster dose. After the inflection point, defined as the level at which antibody titers stabilize after an initial rise following immunization, antibody titers slowly decline [119]. With the currently available effective vaccines used against bacterial and viral infections, their protective thresholds occur well below the inflection point of the vaccines [120]. Thus, raising the vaccine inflection point and/or reducing the rate of antibody response decay may serve as strategies for boosting the effectiveness of malaria vaccines that target preerythrocytic stages of the parasite’s life cycle [119]. The advancement of knowledge in the life cycle of Plasmodium parasite has led to the development of several vaccines, most of which are in clinical trials (Table 2). Among these vaccine candidates, RTS,S is by far the most advanced malaria vaccine candidate. RTS,S is a subunit vaccine that aims at inducing circumsporozoite protein-specific antibodies and thus prevents sporozoites from reaching the liver [121]. Immunologic studies have shown that the protection offered by RTS,S may be strongly attributed to the high titer of anti-CS IgG and induction of circumsporozoite protein-specific Th1 cells. The induction of CD4+ IFNγ T-cell responses is however modest and that of CD8 is low or absent. Thus, the best approach to obtaining better circumsporozoite protein-mediated protection would be to utilize a prime-­ boost combination of RTS,S/AS01 and a CD8-inducing circumsporozoite protein vaccine [122]. This approach has given rise to the adenovirus 35 CS/RTS,S prime-­ boost combinations. In addition to the abovementioned preerythrocytic vaccines, other vaccine types that target preerythrocytic stages of the parasite include AdCh63/MVA ME-TRAP and PfSPZ vaccines. The former is a prime boost sequence of simian adenovirus (AdCh63) that encodes for thrombospondin-related adhesive protein conjugated to a multi-epitope (ME-TRAP), boosted with modified vaccinia virus Ankara (MVA). This vaccine is associated with strong and long-lasting induction of CD8+ T-cell responses [122]. PfSPZ, on the other hand, is a metabolically active, nonreplicating

34

A. D. Forkuo and K. O. Yeboah

Table 2  Stage-specific malaria vaccines currently in clinical trials Phase of trial

Vaccine Preerythrocytic stage RTS,S/AS01

Target

Type of immunity

Circumsporozoite protein

Abs > CD4+ T cells

RTS,S/AS01 fractional dose Genetically attenuated sporozoites CVac

Circumsporozoite protein

Abs > CD4+ T cells

Whole sporozoites

Phase I

PfSPZ

Whole sporozoites

R21/ME–TRAP

TRAP, STARP, LSA1, CSP, LSA3, pb9, EXP1

(γδ, CD8+, CD4+ cells) > Abs (γδ, CD8+, CD4+ cells) > Abs (γδ, CD8+, CD4+ cells) > Abs Abs, T cells (CD8+, CD4+) Abs Abs Abs Abs Abs > T cells

Phase IIb Phase Ib Phase IIb Phase Ib Phase Ia

Abs Abs Abs

Phase Ia Phase Ia Phase Ia

Whole sporozoites

Blood-stage vaccines GMZ2 GLURP MSP3 pfAMA1-DiCO AMA1 MSP3 MSP3 PRIMVAC Var2CSA CHAd63RH5/MVARH5 RH5 Transmission-blocking vaccines Pfs25 VLP Pfs25 Pfs25-EPA/Pfs230-EPA Pfs25, Pfs230 ChAd63 Pfs25/ Pfs25 MVA-Pfs25

Phase IV rollout Phase IIb

Phase I Phase I/IIb Phase Ib

Adapted from WHO Malaria Vaccine Rainbow Tables [125] and Cockburn and Seder [119], kindly also check clinical.gov for more candidates Abs antibodies; MSP-3 merozoite surface protein 3

malaria sporozoite vaccine comprising of sterile, cryopreserved radiation-­attenuated sporozoites [119]. The vaccine is designed to achieve sterilizing immunity but fails to do so due to limitations associated with its manufacturing and scaling up, dosage, and administration methods. The effectiveness of this vaccine is also limited by logistics needed for delivery, since the vaccine requires cryopreservation in liquid nitrogen [122]. Other preerythrocytic vaccines include polyepitope DNA EP1300 vaccine and genetically attenuated sporozoites (Table 2). As discussed earlier, antigens expressed during erythrocytic stages of the parasite and also on infected red blood cells can trigger immune response aimed at reducing parasitemia. This together with the findings that immunoglobulin transfer from immunized adults to children with acute malaria reduces severity of infection has informed the design of various vaccine strategies targeted at erythrocytic stages of Plasmodium parasite [123]. However, polymorphisms in merozoite surface antigens present a major challenge to vaccines that target blood-stage antigens [122]. Examples of blood-stage-specific vaccine strategies include the use of AdCh63/

Malaria: Cellular Understanding of Disease

35

MVA MSP1, a prime boost strategy that strongly induces CD4+ and CD8+ T cell, IgG to some extent [92]. Another erythrocytic stage vaccine, merozoite surface protein 3 (MSP3) vaccine, which targets MSP3 protein elicits variable IgG cytophilic humoral responses [124].

7 Conclusion Naturally acquired immunity against malaria occurs inefficiently, and protection is relatively short-lived. However, the liver and blood stages of the disease comprise a wide array of effector mechanisms that can be exploited to achieve efficient immunity against malaria infection. Complete elucidation of immune effector mechanisms involved in the development of immunity against preerythrocytic and erythrocytic forms of Plasmodium will aid in the development of vaccines that can effectively reduce malaria-related morbidity and mortality. In recent years, many biologically derived antimalarial vaccine candidates have been developed based on some of these effector mechanisms. The design of these vaccines has focused mainly on a narrow range of recombinant subunit antigens, the selection of which is dependent on the predicted biological function. In addition, antibody response to the subunit must offer protective immunity against malaria infection. It is important to note that polymorphisms in merozoite surface antigen are a major challenge that impedes the development of vaccines that target antigens expressed during the erythrocytic stage of Plasmodium.

References 1. Annan K. In-host analysis of malaria dynamics in humans. Open J Appl Sci. 2020;10:191–209. https://doi.org/10.4236/ojapps.2020.105015. 2. Day KP, Artzy-Randrup Y, Tiedje KE, Rougeron V, Chen DS, Rask TS, Rorick MM, Migot-­ Nabias F, Deloron P, Luty AJ, Pascual M. Evidence of strain structure in Plasmodium falciparum var gene repertoires in children from Gabon, West Africa. Proc Natl Acad Sci. 2017;114(20):E4103–11. 3. Sun T, Holowka T, Song Y, Zierow S, Leng L, Chen Y, Xiong H, Griffith J, Nouraie M, Thuma PE, Lolis E, Janse CJ, Gordeuk VR, Augustijn K, Bucala R.  A Plasmodium-­ encoded cytokine suppresses T-cell immunity during malaria. Proc Natl Acad Sci U S A. 2012;109(31):E2117–26. https://doi.org/10.1073/pnas.1206573109. 4. Bansal GP, Kumar N. Immune responses in malaria transmission. Curr Clin Microbiol Rep. 2018;5(1):38–44. 5. López C, Yepes-Pérez Y, Hincapié-Escobar N, Díaz-Arévalo D, Patarroyo MA.  What is known about the immune response induced by Plasmodium vivax malaria vaccine candidates? Front Immunol. 2017;8:126. https://doi.org/10.3389/fimmu.2017.00126. 6. Belachew EB. Immune response and evasion mechanisms of Plasmodium falciparum parasites. J Immunol Res. 2018:6529681. https://doi.org/10.1155/2018/6529681. 7. Vaughan AM, Aly AS, Kappe SH. Malaria parasite pre-erythrocytic stage infection: gliding and hiding. Cell Host Microbe. 2008;4(3):209–18. https://doi.org/10.1016/j.chom.2008. 08.010.

36

A. D. Forkuo and K. O. Yeboah

8. Epiphanio S, Mikolajczak SA, Goncalves LA, Pamplona A, Portugal S, Albuquerque S, Goldberg M, Rebelo S, Anderson DG, Akinc A, Vornlocher HP, Kappe SH, Soares MP, Mota MM.  Heme oxygenase-1 is an anti-inflammatory host factor that promotes murine Plasmodium liver infection. Cell Host Microbe. 2008;3(5):331–8. https://doi.org/10.1016/j. chom.2008.04.003. 9. Götz A, Ty M, Chora Z-LAF, Mota MM, Rodriguez A. Innate immunity to malaria. In: Mota MM, Rodriguez A, editors. Malaria. Springer; 2017. https://doi.org/10.1007/978-­3-­319-­45210-­4. 10. Abuga KM, Jones-Warner W, Hafalla JR.  Immune responses to malaria pre-erythrocytic stages: Implications for vaccine development. Parasite Immunol. 2021;43:e12795. https:// doi.org/10.1111/pim.12795. 11. Casares S, Richie TL. Immune evasion by malaria parasites: a challenge for vaccine development. Curr Opin Immunol. 2009;21(3):321–30. 12. White MT, Bejon P, Olotu A, Griffin JT, Riley EM, Kester KE, et  al. The relationship between RTS, S vaccine-induced antibodies, CD4(+) T cell responses and protection against Plasmodium falciparum infection. PLoS One. 2013;8:e61395. 13. Kurup SP, Butler NS, Harty JT.  T cell-mediated immunity to malaria. Nat Rev Immunol. 2019;19:457–71. 14. Kurup SP, Anthony SM, Hancox LS, Vijay R, Pewe LL, Moioffer SJ, et al. Monocyte-derived CD11c(+) cells acquire Plasmodium from hepatocytes to prime CD8 T cell immunity to liver-stage malaria. Cell Host Microbe. 2019;25:565–77. 15. Stegmann KA, De Souza JB, Riley EM. IL-18-induced expression of high-affinity IL-2R on murine NK cells is essential for NK-cell IFN-gamma production during murine Plasmodium yoelii infection. Eur J Immunol. 2015;45:3431–40. 16. Horowitz A, Hafalla JC, King E, Lusingu J, Dekker D, Leach A, et al. Antigen-specific IL-2 secretion correlates with NK cell responses after immunization of Tanzanian children with the RTS, S/AS01 malaria vaccine. J Immunol. 2012;188:5054–62. 17. Burrack KS, Hart GT, Hamilton SE. Contributions of natural killer cells to the immune response against Plasmodium. Malar J. 2019;18:321. https://doi.org/10.1186/s12936-­019-­2953-­1. 18. Peymanfar Y, Taylor-Robinson AW. Plasmodium sexual stage parasites present distinct targets for malaria transmission-blocking vaccine design. Int J Vaccines Immun. 2016;2(1):51–6. 19. Golgi C.  Sulle febbri malariche estivo-autunnali di Roma. Gazzetta Medica di Pavia. 1893;2(2):481–93; 505–520; 553–559 20. Schofield L, Hackett F. Signal transduction in host cells by a glycosylphosphatidylinositol toxin of malaria parasites. J Exp Med. 1993;177(1):145–53. 21. Bautista JM, Marin-Garcia P, Diez A, Azcarate IG, Puyet A. Malaria proteomics: insights into the parasite-host interactions in the pathogenic space. J Proteome. 2014;97:107–25. https:// doi.org/10.1016/j.jprot.2013.10.011. 22. Krishnegowda G, Hajjar AM, Zhu J, Douglass EJ, Uematsu S, Akira S, Woods AS, Gowda DC. Induction of proinflammatory responses in macrophages by the glycosylphosphatidylinositols of Plasmodium falciparum: cell signaling receptors, glycosylphosphatidylinositol (GPI) structural requirement, and regulation of GPI activity. J Biol Chem. 2005;280(9):8606–16. https://doi.org/10.1074/jbc.M413541200. 23. Orengo JM, Leliwa-Sytek A, Evans JE, Evans B, van de Hoef D, Nyako M, Day K, Rodriguez A. Uric acid is a mediator of the Plasmodium falciparum-induced inflammatory response. PLoS One. 2009;4(4):e5194. 24. van de Hoef DL, Coppens I, Holowka T, Ben Mamoun C, Branch O, Rodriguez A. Plasmodium falciparum-derived uric acid precipitates induce maturation of dendritic cells. PLoS One. 2013;8(2):e55584. https://doi.org/10.1371/journal.pone.0055584. 25. Martinon F, Petrilli V, Mayor A, Tardivel A, Tschopp J. Gout-associated uric acid crystals activate the NALP3 inflammasome. Nature. 2006;440(7081):237–41. 26. Guermonprez P, Helft J, Claser C, Deroubaix S, Karanje H, Gazumyan A, Darasse-Jeze G, Telerman SB, Breton G, Schreiber HA, Frias-Staheli N, Billerbeck E, Dorner M, Rice CM, Ploss A, Klein F, Swiecki M, Colonna M, Kamphorst AO, Meredith M, Niec R, Takacs C,

Malaria: Cellular Understanding of Disease

37

Mikhail F, Hari A, Bosque D, Eisenreich T, Merad M, Shi Y, Ginhoux F, Renia L, Urban BC, Nussenzweig MC.  Inflammatory Flt3l is essential to mobilize dendritic cells and for T cell responses during Plasmodium infection. Nat Med. 2013;19(6):730–8. https://doi. org/10.1038/nm.3197. 27. Sarma PS, Mandal AK, Khamis HJ. Allopurinol as an additive to quinine in the treatment of acute complicated falciparum malaria. Am J Trop Med Hyg. 1998;58(4):454–7. 28. Akhouri RR, Sharma A, Malhotra P, Sharma A.  Role of Plasmodium falciparum thrombospondin-­related anonymous protein in host cell interactions. Malar J. 2008;7:63. 29. Risco-Castillo V, Topcu S, Marinach C, et al. Malaria sporozoites traverse host cells within transient vacuoles. Cell Host Microbe. 2015;18(5):593–603. 30. Liehl P, Zuzarte-Luis V, Chan J, Zillinger T, Baptista F, Carapau D, Konert M, Hanson KK, Carret C, Lassnig C, Muller M, Kalinke U, Saeed M, Chora AF, Golenbock DT, Strobl B, Prudencio M, Coelho LP, Kappe SH, Superti-Furga G, Pichlmair A, Vigario AM, Rice CM, Fitzgerald KA, Barchet W, Mota MM.  Host-cell sensors for Plasmodium activate innate immunity against liver-stage infection. Nat Med. 2014;20(1):47–53. https://doi.org/10.1038/ nm.3424. 31. Miller JL, Sack BK, Baldwin M, Vaughan AM, Kappe SH.  Interferon-mediated innate immune responses against malaria parasite liver stages. Cell Rep. 2014;7(2):436–47. https:// doi.org/10.1016/j.celrep.2014.03.018. 32. Dunst J, Kamena F, Matuschewski K. Cytokines and chemokines in cerebral malaria pathogenesis. Front Cell Infect Microbiol. 2017;7:324. https://doi.org/10.3389/fcimb.2017.00324. 33. Furuta T, Kikuchi T, Iwakura Y, Watanabe N. Protective roles of mast cells and mast cell-­ derived TNF in murine malaria. J Immunol. 2006;177(5):3294–302. 34. Mahanta A, Kar SK, Kakati S, Baruah S.  Heightened inflammation in severe malaria is associated with decreased IL-10 expression levels and neutrophils. Innate Immun. 2015;21(5):546–52. https://doi.org/10.1177/1753425914561277. 35. Tangteerawatana P, Krudsood S, Kanchanakhan N, Troye-Blomberg M, Khusmith S. Low monocyte to neutrophil ratio in peripheral blood associated with disease complication in primary Plasmodium falciparum infection. Southeast Asian J Trop Med Public Health. 2014;45(3):517–30. 36. Pierrot C, Adam E, Hot D, Lafitte S, Capron M, George JD, Khalife J. Contribution of T cells and neutrophils in protection of young susceptible rats from fatal experimental malaria. J Immunol. 2007;178(3):1713–22. 37. Schumak B, Klocke K, Kuepper JM, Biswas A, Djie-Maletz A, Limmer A, van Rooijen N, Mack M, Hoerauf A, Dunay IR. Specific depletion of Ly6Chi inflammatory monocytes prevents immunopathology in experimental cerebral malaria. PLoS One. 2015;10(4):e0124080. https://doi.org/10.1371/journal.pone.0124080. 38. Ayi K, Patel SN, Serghides L, Smith TG, Kain KC.  Nonopsonic phagocytosis of erythrocytes infected with ring-stage Plasmodium falciparum. Infect Immun. 2005;73(4):2559–63. https://doi.org/10.1128/IAI.73.4.2559-­2563.2005. 39. Bettiol E, Van de Hoef DL, Carapau D, Rodriguez A.  Efficient phagosomal maturation and degradation of Plasmodium-infected erythrocytes by dendritic cells and macrophages. Parasite Immunol. 2010;32(6):389–98. https://doi.org/10.1111/j.1365-­3024.2010.01198.x. 40. Fernandez-Arias C, Lopez JP, Hernandez-Perez JN, Bautista-Ojeda MD, Branch O, Rodriguez A. Malaria inhibits surface expression of complement receptor 1 in monocytes/macrophages, causing decreased immune complex internalization. J Immunol. 2013;190(7):3363–72. 41. Osier FH, Feng G, Boyle MJ, et al. Opsonic phagocytosis of Plasmodium falciparum merozoites: mechanism in human immunity and a correlate of protection against malaria. BMC Med. 2014;12:108. 42. Steinman RM. Decisions about dendritic cells: past, present, and future. Annu Rev Immunol. 2012;30:1–22. https://doi.org/10.1146/annurev-­immunol-­100311-­102839. 43. Roussilhon C, Agrapart M, Ballet JJ, Bensussan A.  T lymphocytes bearing the gamma delta T cell receptor in patients with acute Plasmodium falciparum malaria. J Infect Dis. 1990;162(1):283–5.

38

A. D. Forkuo and K. O. Yeboah

44. Costa G, Loizon S, Guenot M, Mocan I, Halary F, de Saint-Basile G, Pitard V, Dechanet-­ Merville J, Moreau JF, Troye-Blomberg M, Mercereau-Puijalon O, Behr C.  Control of Plasmodium falciparum erythrocytic cycle: γδ T cells target the red blood cell-invasive merozoites. Blood. 2011;118(26):6952–62. https://doi.org/10.1182/blood-­2011-­08-­376111. 45. Inoue S, Niikura M, Takeo S, Mineo S, Kawakami Y, Uchida A, Kamiya S, Kobayashi F. Enhancement of dendritic cell activation via CD40 ligand-expressing gammadelta T cells is responsible for protective immunity to Plasmodium parasites. Proc Natl Acad Sci U S A. 2012;109(30):12129–34. https://doi.org/10.1073/pnas.1204480109. 46. Weidanz WP, LaFleur G, Brown A, Burns JM Jr, Gramaglia I, van der Heyde HC. Gammadelta T cells but not NK cells are essential for cell-mediated immunity against Plasmodium chabaudi malaria. Infect Immun. 2010;78(10):4331–40. https://doi.org/10.1128/IAI.00539-­10. 47. Andrade BB, Reis-Filho A, Souza-Neto SM, Clarêncio J, Camargo LMA, Barral A, Barral-­ Netto M. Severe Plasmodium vivax malaria exhibits marked inflammatory imbalance. Malar J. 2010;9:13. https://doi.org/10.1186/1475-­2875-­9-­13. 48. Maneerat Y, Pongponratn E, Viriyavejakul P, Punpoowong B, Looareesuwan S, Udomsangpetch R. Cytokines associated with pathology in the brain tissue of fatal malaria. Southeast Asian J Trop Med Public Health. 1999;30:643–9. 49. Rockett KA, Awburn MM, Aggarwal BB, Cowden WB, Clark IA.  In vivo induction of nitrite and nitrate by tumor necrosis factor, lymphotoxin, and interleukin-1: possible roles in malaria. Infect Immun. 1992;60:3725–30. 50. Kwiatkowski D, Sambou I, Twumasi P, Greenwood BM, Hill AVS, Manogue KR, Cerami A, Castracane J, Brewster DR. TNF concentration in fatal cerebral, non-fatal cerebral, and uncomplicated Plasmodium falciparum malaria. Lancet. 1990;336:1201–4. https://doi. org/10.1016/0140-­6736(90)92827-­5. 51. Ribeiro BP, Cassiano GC, de Souza RM, Cysne DN, Grisotto MAG, de Azevedo Dos Santos APS, Marinho CRF, Machado RLD, Nascimento FRF. Polymorphisms in Plasmodium vivax circumsporozoite protein (CSP) influence parasite burden and cytokine balance in a pre-­ amazon endemic area from Brazil. PLoS Negl Trop Dis. 2016;10:e0004479. https://doi. org/10.1371/journal.pntd.0004479. 52. van Hensbroek MB, Palmer A, Onyiorah E, Schneider G, Jaffar S, Dolan G, Memming H, Frenkel J, Enwere G, Bennett S, Kwiatkowski D, Greenwood B. The effect of a monoclonal antibody to tumor necrosis factor on survival from childhood cerebral malaria. J Infect Dis. 1996;174:1091–7. https://doi.org/10.1093/infdis/174.5.1091. 53. Adachi K, Tsutsui H, Kashiwamura S, Seki E, Nakano H, Takeuchi O, Takeda K, Okumura K, Van Kaer L, Okamura H, Akira S, Nakanishi K. Plasmodium berghei infection in mice induces liver injury by an IL-12- and toll-like receptor/myeloid differentiation factor 88-dependent mechanism. J Immunol. 2001;167:5928–34. 54. Luty AJ, Perkins DJ, Lell B, Schmidt-Ott R, Lehman LG, Luckner D, Greve B, Matousek P, Herbich K, Schmid D, Weinberg JB, Kremsner PG. Low interleukin-12 activity in severe Plasmodium falciparum malaria. Infect Immun. 2000;68:3909–15. 55. Bousema T, Drakeley C.  Epidemiology and infectivity of Plasmodium falciparum and Plasmodium vivax gametocytes in relation to malaria control and elimination. Clin Microbiol Rev. 2011;24(2):377–410. https://doi.org/10.1128/CMR.00051-­10. 56. Urban SL, Doll KL, Harty JT.  Mechanisms of Adaptive Immunity to Plasmodium Liver-­ Stage Infection: The Known and Unknown. In: Mota MM, Rodriguez A, editors. Malaria. Springer; 2017. https://doi.org/10.1007/978-­3-­319-­45210-­4. 57. Kebaier C, Voza T, Vanderberg J.  Kinetics of mosquito-injected Plasmodium sporozoites in mice: fewer sporozoites are injected into sporozoite-immunized mice. PLoS Pathog. 2009;5(4):e1000399. 58. Vanderberg JP, Frevert U. Intravital microscopy demonstrating antibody-mediated immobilisation of Plasmodium berghei sporozoites injected into skin by mosquitoes. Int J Parasitol. 2004;34(9):991–6. https://doi.org/10.1016/j.ijpara.2004.05.005.

Malaria: Cellular Understanding of Disease

39

59. Leitner WW, Haraway M, Pierson T, Bergmann-Leitner ES. Role of opsonophagocytosis in immune protection against malaria. Vaccines. 2020;8:264. 60. Morrison C.  Landmark green light for Mosquirix malaria vaccine. Nat Biotechnol. 2015;33(10):1015–6. https://doi.org/10.1038/nbt1015-­1015. 61. Seder RA, Chang LJ, Enama ME, et al. Protection against malaria by intravenous immunization with a nonreplicating sporozoite vaccine. Science. 2013;341(6152):1359–65. https://doi. org/10.1126/science.1241800. 62. Trimnell A, Takagi A, Gupta M, Richie TL, Kappe SH, Wang R.  Genetically attenuated parasite vaccines induce contact-dependent CD8+ T cell killing of Plasmodium yoelii liver tage-infected hepatocytes. J Immunol. 2009;183(9):5870–8. https://doi.org/10.4049/ jimmunol.0900302. 63. Cockburn IA, Amino R, Kelemen RK, Kuo SC, Tse SW, Radtke A, Mac-Daniel L, Ganusov VV, Zavala F, Menard R. In vivo imaging of CD8+ T cell-mediated elimination of malaria liver stages. Proc Natl Acad Sci U S A. 2013;110(22):9090–5. https://doi.org/10.1073/ pnas.1303858110. 64. Schmidt NW, Podyminogin RL, Butler NS, Badovinac VP, Tucker BJ, Bahjat KS, Lauer P, Reyes-Sandoval A, Hutchings CL, Moore AC, Gilbert SC, Hill AV, Bartholomay LC, Harty JT. Memory CD8 T cell responses exceeding a large but definable threshold provide long-­ term immunity to malaria. Proc Natl Acad Sci U S A. 2008;105(37):14017–22. https://doi. org/10.1073/pnas.0805452105. 65. Swain SL, McKinstry KK, Strutt TM.  Expanding roles for CD4+ T cells in immunity to viruses. Nat Rev Immunol. 2012;12(2):136–48. 66. Overstreet MG, Chen Y-C, Cockburn IA, Tse S-W, Zavala F. CD4+ T cells modulate expansion and survival but not functional properties of effector and memory CD8+ T cells induced by malaria sporozoites. PLoS One. 2011;6(1):e15948. https://doi.org/10.1371/journal. pone.0015948. 67. Stevenson MM, Riley EM. Innate immunity to malaria. Nat Rev. 2004;4:169–80. 68. Wykes MN, Stephens R, Cockburn IA.  Adaptive immunity to Plasmodium blood stages. In: Mota MM, Rodriguez A, editors. Malaria. Springer; 2017. https://doi. org/10.1007/978-­3-­319-­45210-­4. 69. Pistone T, Diallo A, Mechain M, Receveur MC, Malvy D. Epidemiology of imported malaria give support to the hypothesis of ‘long-term’ semi-immunity to malaria in sub-Saharan African migrants living in France. Travel Med Infect Dis. 2014;12(1):48–53. https://doi. org/10.1016/j.tmaid.2013.08.006. 70. Cohen S, Mc GI, Carrington S. Gamma-globulin and acquired immunity to human malaria. Nature. 1961;192:733–7. 71. Stephens R, Albano FR, Quin S, Pascal BJ, Harrison V, Stockinger B, Kioussis D, Weltzien HU, Langhorne J. Malaria-specific transgenic CD4+ T cells protect immunodeficient mice from lethal infection and demonstrate requirement for a protective threshold of antibody production for parasite clearance. Blood. 2005;106(5):1676–84. https://doi.org/10.1182/ blood-­2004-­10-­4047. 72. Ndungu FM, Lundblom K, Rono J, Illingworth J, Eriksson S, Farnert A.  Long-lived Plasmodium falciparum specific memory B cells in naturally exposed Swedish travelers. Eur J Immunol. 2013;43(11):2919–29. https://doi.org/10.1002/eji.201343630. 73. Ndungu FM, Olotu A, Mwacharo J, Nyonda M, Apfeld J, Mramba LK, Fegan GW, Bejon P, Marsh K.  Memory B cells are a more reliable archive for historical antimalarial responses than plasma antibodies in no-longer exposed children. Proc Natl Acad Sci U S A. 2012;109(21):8247–52. https://doi.org/10.1073/pnas.1200472109. 74. Chan JA, Fowkes FJ, Beeson JG.  Surface antigens of Plasmodium falciparum-infected erythrocytes as immune targets and malaria vaccine candidates. Cell Mol Life Sci. 2014;71(19):3633–57. https://doi.org/10.1007/s00018-­014-­1614-­3. 75. Chiu CY, Healer J, Thompson JK, Chen L, Kaul A, Savergave L, Raghuwanshi A, Li Wai Suen CS, Siba PM, Schofield L, Mueller I, Cowman AF, Hansen DS. Association of antibod-

40

A. D. Forkuo and K. O. Yeboah

ies to Plasmodium falciparum reticulocyte binding protein homolog 5 with protection from clinical malaria. Front Microbiol. 2014;5:314. https://doi.org/10.3389/fmicb.2014.00314. 76. Fowkes FJ, Richards JS, Simpson JA, Beeson JG. The relationship between anti-merozoite antibodies and incidence of Plasmodium falciparum malaria: a systematic review and meta-­ analysis. PLoS Med. 2010;7(1):e1000218. https://doi.org/10.1371/journal.pmed.1000218. 77. Voss TS, Healer J, Marty AJ, Duffy MF, Thompson JK, Beeson JG, Reeder JC, Crabb BS, Cowman AF. A var gene promoter controls allelic exclusion of virulence genes in Plasmodium falciparum malaria. Nature. 2006;439(7079):1004–8. https://doi.org/10.1038/nature04407. 78. Chan JA, Howell KB, Reiling L, Ataide R, Mackintosh CL, Fowkes FJ, Petter M, Chesson JM, Langer C, Warimwe GM, Duffy MF, Rogerson SJ, Bull PC, Cowman AF, Marsh K, Beeson JG.  Targets of antibodies against Plasmodium falciparum-infected erythrocytes in malaria immunity. J Clin Invest. 2012;122(9):3227–38. https://doi.org/10.1172/JCI62182. 79. Perez-Mazliah D, Ng DH, Freitas do Rosario AP, McLaughlin S, Mastelic-Gavillet B, Sodenkamp J, Kushinga G, Langhorne J.  Disruption of IL-21 signaling affects T cell­B cell interactions and abrogates protective humoral immunity to malaria. PLoS Pathog. 2015;11(3):e1004715. https://doi.org/10.1371/journal.ppat.1004715. 80. Stevenson MM, Tam MF, Belosevic M, van der Meide PH, Podoba JE. Role of endogenous γ interferon in host response to infection with blood-stage Plasmodium chabaudi AS. Infect Immun. 1990;58:3225–32. 81. Pombo DJ, Lawrence G, Hirunpetcharat C, Rzepczyk C, Bryden M, Cloonan N, Anderson K, Mahakunkijcharoen Y, Martin LB, Wilson D, Elliott S, Elliott S, Eisen DP, Weinberg JB, Saul A, Good MF. Immunity to malaria after administration of ultralow doses of red cells infected with Plasmodium falciparum. Lancet. 2002;360:610–7. 82. Rosa TF, Flammersfeld A, Ngwa CJ, Kiesow M, Fischer R, Zipfel PF, Skerka C, Pradel G. The Plasmodium falciparum blood stages acquire factor H family proteins to evade destruction by human complement. Cell Microbiol. 2016;18(4):573–90. https://doi.org/10.1111/cmi.12535. 83. Boyle MJ, Jagannathan P, Bowen K, McIntyre TI, Vance HM, Farrington LA, Greenhouse B, Nankya F, Rek J, Katureebe A, Arinaitwe E, Dorsey G, Kamya MR, Feeney ME. Effector phenotype of Plasmodium falciparum-specific CD4+ T cells is influenced by both age and transmission intensity in naturally exposed populations. J Infect Dis. 2015;212(3):416–25. https://doi.org/10.1093/infdis/jiv054. 84. Jagannathan P, Eccles-James I, Bowen K, Nankya F, Auma A, Wamala S, Ebusu C, Muhindo MK, Arinaitwe E, Briggs J, Greenhouse B, Tappero JW, Kamya MR, Dorsey G, Feeney ME. IFNgamma/IL-10 co-producing cells dominate the CD4 response to malaria in highly exposed children. PLoS Pathog. 2014;10(1):e1003864. https://doi.org/10.1371/journal. ppat.1003864. 85. Safeukui I, Gomez ND, Adelani AA, Burte F, Afolabi NK, Akondy R, Velazquez P, Holder A, Tewari R, Buffet P, Brown BJ, Shokunbi WA, Olaleye D, Sodeinde O, Kazura J, Ahmed R, Mohandas N, Fernandez-Reyes D, Haldar K.  Malaria induces anemia through CD8+ T cell-dependent parasite clearance and erythrocyte removal in the spleen. MBio. 2015;6(1):e02493–14. https://doi.org/10.1128/mBio.02493-­14. 86. Illingworth J, Butler NS, Roetynck S, Mwacharo J, Pierce SK, Bejon P, Crompton PD, Marsh K, Ndungu FM. Chronic exposure to Plasmodium falciparum is associated with phenotypic evidence of B and T cell exhaustion. J Immunol. 2013;190(3):1038–47. https://doi. org/10.4049/jimmunol.1202438. 87. Portugal S, Tipton CM, Sohn H, Kone Y, Wang J, Li S, Skinner J, Virtaneva K, Sturdevant DE, Porcella SF, Doumbo OK, Doumbo S, Kayentao K, Ongoiba A, Traore B, Sanz I, Pierce SK, Crompton PD. Malaria-associated atypical memory B cells exhibit markedly reduced B cell receptor signaling and effector function. elife. 2015;4:e07218. https://doi.org/10.7554/ eLife.07218. 88. Sullivan RT, Kim CC, Fontana MF, Feeney ME, Jagannathan P, Boyle MJ, Drakeley CJ, Ssewanyana I, Nankya F, Mayanja-Kizza H, Dorsey G, Greenhouse B.  FCRL5 delineates functionally impaired memory B cells associated with Plasmodium falciparum exposure. PLoS Pathog. 2015;11(5):e1004894. https://doi.org/10.1371/journal.ppat.1004894.

Malaria: Cellular Understanding of Disease

41

89. Achtman AH, Bull PC, Stephens R, Langhorne J. Longevity of the immune response and memory to blood-stage malaria infection. Curr Top Microbiol Immunol. 2005;297:71–102. 90. Ryg-Cornejo V, Ioannidis LJ, Ly A, Chiu CY, Tellier J, Hill DL, Preston SP, Pellegrini M, Yu D, Nutt SL, Kallies A, Hansen DS.  Severe malaria infections impair germinal center responses by inhibiting T follicular helper cell differentiation. Cell Rep. 2016;14(1):68–81. https://doi.org/10.1016/j.celrep.2015.12.006. 91. Weiss GE, Traore B, Kayentao K, Ongoiba A, Doumbo S, Doumtabe D, Kone Y, Dia S, Guindo A, Traore A, Huang CY, Miura K, Mircetic M, Li S, Baughman A, Narum DL, Miller LH, Doumbo OK, Pierce SK, Crompton PD. The Plasmodium falciparum-specific human memory B cell compartment expands gradually with repeated malaria infections. PLoS Pathog. 2010;6(5):e1000912. https://doi.org/10.1371/journal.ppat.1000912. 92. Sharpe AH, Wherry EJ, Ahmed R, Freeman GJ. The function of programmed cell death 1 and its ligands in regulating autoimmunity and infection. Nat Immunol. 2007;8(3):239–45. https://doi.org/10.1038/ni1443. 93. Tseng SY, Otsuji M, Gorski K, Huang X, Slansky JE, Pai SI, Shalabi A, Shin T, Pardoll DM, Tsuchiya H. B7-DC, a new dendritic cell molecule with potent costimulatory properties for T cells. J Exp Med. 2001;193(7):839–46. 94. Grau GE, Wassmer SC. Pathogenetic immune response in cerebral malaria. In: Mota MM, Rodriguez A, editors. Malaria. Springer; 2017. https://doi.org/10.1007/978-­3-­319-­45210-­4. 95. Grau GE, Hunt NH. Cytokines and some of their effector mechanisms in cerebral malaria pathogenesis. In: Kremsner PG, Hommel M, Krishna S, editors. Encyclopedia of malaria. New York: Springer; 2014. p. 1–11. 96. Liehl P, Zuzarte-Luis V, Chan J, Zillinger T, Baptista F, Carapau D, et al. Host-cell sensors for Plasmodium activate innate immunity against liver-stage infection. Nat Med. 2014;20:47–53. https://doi.org/10.1038/nm.3424. 97. Wu X, Gowda NM, Gowda DC. Phagosomal acidification prevents macrophage inflammatory cytokine production to malaria, and dendritic cells are the major source at the early stages of infection: implication for malaria protective immunity development. J Biol Chem. 2015;290:23135–47. https://doi.org/10.1074/jbc.M115.671065. 98. Griffith JW, Sokol CL, Luster AD.  Chemokines and chemokine receptors: positioning cells for host defense and immunity. Annu Rev Immunol. 2014;32:659–702. https://doi. org/10.1146/annurev-­immunol-­032713-­120145. 99. Tripathi AK, Sha W, Shulaev V, Stins MF, Sullivan DJ Jr. Plasmodium falciparum-infected erythrocytes induce NF-kappaB regulated inflammatory pathways in human cerebral endothelium. Blood. 2009;114:4243–52. https://doi.org/10.1182/blood-­2009-­06-­226415. 100. Renia L, Howland SW, Claser C, Charlotte Gruner A, Suwanarusk R, Hui Teo T, et  al. Cerebral malaria: mysteries at the blood-brain barrier. Virulence. 2012;3:193–201. https:// doi.org/10.4161/viru.19013. 101. Storm J, Craig AG. Pathogenesis of cerebral malaria–inflammation and cytoadherence. Front Cell Infect Microbiol. 2014;4:100. https://doi.org/10.3389/fcimb.2014.00100. 102. Howland SW, Poh CM, Renia L. Activated brain endothelial cells cross-present malaria antigen. PLoS Pathog. 2015;11:e1004963. https://doi.org/10.1371/journal.ppat.1004963. 103. Mantel PY, Hjelmqvist D, Walch M, Kharoubi-Hess S, Nilsson S, Ravel D, et al. Infected erythrocyte-derived extracellular vesicles alter vascular function via regulatory Ago2-miRNA complexes in malaria. Nat Commun. 2016;7:12727. https://doi.org/10.1038/ncomms12727. 104. Combes V, El-Assaad F, Faille D, Jambou R, Hunt NH, Grau GE.  Microvesiculation and cell interactions at the brain-endothelial interface in cerebral malaria pathogenesis. Prog Neurobiol. 2010;91:140–51. https://doi.org/10.1016/j.pneurobio.2010.01.007. 105. Sahu PK, Satpathi S, Behera PK, Mishra SK, Mohanty S, Wassmer SC. Pathogenesis of cerebral malaria: new diagnostic tools, biomarkers, and therapeutic approaches. Front Cell Infect Microbiol. 2015;5:75. https://doi.org/10.3389/fcimb.2015.00075. 106. Mourão LC, Cardoso-Oliveira GP, Braga ÉM. Autoantibodies and Malaria: Where we stand? Insights into pathogenesis and protection. Front Cell Infect Microbiol. 2020;10:262. https:// doi.org/10.3389/fcimb.2020.00262.

42

A. D. Forkuo and K. O. Yeboah

107. Barber BE, Grigg MJ, Piera K, Amante FH, William T, Boyle MJ, et al. Antiphosphatidylserine immunoglobulin M and immunoglobulin G antibodies are higher in vivax than falciparum malaria, and associated with early anemia in both species. J Infect Dis. 2019;220:1435–43. https://doi.org/10.1093/infdis/jiz334. 108. Das BS. Renal failure in malaria. J Vector Borne Dis. 2008;45:83–97. 109. Lang B, Newbold CI, Williams G, Peshu N, Marsh K, Newton CR. Antibodies to voltage-­ gated calcium channels in children with falciparum malaria. J Infect Dis. 2005;191:117–21. https://doi.org/10.1086/426512. 110. Cornell B, Toyo-Oka K. 14-3-3 proteins in brain development: neurogenesis, neuronal migration and neuromorphogenesis. Front Mol Neurosci. 2017;10:318. https://doi.org/10.3389/ fnmol.2017.00318. 111. Bansal D, Herbert F, Lim P, Deshpande P, Bécavin C, Guiyedi V, et al. IgG autoantibody to brain beta tubulin III associated with cytokine cluster-II discriminate cerebral malaria in central India. PLoS One. 2009;4:e8245. https://doi.org/10.1371/journal.pone.0008245. 112. Mourão LC, Baptista RP, Almeida ZB, Grynberg P, Pucci MM, Castro-Gomes T, et al. Anti-­ band 3 and anti-spectrin antibodies are increased in Plasmodium vivax infection and are associated with anemia. Sci Rep. 2018;6:8762. https://doi.org/10.1038/s41598-­018-­27109-­6. 113. Brahimi K, Martins YC, Zanini GM, Ferreira-da-Cruz MF, Daniel-Ribeiro CT. Monoclonal auto-antibodies and sera of autoimmune patients react with Plasmodium falciparum and inhibit its in vitro growth. Mem Inst Oswaldo Cruz. 2011;106:44–51. https://doi.org/10.1590/ s0074-­02762011000900006. 114. Rivera-Correa J, Conroy AL, Opoka RO, Batte A, Namazzi R, Ouma B, et al. Autoantibody levels are associated with acute kidney injury, anemia and post-discharge morbidity and mortality in Ugandan children with severe malaria. Sci Rep. 2019;9:14840. https://doi. org/10.1038/s41598-­019-­51426-­z. 115. Guiyedi V, Chanseaud Y, Fesel C, Snounou G, Rousselle JC, Lim P, et al. Self-reactivities to the non-erythroid alpha spectrin correlate with cerebral malaria in Gabonese children. PLoS One. 2007;2:e389. https://doi.org/10.1371/journal.pone.0000389. 116. Ritter K, Kuhlencord A, Thomssen R, Bommer W. Prolonged haemolytic anaemia in malaria and autoantibodies against triosephosphate isomerase. Lancet. 1993;342:1333–4. https://doi. org/10.1016/0140-­6736(93)92248-­r. 117. Raja AI, Stanisic DI, Good MF. Immune responses to whole-organism blood-stage malaria vaccines. In: Mota MM, Rodriguez A, editors. Malaria. Springer; 2017. https://doi. org/10.1007/978-­3-­319-­45210-­4. 118. Richards JS, Arumugam TU, Reiling L, Healer J, Hodder AN, Fowkes FJ, Cross N, Langer C, Takeo S, Uboldi AD. Identification and prioritization of merozoite antigens as targets of protective human immunity to Plasmodium falciparum malaria for vaccine and biomarker development. J Immunol. 2013;191(2):795–809. https://doi.org/10.4049/jimmunol.1300778. 119. Cockburn IA, Seder RA. Malaria prevention: from immunological concepts to effective vaccines and protective antibodies. Nat Immunol. 2018;19:1199–211. 120. Plotkin SA.  Correlates of protection induced by vaccination. Clin Vaccine Immunol. 2010;17:1055–65. 121. The RTS, S Clinical Trials Partnership. First results of 3 trial of RTS,S/AS01 malaria vaccine in African children. N Engl J Med. 2011;365:1863–75. 122. Schwartz L, et al. A review of malaria vaccine clinical projects based on the WHO rainbow table. Malar J. 2012;11:11. 123. Bouharoun-Tayoun H, Attanath P, Sabchareon A, Chongsuphajaisiddhi T, Druilhe P.  Antibodies that protect humans against Plasmodium falciparum blood stages do not on their own inhibit parasite growth and invasion in vitro, but act in cooperation with monocytes. J Exp Med. 1990;172:1633–41. 124. Lusingu JP, Gesase S, Msham S, Francis F, Lemnge M, Seth M, Sembuche S, Rutta A, Minja D, Segeja MD, Bosomprah S, Cousens S, Noor R, Chilengi R, Druilhe P. Satisfactory safety and immunogenicity of MSP3 malaria vaccine candidate in Tanzanian children aged 12-24 months. Malar J. 2009;8:163. 125. http://www.who.int/immunization/research/development/Rainbow_tables/en/

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat Antimalarial Resistance Chirag A. Patel, Sonal Pande, Priya Shukla, Ketan Ranch, Moawia M. Al-Tabakha, and Sai H. S. Boddu

Abstract Malaria is among the most prevalent parasite infections caused by Plasmodium genus. According to the most recent data available for the year 2020, the disease killed about 627,000 people, the majority (67%) of whom were children under the age of 5. Resistance, notably in Plasmodium falciparum, has been a foremost factor in the doubling of malaria-related child mortality in eastern and southern Africa. Additionally, antimalarial drug resistance is the utmost likely cause of malaria’s global recurrence in the last three decades. Plasmodium falciparum and Plasmodium vivax have been found to be resistant to currently available antimalarial medicines. Plasmodium falciparum parasite has evolved resistance to practically all antimalarial agents in use, while Plasmodium vivax exhibited resistance to primaquine and chloroquine in some areas. Understanding the statistics of distinct classes of antimalarial drug resistance and introducing strategies that can postpone the emergence of resistance are crucial for making predictions on the onset and spread of resistance to existing antimalarial drugs and recently introduced molecules. Furthermore, understanding the mechanism of resistance and finding particular genetic loci linked to this phenotype are critical for antimalarial resistance

C. A. Patel (*) · S. Pande Department of Pharmacology, L. M. College of Pharmacy, Ahmedabad, India P. Shukla Department of Pharmacology, Smt BNB Swaminarayan Pharmacy College, Vapi, India K. Ranch Department of Pharmaceutics and Pharmaceutical Technology, L. M. College of Pharmacy, Ahmedabad, India M. M. Al-Tabakha · S. H. S. Boddu (*) Department of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Ajman University, Ajman, United Arab Emirates Center of Medical and Bio-allied Health Sciences Research, Ajman University, Ajman, United Arab Emirates © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 R. Shegokar, Y. Pathak (eds.), Malarial Drug Delivery Systems, https://doi.org/10.1007/978-3-031-15848-3_3

43

44

C. A. Patel et al.

surveillance and containment. This chapter summarizes the mechanisms and molecular markers of antimalarial drug resistance and emerging strategies to counter its resistance. Keywords  Drug resistance · Antimalarial drugs · Molecular markers · Plasmodium falciparum · Plasmodium vivax · Malaria vaccine

1 Introduction Malaria is among the most prevalent parasite infections caused by Plasmodium genus (i.e., Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, Plasmodium malariae, and Plasmodium knowelsi), which is spread through a mosquito vector’s bite. Despite the knowledge that malaria is preventable and treatable, it continues to have a devastating effect on people’s quality of life and economy all over the world [1]. As per the most recent WHO report, malaria resulted in approximately 241 million infections and 0.627 million deaths in 2020, with the majority of these cases and fatalities occurring in WHO African Region nations [2, 3]. Total resources required to tackle malaria were estimated at US$ 6800 million in 2020 [3, 4]. Among Plasmodium parasites, P. falciparum and Plasmodium vivax are the most common [5]. Malaria prevention, control, and eradication are malaria-endemic nations’ long-term goals (MECs). About every endemic country is presently striving to eliminate malaria, with the ultimate goal of eradicating this deadly illness from the planet. However, antimalarial medication resistance is the foremost obstacle to achieving the goal [3, 4]. The multidrug resistance observed in the forests of Southeast Asia and South America is most likely explained by established and severe drug pressure mixed with inadequate antiparasitic immunity. Nonetheless, resistance levels may vary depending on location and time [6, 7]. The parasite P. falciparum has acquired resistance to practically all presently used antimalarial medicines, whereas P. vivax has shown resistance to chloroquine and primaquine in some areas [6, 7]. The emergence of resistance has been linked to a significant increase in malaria mortality among residents of some endemic areas [6]. Understanding the statistics of distinct classes of antimalarial drug resistance and introducing strategies that can postpone the emergence of resistance are crucial for predicting the onset and spread of resistance to existing antimalarial drugs and recently introduced molecules [8]. Furthermore, understanding the mechanism of resistance and finding particular genetic loci linked to this phenotype are critical for antimalarial resistance surveillance and containment. This chapter summarizes the resistance mechanisms to current antimalarial drugs, molecular marker of antimalarial drug resistance, and emerging strategies to fight against antimalarial resistance.

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

45

2 Spread of Antimalarial Drug Resistance Although southeast Asia’s Greater Mekong Subregion (GMS) only accounts for a minor portion of the worldwide malaria burden, it has been a hotspot for antimalarial drug resistance [9]. The first instances of chloroquine-resistant P. falciparum appeared in the Thai-Cambodian border, and spread of chloroquine-resistant parasites emerged from two centers, South America and Southeast Asia [10, 11]. Within 20 years, chloroquine-resistant P. falciparum had spread throughout the tropical and subtropical regions of the world [12]. Eventually, chloroquine was replaced with sulfadoxine-pyrimethamine to treat chloroquine-resistant P. falciparum; however, sulfadoxine-pyrimethamine resistance developed quickly [13–15]. The global health situation, particularly in sub-Saharan Africa, was serious by the end of the 1990s, with more than three million people dying each year with malaria [16]. Many drugs were developed as alternate agents based on the chemistry of existing drugs. These include chloroquine and quinine analogs such as amodiaquine, mefloquine piperaquine, pyronaridine, and atovaquone [6, 17]. However, drug-resistant parasites were identified against these drugs within a short span of time [17]. Novartis created and introduced artemether and lumefantrine fixed-dose combination, a first artemisinin-based combination treatment (ACT) [18]. The widespread use of this novel medication in South Africa around the year 2000 resulted in an 87.5% reduction in malaria mortality in less than a year [19]. In 2001, WHO advised ACT as first-line therapy for uncomplicated malaria in locations where the parasites were resistant to conventional medications, such as mefloquine [20]. Following the introduction of ACTs, the first reports of P. falciparum resistant to artemisinin were found in western Cambodia in 2006–2007 and then in GMS countries [20–22]. The global distribution of resistant P. falciparum is now varied, reflecting changes in the treatment use and transmitting intensity. In southeast Asia, resistance to ACTs, dihydroartemisinin–piperaquine and artesunate–mefloquine, has also been reported [24–31]. Artemisinin partial resistance (clonal expansion of PfKelch13 mutations) is now identified in African countries such as Rwanda (R561H), Uganda (C469Y and A675V), and the Horn of Africa (R622I). However, PfKelch13 mutations related to artemisinin partial resistance have become common in the GMS [3]. Figure 1 shows the timeline of antimalarial resistance. Antimalarial resistance has slowly emerged in P. vivax and P. ovale, which is usually attributed to smaller parasitic organism count in humans and thus fewer mutation events. For example, P. vivax and Plasmodium ovale have the ability to bypass erythrocyte schizonticides by exoerythrocytic stage in the liver. Chloroquine resistance in P. vivax was first discovered in Australian visitors to Papua New Guinea in the late 1980s, while chloroquine resistance in Plasmodium malariae was discovered in the early 2000s [23–25]. Chloroquine resistance was developed internationally according to the genetic markers found in P. vivax [26]. Global distribution of malarial resistance is shown in Table 1 [27].

Fig. 1  Timeline of antimalarial drug resistance Table 1  Global distribution of drug-resistant malaria [27] Chloroquine-resistant Plasmodium falciparum Chloroquine-resistant Plasmodium falciparum is found in all malarious areas except in the Americas north of the Panama Canal (Mexico, Hispaniola, other Central American countries) and parts of the Middle East

Multidrug-resistant Plasmodium falciparum Multidrug-resistant (chloroquine, sulfadoxine-­pyrimethamine, mefloquine) P. falciparum is found in Southeast Asia along the Thai borders of Myanmar (Burma) and Cambodia, Burma, Vietnam, and in parts of the Amazon basin Artemisinin-resistant P. falciparum is prevalent in western Cambodia, western Thailand, eastern Myanmar, and southern Vietnam, with the recent spread to northeastern Cambodia and southern Laos

Chloroquine-resistant Plasmodium vivax Chloroquine-resistant Plasmodium vivax is found in Papua New Guinea, Irian Jaya, Indonesia, Myanmar, the Solomon Islands, and in countries of South America including Colombia, Brazil, Guyana, and Peru

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

47

3 Mechanism of Antimalarial Drug Resistance WHO defines drug resistance as the “ability of a parasite strain to survive and/or multiply despite the administration and absorption of a drug given in doses equal to or higher than those usually recommended but within tolerance of the subject” [28]. Antimalarial drug resistance ascends due to genetic mutations that occur by a change in single nucleotide polymorphisms or gene amplifications [29]. Table  2 summarizes the mechanism of action and associated genetic markers of antimalarial drug resistance, while Fig. 2 depicts the mechanism of resistance. Certain other factors of concern are overall parasite load, drug of choice for treating the disease, strength of the drug, improper dosing, and counterfeit drugs. These contribute to antimalarial drug resistance and higher risk of recurrence [30, 31].

Table 2  Antimalarial drugs currently in use, mechanism of action, and their associated genetic markers of resistance [27, 74] Drug class and agent Chloroquine

Site of action Digestive vacuoles

Amodiaquine

Digestive vacuoles

Lumefantrine

Digestive vacuoles

Mefloquine

Digestive vacuoles

Quinine

Digestive vacuoles

Pyronaridine

Digestive vacuoles

Molecular markers of resistance (implicated genes and their mutations) Mechanism of action Pfcrt K76T, K76N, K76I Bind to hematin and interfere with the parasite pfmdr1 N86Y detoxifying mechanisms Pfcrt K72T Bind to hematin and interfere with the parasite pfmdr1 N86Y, Y184F, detoxifying mechanisms S1034C, N1042D, D1246Y pfcrt Bind to hematin and interfere with the parasite pfmdr1 N86Y, Y184F, detoxifying mechanisms S1034C, N1042D, D1246Y, Increased pfmdr1 copy number pfcrt K76T, Increased Bind to hematin and interfere with the parasite pfmdr1copy number, detoxifying mechanisms pfmdr1 N86Y pfmdr1 N86Y, Y184F, Bind to hematin and interfere with the parasite S1034C, N1042D, detoxifying mechanisms D1246Y pfmdr6, 7 or 9 Asn repeats pfcrt pfmrp1 Y191H, A437S pfnhe1 Pfcrt K76T Bind to hematin and interfere with the parasite detoxifying mechanisms (continued)

48

C. A. Patel et al.

Table 2 (continued) Drug class and agent Artemether

Site of action Endoplasmic reticulum and vascular structure

Mechanism of action Alkylation of protein and lipid

Endoplasmic reticulum and vascular structure

Alkylation of protein and lipid

Dihydroartemisinin Endoplasmic reticulum and vascular structure

Alkylation of protein and lipid

Artesunate

Piperaquine

Digestive vacuoles Bind to hematin and interfere with the parasite detoxifying mechanisms

Atovaquone

Mitochondria

Proguanil

Cytosol

Pyrimethamine

Cytosol

Sulfadoxine

Cytosol

Doxycycline Clindamycin

Inside apicoplast Inside apicoplast

Inhibition of mitochondrial electron transport Inhibition of dihydrofolate reductase enzyme Inhibition of dihydrofolate reductase enzyme Inhibition of dihydropteroate synthase enzyme Inhibit protein translation Inhibit protein translation

Molecular markers of resistance (implicated genes and their mutations) pfk13 C580Y, R539T, I543T, F446L, N458Y, P547L, R56IH, Y493H pfatp6 A623E, S769N pfk13 C580Y, R539T, I543T, F446L, N458Y, P547L, R56IH, Y493H pfatp6 A623E, S769N pfk13 C580Y, R539T, I543T, F446L, N458Y, P547L, R56IH, Y493H pfatp6 A623E, S769N Increased pfpm2 and pfpm3 copy numbers Pfcrt K76T Pfcytb Y268S/C/N

Pfdhfr S108N, N51I, and C59R Pfdhfr S108N, N51I, and C59R Pfdhps S436F/A, A437G, K540E, A581G, and A613S/T – A point mutation 23s rRNA

3.1 Chloroquine and Related Compounds Since chloroquine’s introduction in the late 1940s, it has been the cornerstone of attempts to treat and manage malaria. The effectiveness, relative safety of prescribed therapeutic dosages and low cost of chloroquine have contributed to its importance [32]. Chloroquine is a diprotic weak base, and at physiological pH, it exists in three forms: unprotonated, monoprotonated, and diprotonated [33]. The only membrane-­ permeable form of chloroquine is uncharged chloroquine, which readily diffuses into the digesting vacuole (DV) of the parasite [34]. Chloroquine molecule become protonated, accumulate into the DV, bind to hematin, and prevent the formation of hemozoin crystal [34–39]. The free hematin appears to interfere with the plasmodium detoxifying mechanisms and eventually results in parasite death [33, 34, 38]. Quinine, chloroquine, amodiaquine, primaquine, mefloquine, quinoline methanols,

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

49

Fig. 2  Mechanisms of resistance to major antimalarial drugs. Heme detoxification in the digestive vacuole, tetrahydrofolate synthesis in the cytosol, and electron transport in the mitochondrion are all often targeted biological pathways. Resistance to 4-aminoquinolines [chloroquine (CQ), amodiaquine (AQ)], aryl-amino alcohols [quinine (QN), lumefantrine (LMF), and mefloquine (MFQ) is mostly determined by point mutations in the transporters pfcrt and pfmdr1. The key marker of parasite resistance to ART is variant forms of K13 (pfK13). Resistance to sulfadoxine (SD) and both pyrimethamine (PM) and proguanil (PG) can be conferred by mutations in two critical enzymes of the folate biosynthesis pathway, dihydropteroate synthetase (DHPS) and dihydrofolate reductase (DHFR). Atovaquone (AVQ) inhibits mitochondrial electron transport, and resistance to the medicine can be conferred by a single point mutation in the cytochrome b subunit (cytb) of the bc1 complex. QND includes 4-aminoquinolines, arylamino alcohols, and Mannich base

quinine (QN), and quinidine (QND) work by these mechanisms [38, 39]. Recent research has revealed that chloroquine-sensitive parasites collect far more chloroquine in the digestive vacuole than chloroquine-resistant variants [35, 37, 40]. Chloroquine-resistant cultures may efflux chloroquine from the digestive vacuole up to 40 times quicker than chloroquine-sensitive strains [35]. Single nucleotide polymorphisms in the pfcrt gene have been linked to the lower chloroquine accumulation in the plasmodium vacuole of resistant strains [40]. Phenotypes found to carry the pfcrt mutation are K76T or K76N or K76I. The mutation of K76T amino acid in pfcrt is believed to interact with positively charged chloroquine. This allows its exit from the vacuole and thus reduces the concentration of chloroquine in the digestive vacuole [41–47]. There are studies which suggest that a single amino acid change S16R will introduce a positive charge in the vacuole and block the leak to restore chloroquine [48, 49]. Amodiaquine, a 4-aminoquinoline chemically similar to chloroquine, has been widely used as a monotherapy and is currently being utilized as a companion agent in ACTs [50, 51]. The single nucleotide polymorphisms

50

C. A. Patel et al.

in Pfcrt and Pfmdr1 are linked with lower sensitivity to chloroquine and amodiaquine [50, 51]. In vitro experiments show that the presence of pfcrt codon 72 to 76 corresponds to significant levels of resistance in desethylamodiaquine [51]. Resistance to mefloquine (4-methanolquinoline) is also mediated by amplification of pfmdr1 [52, 53]. However, mutations in Pfmdr1-N86 variant have been linked to lowered sensitivity to lumefantrine (hydrophobic arylamino alcohol antimalarials) in Africa and Asia [54–56], and single nucleotide polymorphisms at Y191H and A437S in pfmrp were found to be linked with quinine resistance [57]. Furthermore, pfnhe1 mutation may also cause quinine resistance [47].

3.2 Antifolate Compounds Antifolate agents are segmented into two classes, dihydropteroate synthase (DHPS) inhibitors and dihydrofolate reductase (DHFR) inhibitors [58, 59]. These combinations are recommended for the synergistic effect. Inhibition of enzymes can produce a lethal effect on the parasite. Sulfadoxine inhibits the dihydropteroate synthetase (DHPS), whereas proguanil, cycloguanil, and pyrimethamine inhibit dihydrofolate reductase (DHFR) [58, 60, 61]. Pyrimethamine resistance occurs due to mutation at dhfr domain of pfdhfr-ts, at 108, 59, and 51 codons [62]. Similarly, mutation in P. falciparum dihydropteroate synthetase (Pfdhps) gene compromises sulfadoxine at codon A437G/K540E, A437G/A581G, or A437G/K540E/A581G [63].

3.3 Atovaquone Atovaquone is a lipophilic hydroxynaphthoquinone analogue that possesses similar structural properties to coenzyme Q. It hampers the membrane potential by disrupting respiration and pyrimidine biosynthesis. Atovaquone is a competitive inhibitor of ubiquinol and hinders the mitochondrial electron transport chain at bc1 [23]. In comparison with artemisinin and chloroquine, atovaquone exhibits slow parasite death. However, these compounds are active in liver-stage malaria. Mutation at the ubiquinol binding site confers resistance. Y268N/S/C mutations in the codon of the cytb gene are associated with atovaquone resistance, though in combination with proguanil, the resistance is retarded [64, 65].

3.4 Artemisinin Artemisinin is the backbone of antimalarial therapy and has a distinct endoperoxide bridge, which is necessary for its action [66]. The mechanism of artemisinin is unknown, but the prevalent notion is the cleaved endoperoxide bridge, resulting in

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

51

generation of free radicals or reactive oxygen species (ROS) that alkylate important biomolecules [67]. A report revealed that artesunate exerts its antimalarial effect by breaking DNA double strands in P. falciparum by ROS generation. Single nucleotide polymorphisms in pfatp6 and ubp1 have been linked to increased artesunate resistance in French Guyana field isolates and P. chabaudi (rodent malaria parasite), respectively [68, 69]. Furthermore, mutations in the K13 protein’s propeller region at Y493H, R539T, I543T, and C580Y have been identified as a significant predictor of artemether and artesunate resistance in P. falciparum [70]. Artesunate, dihydroartemisinin, and artesunate are prescribed in combination with other antimalarial drugs (i.e., lumefantrine, mefloquine, amodiaquine, sulfadoxine–pyrimethamine, piperaquine, and pyronaridine) to extend the life span of artemisinin therapies by limiting the establishment of resistant plasmodium [20].

3.5 Doxycycline Doxycycline, from the class of tetracycline antibiotics, acts by inhibiting bacterial protein synthesis. Recent studies showed that doxycycline inhibits nucleotides and deoxynucleotides in falciparum. It is used as prophylaxis in regions where there is chloroquine and multidrug-resistant P. falciparum malaria. Resistance to doxycycline has not been reported [71].

3.6 Clindamycin In 1967, clindamycin was first reported to have antimalarial activity and work by binding onto 50s ribosome of P. falciparum [72, 73]. For MDR P. falciparum malaria, a combination of clindamycin with quinine is preferred [74].

4 Molecular Marker of Antimalarial Drug Resistance In the fight against malaria, keeping track of and identifying drug-resistant P. falciparum strains are critical. In vitro and/or in  vivo drug susceptibility testing have traditionally been used to identify resistant parasite strains. These approaches, while useful in detecting resistant strains, are expensive and time-consuming [75]. Identifying the molecular markers (mutations/single nucleotide polymorphism in malaria parasite genomics) of resistance that are associated with resistance to a particular antimalarial drug is another cost-effective, time-saving, high-throughput, and robust method that shows a lot of promise in the identification of resistant parasite strains [75].

52

C. A. Patel et al.

4.1 Molecular Markers for Drug Resistance in P. falciparum 4.1.1  pfcrt Gene The PfCRT belongs to the drug transporter superfamily and is found in the plasmodium DV [43, 47]. Drug susceptibility tests revealed that pfcrt polymorphisms (notably the K76T mutation) have a role in chloroquine resistance, which was later verified as a reliable predictor of chloroquine treatment response [76, 77]. The pfcrt K76T polymorphism has also been considered as an indication of amodiaquine resistance. Other antimalarial medicines, such as halofantrine, mefloquine, lumefantrine, artemisinin, and quinine, are also affected by pfcrt polymorphisms [77, 78]. 4.1.2  pfmdr1 Gene The PfMDR1 is a protein found in the digesting vacuole membrane. Pfmdr1 functions as a general importer, sequestering xenobiotics and medicines into the DV [79]. It may also have an indirect effect on drug flow by influencing intracellular ion gradients such as Cl- or pH. The pfmdr1 gene is linked to antimalarial drug resistance through amplification of pfmdr1 copy number or by single nucleotide polymorphism in the gene. The polymorphisms of pfmdr1 alter the substrate specificity and result in resistance to different antimalarial drugs [81]. The pfmdr1 N86Y polymorphism has been associated with chloroquine and amodiaquine treatment failure, whereas pfmdr1 D1246Y is involved in resistance to amodiaquine and desethylamodiaquine [80]. The pfmdr1 N86-F184-D1246 and pfmdr1 N1042D are linked with resistance to lumefantrine in Africa and Thai-Myanmar border, respectively [82–84]. The pfmdr1 S1034C/N1042D/D1246Y polymorphism is associated with decreased potency of quinine [64]. Amplification of pfmdr1 copy number of pfmdr1 has been linked with reduced sensitivity to dihydroartemisinin, halofantrine, mefloquine, quinine, and artesunate [80]. 4.1.3  pfmrp Gene PfMRP is a protein that regulates transport. Resistance to antimalarial medications such as quinine and chloroquine has been linked to mutations in the pfmrp gene [57]. In Asia and the Americas, Y191H and A437S have been associated with chloroquine resistance, while in the Americas, Y191H and A437S have been linked to quinine resistance. Pfmrp may operate as a secondary determinant in the modulation of parasite resistance to primaquine, piperaquine, and artemisinin [40, 85]. 4.1.4  Pfnhe-1 Gene The pfnhe-1 gene of P. falciparum was discovered on chromosome 13 of the parasite genome. The pfnhe aggressively effluxes protons to keep the parasite’s pH around 7.4 [86]. Increased DNNND repeat number in microsatellite ms4670 has

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

53

been linked to lower quinine sensitivity and might be used as a viable marker for quinine resistance [87]. 4.1.5  pfdhps and pfdhfr Gene Sulfadoxine inhibits pfdhps, and pyrimethamine and cycloguanil have been shown to affect pfdhfr function [88]. Resistance to sulfadoxine-pyrimethamine combination treatment has been linked to point mutations in both pfdhfr and pfdhps. S108N, N51I, C59R, and I164L are important polymorphisms in pfdhfr that cause pyrimethamine resistance, but pfdhfr A16V/S108T confers resistance to cycloguanil [89–91]. Sulfadoxine resistance is significantly linked to the pfdhps S436A/F, A437G, K540E, A581G, and A613S/T polymorphisms [92]. 4.1.6  pfatp6 and Kelch 13 Gene The pfatp6 gene is a molecular marker that has been linked to partial resistance to artemisinin and its derivatives. In D10 parasite strains, pfatp6 L263E mutation has been linked to higher artemisinin and dihydroartemisinin IC50 values. Artemether IC50 values were observed to be high in clinical isolates from France with the pfatp6 S769N mutation [93]. Kelch 13 gene is another gene that has been linked to artemisinin and its derivatives. Y493H, R539T, I543T, F446L, P574L, and C580Y are all mutations in Kelch 13 gene that have been linked to artemisinin resistance [70, 94]. 4.1.7 Pfcytb Gene Atovaquone is a potent inhibitor of cytochrome bc1 complex [95]. Resistance to atovaquone has been linked to pfcytb Y268S/C/N mutations [23]. As a result, the cytochrome b gene can be used as a molecular marker to track atovaquone resistance.

4.2 Molecular Markers for Drug Resistance in P. vivax In P. vivax, orthologs of pfcrt and pfmdr1 have been identified as pvcrt-o and pvmdr1, respectively. Sulfadoxine-pyrimethamine susceptibility has been connected to changes in dhfr and dhps genes in P. vivax, while chloroquine resistance has been linked to P. vivax isolates with pvmdr1 Y976F mutation [96].

5 Emerging Strategies to Combat Antimalarial Resistance Looking at the current scenario, many researchers are recommending artemisinin-­ based combination therapies (ACT) for multiresistant parasites [94, 97]. The emergence and dissemination of resistance to existing therapies indicate the requirement

C. A. Patel et al.

54

for the development of new antimalarial treatments [98]. Ultimately new advancement is introduced for drug discovery, and even older drugs are revived for the development of new antimalarial drugs [99, 100]. A list of antimalarials at different stages of drug discovery and development pipeline is shown in Table 3.

Table 3  Antimalarials at different stages of the drug discovery and development pipeline Name of molecules

Parasitic stage

Mechanism of action

MMV371

Asexual blood stages Asexual blood stages

Selective inhibitor of cytochrome bc1 complex Inhibition of acetylCoA synthetase (acetylCS) Inhibition of Plasmodium falciparum ACS10/11

MMV183

Current status (Phase Therapeutic I/Phase II) indications

Company

Preclinical Prophylaxis of development malaria

Janssen

Preclinical Uncomplicated development malaria and potential for use in severe malaria Preclinical Uncomplicated development malaria treatment and resistance management (TPP-1) Phase I Uncomplicated malaria treatment, resistance management, potential for prophylaxis Phase II b Uncomplicated malaria treatment and resistance management Phase I Intermittent preventive treatment and prophylaxis

TropIQ

GSK701

Asexual blood stages

M5717

Asexual blood stages

P. falciparum EF2 inhibitor novel mechanism of action

ZY19489

Asexual blood stages

Unknown

Atoguanil

Asexual blood stages

MMV533

Asexual blood stages

Interfere with two pathways involved in the biosynthesis of pyrimidines required for nucleic acid replication Acts against P. falciparum via inhibition of mitochondrial electron transport Unknown Phase I

Uncomplicated malaria treatment and resistance management

GSK

Merck KGaA

Zydus Cadila

Ipca

Sanfoi

(continued)

55

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat… Table 3 (continued) Current status (Phase Therapeutic I/Phase II) indications

Name of molecules

Parasitic stage

Mechanism of action

Ganaplacide-­ Lumefantrine

Asexual blood stages

Cipargamin

Asexual blood stages

Decreased Phase IIb susceptibility to ganaplacide is associated with mutations in three P. falciparum genes, CARL (cyclic amine resistance locus), UDP-galactose and acetyl-CoA transporters PfATP4 inhibitor Phase II

Ferroquine Sanofi

Asexual blood stages

DHA-PQP dispersible

Asexual blood stages

Artemether-­ lumefantrine

Asexual blood stages

Sulfadoxine-­ Blood pyrimethamine stage

Primaquine dispersible

Blood stage

Uncomplicated malaria treatment, resistance management, potential for prophylaxis

Company Novartis

Uncomplicated Novartis malaria treatment, resistance management, severe malaria treatment Uncomplicated Sanfoi malaria treatment and resistance management

Ferroquine (FQ), Phase II b belonging to 4-aminoquinolines: inhibition of haem detoxification Inhibit hemozoin Therapeutic 3-day cure, formation confirmatory artemisinin-based combination therapy (dihydroartemisininpiperaquine) Inhibit hemozoin Therapeutic 3-day cure, formation confirmatory artemisinin-based combination therapy (artemether-­ lumefantrine) for patients 5 kg Treatment of uncomplicated malaria caused by P. falciparum or by P. vivax in adults and children ≥20 kg

Universal Corporation

Sulfadoxine-­ Blood pyrimethamine stage

Inhibits the activity Regulatory of dihydropteroate review synthase

Coartem® Dispersible

Blood stage

Prevent hemozoin formation

Approved

Artesun®

Blood stage

Approved

Larinate® 60 mg for injection

Blood stage

Eurartesim®

Blood stage

Generates free radical by endoperoxide bridge formation Generates free radical by endoperoxide bridge formation Generates free radical by endoperoxide bridge formation

Pyramax®

Blood stage

Generates free radical by endoperoxide bridge formation

Company

Regulatory review

Approved

Approved

Approved

Swipha/ Biogaran

Novartis

Fosun Pharma

Ipca

Alfasigma

Shin Poong

(continued)

57

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat… Table 3 (continued) Current status (Phase Therapeutic I/Phase II) indications

Company

Generates free radical by endoperoxide bridge formation

Approved

Shin Poong

Blood stage

Generates free radical by endoperoxide bridge formation

Approved

ASMQ

Blood stage

Generates free radical by endoperoxide bridge formation

Approved

SPAQ-CO™ dispersible

Blood stage

Inhibits the activity Approved of dihydropteroate synthase

Supyra®

Blood stage

Inhibits the activity Approved of dihydropteroate synthase

Artesunate Rectocaps

Blood stage

Generates free radical by endoperoxide bridge formation

Name of molecules

Parasitic stage

Mechanism of action

Pyramax® granules

Blood stage

ASAQ Winthrop®

Approved

For the treatment of uncomplicated malaria infection caused by P. falciparum or P. vivax in children and infants weighing 5 kg to under 20 kg Treatment of uncomplicated P. falciparum malaria in adults, children, and infants >5 kg Treatment of uncomplicated P. falciparum malaria in adults, children, and infants >5 kg Seasonal malaria chemoprevention (SMC) for children 3–59 months in eligible regions (Sahel region in sub-Saharan Africa) Seasonal malaria chemoprevention (SMC) for children 3–59 months in eligible regions (Sahel region in sub-Saharan Africa) Pre-referral emergency intervention for severe P. falciparum malaria in children aged 6 months* (5 kg) to 6 years (20 kg) and >6 h from a treatment center

Sanofi

Cipla

Fosum Pharma

S Kant Healthcare

Cipla

(continued)

58

C. A. Patel et al.

Table 3 (continued) Current status (Phase Therapeutic I/Phase II) indications

Name of molecules

Parasitic stage

Mechanism of action

ArtecapTM

Blood stage

Generates free radical by endoperoxide bridge formation

Kozenis or Krintafel

Blood stage parasite

Eliminates Approved hypnozoites, the dormant liver form of the parasite, after the organisms have been cleared from the bloodstream

Approved

Company

Pre-referral Strides Pharma emergency intervention for severe P. falciparum malaria in children aged 6 months* (5 kg) to 6 years (20 kg) and >6 h from a treatment center Prevention of GSK relapse of P. vivax malaria from 16 years of age

Data sources for this table include the WHO Malaria Vaccine Rainbow Table and Clinicaltrials. gov website

5.1 Advancement on Existing Antimalarial Furtherance on the existing treatment can be established by modifying the dose or combining the drug with another one having different mechanisms of actions [101, 102]. Increasing the total dose of chloroquine given to patients is one potential advancement that can be performed. Another strategic change that can be brought is to maintain a daily dose of the drug course prescribed but extend treatment from 3 days to 5–7 days. Many researchers have gone through a triple-drug combination of various infectious diseases to overcome their resistance. The same concept can be applied over here in malaria, and the usual combination of ACT may also be implemented over here [103]. Piperaquine/dihydroartemisinin, artesunate-mefloquine, piperaquine/dihydroartemisinin plus mefloquine, artemether–lumefantrine, and artemether–lumefantrine plus amodiaquine have all recently been examined in large-scale trials. Another approach to be considered is resistance reversal agents. Here, the resistance of antimalarial drugs is being inhibited with the help of agents, which are likely to reverse the resistance generated by parasites against the agents. Proven resistance reversal agents are calcium channel blockers, chlorpheniramine, and primaquine against P. falciparum to chloroquine [104, 105]. The next strategy can be to reintroduce drugs withdrawn for some years. It has been proven that withdrawal of chloroquine from many countries such as Malawi [106] and Tanzania [107] for a couple of years due to resistance generated and then introducing it again reestablished the potency

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

59

of the drug against parasites. This recovery could aid in the development of chloroquine-based combination medications as an alternative to sulfadoxine-­ pyrimethamine as an intermittent preventive treatment for pregnant women, since the public health benefits are diminishing due to sulfadoxine-pyrimethamine resistance.

5.2 New Drug Discovery and Development Additional approaches to developing strong antimalarial medications include rational targeting of critical parasite activities (target-based) and whole-cell phenotypic screening for chemicals that have desired effect on parasite cells [108]. The crucial targets include metabolite biosynthesis, membrane transport, and signaling system, and the hemoglobin degradation processes [109, 110]. KAI407, 0KAF156, plasmodium phosphatidylinositol-4-OH kinase inhibitors, KAE609, P. falciparum P-type ATPase 4 inhibitors, and DDD107498 are some of the new antimalarial compounds discovered using a cell-based approach [111–113]. In contrast, Plasmodium DHODH inhibitor, DSM265, a compound with multistage antimalarial activity and the inhibitor of DHFR and P218 are the potent parasite inhibitors found from target-­ based screening techniques [114].

5.3 Malaria Vaccine The vaccine is considered to realize malaria eradication apart from traditional antimalarial activity and mosquito control measures. As a result, vaccine development has become a long-term priority for many researchers. Vaccines that target one or more stages of the parasite life cycle are currently being tested. Depending on the stage of the target, there are preerythrocytic vaccinations, blood-stage vaccines, and transmission-blocking vaccines [115]. WHO recommends widespread use of RTS,S/AS01 (RTS,S) malaria vaccine among children in regions with moderate to high P. falciparum malaria transmission. Many next-generation vaccines are in Phase 2 trials, which mainly target all stages of P. falciparum malaria parasite life cycle (Fig. 3, Table 4) [92, 115, 116].

6 Conclusion Although the area of drug research has advanced in recent years, a new effective antimalarial medicine is still required. The use of modern empirical and theoretical research in population genetics can help build a strategy to postpone the calamity caused by drug-resistance evolution against newly launched

C. A. Patel et al.

60

Fig. 3  Life cycle of P. falciparum in human showing blood and liver stages Table 4  Malarial vaccine in clinical development Parasitic stage Name of vaccine Sporozoite Vaccines RTS,S/AS01

Mode of action (inhibition of merozoite invasion)

Current status Type vaccine

(Phase I/ Phase II)

Inhibition of sporozoite infection

Subunit (a recombinant circumsporozoite protein)

RTS,S/AS01 “Fractional Dose”

Inhibition of sporozoite infection

R21/Matrix-M

Inhibition of sporozoite infection and also able to produce antibodies against additional epitopes

Subunit (a recombinant circumsporozoite protein) Subunit (a recombinant circumsporozoite protein)

Pilot implementation (Ghana, Kenya and Malawi since 2019) Phase III

Phase I/IIa and I b

(continued)

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

61

Table 4 (continued) Parasitic stage Name of vaccine R21/AS01

FMP012[PfCeITOS]/ GLA-SE or AS01

Liver-Stage Vaccines PfSpZ vaccine PfGAP3KO PfSPZ-GA1 ChAd63-MVA ME-TRAP

ChAd63 or MVA ME-TRAP (IV route)

ChAdOx1-MVA LS2

Blood-Stage Vaccines PAMVAC/Alhydrogel or GLA-SE or GLA-LSQ

Mode of action (inhibition of merozoite invasion) Inhibition of sporozoite infection Inhibition of sporozoite infection

Killing of infected hepatocytes Killing of infected hepatocytes Killing of infected hepatocytes Killing of infected hepatocytes CD8+T-cell response Killing of infected hepatocytes CD8+T-cell response Killing of infected hepatocytes T-cell targeting immune response

Prevention of Irbc-mediated pathology Block erythrocyte invasion to high efficiency PRIMVAC/Alhydrogel Prevention of or GLA-SE Irbc-mediated pathology Transmission-blocking vaccines ChAd63-MVA Inhibition of sexual Pfs25-IMX313 stage development Pfs25-EPA/Alhydrogel Inhibition of sexual or AS01 stage development Pfs230D1M-EPA/ Inhibition of sexual Alhydrogel or AS01 stage development

Current status Type vaccine (Phase I/ Phase II) Phase I/IIa and I b HBsAg fused to the C-terminus and central repeats of the CSP Phase I/IIa and I b Recombinant subunit protein based on the 3D7 clone of Plasmodium falciparum cell-traversal protein Whole organism (radiation attenuation) Whole organism (genetic attenuation) Whole organism (genetic attenuation) Viral vector vaccine

Phase IIb

Phase IIb

Viral vector vaccine

Phase Ia

Viral vector vaccine

Phase I/IIa

Phase I/IIa Phase I/IIa

Recombinant fragment of Phase Ia/b VAR2CSA

AR2CSA-derived Phase Ia/b placental malaria vaccine

Subunit vaccine

Phase Ia

Subunit vaccine

Phase Ia/b

Subunit vaccine

Phase Ia/b (continued)

C. A. Patel et al.

62 Table 4 (continued) Parasitic stage Name of vaccine Pfs25 VLP-FhCMC/ Alhydrogel ChAd63-MVA RH5 RH5.1/AS01 PfAMA1-DICo/ Alhydrogel or GLA-SE P27A/Alhydrogel or GLA-SE BK-SE36[PfSERA5]/ Alhydrogel ± CpG PfPEBS/ Alhydrogel Vaccines for P. vivax Pvs25H/Alhydrogel

Mode of action (inhibition of merozoite invasion) Inhibition of sexual stage development Inhibition of merozoite invasion Inhibition of merozoite invasion Inhibition of merozoite invasion Inhibition of merozoite invasion Inhibition of merozoite invasion Inhibition of merozoite invasion Inhibition of merozoite invasion

Current status Type vaccine Subunit vaccine

(Phase I/ Phase II) Phase Ia

Subunit vaccine

Phase Ia/b

Subunit vaccine

Phase I/IIa

Subunit vaccine

Phase Ia/b

Subunit vaccine

Phase Ia/b

Subunit vaccine

Phase Ia/b

Subunit vaccine

Phase 1/IIa

Subunit vaccine

Phase II

Data sources for this figure included the WHO Malaria Vaccine Rainbow Table and Clinicaltrials.gov

antimalarial medications. Furthermore, drug research programs may now benefit from the assays available to uncover medications with a more extensive range of activity, which will help to limit disease transmission and resistance spread. Another requirement is the development of quick, dependable diagnostic tools for detecting the existence of mutations imparting medication resistance concurrently with infection diagnosis.

References 1. Rasmussen C, Alonso P, Ringwald P. Current and emerging strategies to combat antimalarial resistance. Expert Rev Anti-Infect Ther. 2021;0(0):1–20. Available from:. https://doi.org/1 0.1080/14787210.2021.1962291. 2. Takumida M, Takumida H, Anniko M.  Localization of histamine (H1, H2, H3 and H4) receptors in mouse inner ear. Acta Otolaryngol. 2016;136(6):537–44. https://doi.org/10.310 9/00016489.2015.1136433. 3. Ippolito MM, Moser KA, Kabuya J-BB, Cunningham C, Juliano JJ.  Antimalarial Drug Resistance and Implications for the WHO Global Technical Strategy. Curr Epidemiol Rep. 2021;8(2):46–62. Available from:. https://doi.org/10.1007/s40471-­021-­00266-­5. 4. Leang R, Taylor WRJ, Bouth DM, Song L, Tarning J, Char MC, et  al. Evidence of Plasmodium falciparum malaria multidrug resistance to Artemisinin and Piperaquine in Western Cambodia: Dihydroartemisinin-Piperaquine Open-Label Multicenter Clinical Assessment. Antimicrob Agents Chemother. 2015;59(8):4719–26. https://doi.org/10.1128/ AAC.00835-­15.

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

63

5. Amelo W, Makonnen E. Efforts made to eliminate drug-resistant malaria and its challenges. Biomed Res Int. 2021;2021:5539544. https://doi.org/10.1155/2021/5539544. 6. Blasco B, Leroy D, Fidock DA. Antimalarial drug resistance: linking Plasmodium falciparum parasite biology to the clinic. Nat Med. 2017;23(8):917–28. https://doi.org/10.1038/nm.4381. 7. Chu CS, White NJ. The prevention and treatment of Plasmodium vivax malaria. PLoS Med. 2021;18(4):e1003561. https://doi.org/10.1371/journal.pmed.1003561. 8. Siddiqui FA, Liang X, Cui L. Plasmodium falciparum resistance to ACTs: emergence, mechanisms, and outlook. Int J Parasitol Drugs Drug Resist. 2021;16:102–18. Available from: https://www.sciencedirect.com/science/article/pii/S2211320721000269 9. Rathmes G, Rumisha SF, Lucas TCD, Twohig KA, Python A, Nguyen M, et al. Global estimation of antimalarial drug effectiveness for the treatment of uncomplicated Plasmodium falciparum malaria 1991–2019. Malar J. 2020;19(1):374. Available from:. https://doi. org/10.1186/s12936-­020-­03446-­8. 10. Moore DV, Lanier JE. Observations on two Plasmodium falciparum infections with an abnormal response to chloroquine. Am J Trop Med Hyg. 1961;10:5–9. https://doi.org/10.4269/ ajtmh.1961.10.5. 11. Harinasuta T, Suntharasamai P, Viravan C.  Chloroquine-resistant falciparum malaria in Thailand. Lancet (London, UK). 1965;2(7414):657–60. https://doi.org/10.1016/ s0140-­6736(65)90395-­8. 12. Payne D.  Spread of chloroquine resistance in Plasmodium falciparum. Parasitol Today. 1987;3(8):241–6. https://doi.org/10.1016/0169-­4758(87)90147-­5. 13. Rønn AM, Msangeni HA, Mhina J, Wernsdorfer WH, Bygbjerg IC. High level of resistance of Plasmodium falciparum to sulfadoxine-pyrimethamine in children in Tanzania. Trans R Soc Trop Med Hyg. 1996;90(2):179–81. https://doi.org/10.1016/s0035-­9203(96)90129-­7. 14. Clyde DF, Shute GT. Resistance of Plasmodium falciparum in Tanganyika to pyrimethamine administered at weekly intervals. Trans R Soc Trop Med Hyg. 1957;51(6):505–13. https:// doi.org/10.1016/0035-­9203(57)90039-­1. 15. Clyde DF.  Observations on monthly pyrimethamine (daraprim) prophylaxis in an East African village. East Afr Med J. 1954;31(2):41–6. 16. Breman JG, Alilio MS, Mills A. Conquering the intolerable burden of malaria: what’s new, what’s needed: a summary. Am J Trop Med Hyg. 2004;71(2 Suppl):1–15. 17. Bosman A, Mendis KN. A major transition in malaria treatment: the adoption and deployment of artemisinin-based combination therapies. Am J Trop Med Hyg. 2007;77(6 Suppl):193–7. 18. Na-Bangchang K, Karbwang J. Pharmacology of antimalarial drugs, current anti-malarials. In: Kremsner PG, Krishna S, editors. Encyclopedia of Malaria. New York: Springer; 2019. p. 1–82. Available from:. https://doi.org/10.1007/978-­1-­4614-­8757-­9_149-­1. 19. Snow RW, Amratia P, Kabaria CW, Noor AM, Marsh K. The changing limits and incidence of malaria in Africa: 1939–2009. Adv Parasitol. 2012;78:169–262. https://doi.org/10.1016/ B978-­0-­12-­394303-­3.00010-­4. 20. Dondorp AM, Nosten F, Yi P, Das D, Phyo AP, Tarning J, et  al. Artemisinin resistance in Plasmodium falciparum malaria. N Engl J Med. 2009;361(5):455–67. https://doi.org/10.1056/ NEJMoa0808859. 21. Rogers WO, Sem R, Tero T, Chim P, Lim P, Muth S, et al. Failure of artesunate-­mefloquine combination therapy for uncomplicated Plasmodium falciparum malaria in southern Cambodia. Malar J. 2009;8:10. https://doi.org/10.1186/1475-­2875-­8-­10. 22. van der Pluijm RW, Imwong M, Chau NH, Hoa NT, Thuy-Nhien NT, Thanh NV, et  al. Determinants of dihydroartemisinin-piperaquine treatment failure in Plasmodium falciparum malaria in Cambodia, Thailand, and Vietnam: a prospective clinical, pharmacological, and genetic study. Lancet Infect Dis. 2019;19(9):952–61. https://doi.org/10.1016/ S1473-­3099(19)30391-­3. 23. Korsinczky M, Chen N, Kotecka B, Saul A, Rieckmann K, Cheng Q.  Mutations in Plasmodium falciparum cytochrome b that are associated with atovaquone resistance are located at a putative drug-binding site. Antimicrob Agents Chemother. 2000;44(8):2100–8. https://doi.org/10.1128/AAC.44.8.2100-­2108.2000.

64

C. A. Patel et al.

24. Whitby M, Wood G, Veenendaal JR, Rieckmann K.  Chloroquine-resistant Plasmodium vivax, vol. 2. Lancet (London, England). England; 1989. p.  1395. https://doi.org/10.1016/ s0140-­6736(89)92002-­3. 25. Maguire JD, Sumawinata IW, Masbar S, Laksana B, Prodjodipuro P, Susanti I, et  al. Chloroquine-resistant Plasmodium malariae in south Sumatra, Indonesia. Lancet (London, UK). 2002;360(9326):58–60. https://doi.org/10.1016/S0140-­6736(02)09336-­4. 26. Hupalo DN, Luo Z, Melnikov A, Sutton PL, Rogov P, Escalante A, et al. Population genomics studies identify signatures of global dispersal and drug resistance in Plasmodium vivax. Nat Genet. 2016;48(8):953–8. Available from:. https://doi.org/10.1038/ng.3588. 27. Showler AJ, Kain KC, Boggild AK. Protozoan diseases: Malaria clinical features, management, and prevention, International Encyclopedia of Public Health, vol. 5. 2nd ed. Elsevier; 2016. 103–113 p. Available from:. https://doi.org/10.1016/B978-­0-­12-­803678-­5.00360-­X. 28. Reyburn H.  New WHO guidelines for the treatment of malaria. Vol. 340, BMJ (Clinical research ed.). England; 2010. p. c2637. https://doi.org/10.1136/bmj.c2637 29. Paget-McNicol S, Saul A.  Mutation rates in the dihydrofolate reductase gene of Plasmodium falciparum. Parasitology. 2001;122(Pt 5):497–505. https://doi.org/10.1017/ s0031182001007739. 30. Guyant P, Corbel V, Guérin PJ, Lautissier A, Nosten F, Boyer S, et al. Past and new challenges for malaria control and elimination: the role of operational research for innovation in designing interventions. Malar J. 2015;14(1):279. Available from:. https://doi.org/10.1186/ s12936-­015-­0802-­4. 31. Newton PN, Green MD, Mildenhall DC, Plançon A, Nettey H, Nyadong L, et  al. Poor quality vital anti-malarials in Africa  – an urgent neglected public health priority. Malar J. 2011;10(1):352. Available from:. https://doi.org/10.1186/1475-­2875-­10-­352. 32. Roux AT, Maharaj L, Oyegoke O, Akoniyon OP, Adeleke MA, Maharaj R, et al. Chloroquine and Sulfadoxine-Pyrimethamine resistance in Sub-Saharan Africa—a review. Front Genet. 2021;12:668574. https://doi.org/10.3389/fgene.2021.668574. 33. Homewood CA, Warhurst DC, Peters W, Baggaley VC. Lysosomes, pH and the anti-malarial action of chloroquine. Nature. 1972;235(5332):50–2. https://doi.org/10.1038/235050a0. 34. Yayon A, Cabantchik ZI, Ginsburg H. Identification of the acidic compartment of Plasmodium falciparum-infected human erythrocytes as the target of the antimalarial drug chloroquine. EMBO J. 1984;3(11):2695–700. 35. Chinappi M, Via A, Marcatili P, Tramontano A. On the mechanism of chloroquine resistance in Plasmodium falciparum. PLoS One. 2010;5(11):e14064. https://doi.org/10.1371/journal. pone.0014064. 36. Bossi R, Braga PC, Centanni S, Legnani D, Moavero NE, Allegra L.  Antitussive activity and respiratory system effects of levodropropizine in man. Arzneimittelforschung. 1988;38(8):1159–62. 37. Browning DJ.  Pharmacology of Chloroquine and Hydroxychloroquine. In: Hydroxychloroquine and Chloroquine Retinopathy. New  York: Springer; 2014. p.  35–63. https://doi.org/10.1007/978-­1-­4939-­0597-­3_2 38. Bray PG, Janneh O, Raynes KJ, Mungthin M, Ginsburg H, Ward SA.  Cellular uptake of chloroquine is dependent on binding to ferriprotoporphyrin IX and is independent of NHE activity in Plasmodium falciparum. J Cell Biol. 1999;145(2):363–76. https://doi.org/10.1083/ jcb.145.2.363. 39. Bray PG, Mungthin M, Ridley RG, Ward SA. Access to Hematin: the basis of chloroquine resistance. Mol Pharmacol. 1998;54(1):170–9. Available from: https://molpharm.aspetjournals.org/content/54/1/170 40. Ecker A, Lehane AM, Clain J, Fidock DA. PfCRT and its role in antimalarial drug resistance. Trends Parasitol. 2012;28(11):504–14. https://doi.org/10.1016/j.pt.2012.08.002. 41. Bray PG, Martin RE, Tilley L, Ward SA, Kirk K, Fidock DA. Defining the role of PfCRT in Plasmodium falciparum chloroquine resistance. Mol Microbiol. 2005;56(2):323–33. https:// doi.org/10.1111/j.1365-­2958.2005.04556.x.

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

65

42. Wellems TE, Plowe CV.  Chloroquine-resistant malaria. J Infect Dis. 2001;184(6):770–6. https://doi.org/10.1086/322858. 43. Martin RE, Kirk K. The malaria parasite’s chloroquine resistance transporter is a member of the drug/metabolite transporter superfamily. Mol Biol Evol. 2004;21(10):1938–49. https:// doi.org/10.1093/molbev/msh205. 44. Cooper RA, Lane KD, Deng B, Mu J, Patel JJ, Wellems TE, et al. Mutations in transmembrane domains 1, 4 and 9 of the Plasmodium falciparum chloroquine resistance transporter alter susceptibility to chloroquine, quinine and quinidine. Mol Microbiol. 2007;63(1):270–82. https://doi.org/10.1111/j.1365-­2958.2006.05511.x. 45. Doucette PA, Whitson LJ, Cao X, Schirf V, Demeler B, Valentine JS, et al. Dissociation of human copper-zinc superoxide dismutase dimers using chaotrope and reductant. Insights into the molecular basis for dimer stability. J Biol Chem. 2004;279(52):54558–66. https://doi. org/10.1074/jbc.M409744200. 46. Cooper RA, Hartwig CL, Ferdig MT. pfcrt is more than the Plasmodium falciparum chloroquine resistance gene: a functional and evolutionary perspective. Acta Trop. 2005;94(3):170–80. https://doi.org/10.1016/j.actatropica.2005.04.004. 47. Fidock DA, Nomura T, Talley AK, Cooper RA, Dzekunov SM, Ferdig MT, et al. Mutations in the P. falciparum digestive vacuole transmembrane protein PfCRT and evidence for their role in chloroquine resistance. Mol Cell. 2000;6(4):861–71. https://doi.org/10.1016/ s1097-­2765(05)00077-­8. 48. Cooper RA, Ferdig MT, Su X-Z, Ursos LMB, Mu J, Nomura T, et al. Alternative mutations at position 76 of the vacuolar transmembrane protein PfCRT are associated with chloroquine resistance and unique stereospecific quinine and quinidine responses in Plasmodium falciparum. Mol Pharmacol. 2002;61(1):35–42. https://doi.org/10.1124/mol.61.1.35. 49. Lehane AM, Kirk K.  Chloroquine resistance-conferring mutations in pfcrt give rise to a chloroquine-­associated H+ leak from the malaria parasite’s digestive vacuole. Antimicrob Agents Chemother. 2008;52(12):4374–80. https://doi.org/10.1128/AAC.00666-­08. 50. Beshir K, Sutherland CJ, Merinopoulos I, Durrani N, Leslie T, Rowland M, et al. Amodiaquine resistance in Plasmodium falciparum Malaria in Afghanistan is associated with the pfcrt SVMNT Allele at Codons 72 to 76. Antimicrob Agents Chemother. 2010;54(9):3714–6. https://doi.org/10.1128/AAC.00358-­10. 51. Ndung’u L, Langat B, Magiri E, Ng’ang’a J, Irungu B, Nzila A, et al. Amodiaquine resistance in Plasmodium berghei is associated with PbCRT His95Pro mutation, loss of chloroquine, artemisinin and primaquine sensitivity, and high transcript levels of key transporters. Wellcome Open Res. 2017;2:44. https://doi.org/10.12688/wellcomeopenres.11768.2. 52. Price RN, Uhlemann A-C, Brockman A, McGready R, Ashley E, Phaipun L, et al. Mefloquine resistance in Plasmodium falciparum and increased pfmdr1 gene copy number. Lancet (London, UK). 2004;364(9432):438–47. https://doi.org/10.1016/S0140-­6736(04)16767-­6. 53. Preechapornkul P, Imwong M, Chotivanich K, Pongtavornpinyo W, Dondorp AM, Day NPJ, et al. Plasmodium falciparum pfmdr1 amplification, mefloquine resistance, and parasite fitness. Antimicrob Agents Chemother. 2009;53(4):1509–15. https://doi.org/10.1128/ AAC.00241-­08. 54. Baliraine FN, Rosenthal PJ.  Prolonged selection of pfmdr1 polymorphisms after treatment of falciparum malaria with artemether-lumefantrine in Uganda. J Infect Dis. 2011;204(7):1120–4. https://doi.org/10.1093/infdis/jir486. 55. Windle ST, Lane KD, Gadalla NB, Liu A, Mu J, Caleon RL, et al. Evidence for linkage of pfmdr1, pfcrt, and pfk13 polymorphisms to lumefantrine and mefloquine susceptibilities in a Plasmodium falciparum cross. Int J Parasitol Drugs Drug Resist. 2020;14:208–17. Available from: https://www.sciencedirect.com/science/article/pii/S2211320720300403 56. Pickard AL, Wongsrichanalai C, Purfield A, Kamwendo D, Emery K, Zalewski C, et  al. Resistance to antimalarials in Southeast Asia and genetic polymorphisms in pfmdr1. Antimicrob Agents Chemother. 2003;47(8):2418–23. https://doi.org/10.1128/ AAC.47.8.2418-­2423.2003.

66

C. A. Patel et al.

57. Mu J, Ferdig MT, Feng X, Joy DA, Duan J, Furuya T, et  al. Multiple transporters associated with malaria parasite responses to chloroquine and quinine. Mol Microbiol. 2003;49(4):977–89. https://doi.org/10.1046/j.1365-­2958.2003.03627.x. 58. Gregson A, Plowe CV.  Mechanisms of resistance of malaria parasites to Antifolates. Pharmacol Rev. 2005;57(1):117–45. Available from: https://pharmrev.aspetjournals.org/ content/57/1/117 59. Yuthavong Y.  Basis for antifolate action and resistance in malaria. Microbes Infect. 2002;4(2):175–82. https://doi.org/10.1016/s1286-­4579(01)01525-­8. 60. Nzila A.  The past, present and future of antifolates in the treatment of Plasmodium falciparum infection. J Antimicrob Chemother. 2006;57(6):1043–54. Available from:. https://doi. org/10.1093/jac/dkl104. 61. Sridaran S, McClintock SK, Syphard LM, Herman KM, Barnwell JW, Udhayakumar V. Anti-­ folate drug resistance in Africa: meta-analysis of reported dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) mutant genotype frequencies in African Plasmodium falciparum parasite populations. Malar J. 2010;9(1):247. Available from:. https://doi.org/10.118 6/1475-­2875-­9-­247. 62. Japrung D, Leartsakulpanich U, Chusacultanachai S, Yuthavong Y. Conflicting requirements of Plasmodium falciparum dihydrofolate reductase mutations conferring resistance to pyrimethamine-­WR99210 combination. Antimicrob Agents Chemother. 2007;51(12):4356–60. https://doi.org/10.1128/AAC.00577-­07. 63. Jiang T, Chen J, Fu H, Wu K, Yao Y, Eyi JUM, et al. High prevalence of Pfdhfr–Pfdhps quadruple mutations associated with sulfadoxine–pyrimethamine resistance in Plasmodium falciparum isolates from Bioko Island, Equatorial Guinea. Malar J. 2019;18(1):101. Available from:. https://doi.org/10.1186/s12936-­019-­2734-­x. 64. Reed MB, Saliba KJ, Caruana SR, Kirk K, Cowman AF. Pgh1 modulates sensitivity and resistance to multiple antimalarials in Plasmodium falciparum. Nature. 2000;403(6772):906–9. https://doi.org/10.1038/35002615. 65. Corrêa Soares JBR, Menezes D, Vannier-Santos MA, Ferreira-Pereira A, Almeida GT, Venancio TM, et  al. Interference with hemozoin formation represents an important ­mechanism of schistosomicidal action of antimalarial quinoline methanols. PLoS Negl Trop Dis. 2009;3(7):e477. https://doi.org/10.1371/journal.pntd.0000477. 66. Eastman RT, Fidock DA.  Artemisinin-based combination therapies: a vital tool in efforts to eliminate malaria. Nat Rev Microbiol. 2009;7(12):864–74. https://doi.org/10.1038/ nrmicro2239. 67. Bray PG, Ward SA, O’Neill PM. Quinolines and artemisinin: chemistry, biology and history. Curr Top Microbiol Immunol. 2005;295:3–38. https://doi.org/10.1007/3-­540-­29088-­5_1. 68. Jambou R, Legrand E, Niang M, Khim N, Lim P, Volney B, et al. Resistance of Plasmodium falciparum field isolates to in-vitro artemether and point mutations of the SERCA-type PfATPase6. Lancet (London, UK). 2005;366(9501):1960–3. https://doi.org/10.1016/ S0140-­6736(05)67787-­2. 69. Hunt P, Afonso A, Creasey A, Culleton R, Sidhu ABS, Logan J, et al. Gene encoding a deubiquitinating enzyme is mutated in artesunate- and chloroquine-resistant rodent malaria parasites. Mol Microbiol. 2007;65(1):27–40. https://doi.org/10.1111/j.1365-­2958.2007.05753.x. 70. Ariey F, Witkowski B, Amaratunga C, Beghain J, Langlois A-C, Khim N, et  al. A molecular marker of artemisinin-resistant Plasmodium falciparum malaria. Nature. 2014;505(7481):50–5. https://doi.org/10.1038/nature12876. 71. Yeh E, DeRisi JL. Chemical rescue of malaria parasites lacking an apicoplast defines organelle function in blood-stage Plasmodium falciparum. PLoS Biol. 2011;9(8):e1001138. https:// doi.org/10.1371/journal.pbio.1001138. 72. Lell B, Kremsner PG.  Clindamycin as an antimalarial drug: review of clinical trials. Antimicrob Agents Chemother. 2002;46(8):2315–20. https://doi.org/10.1128/ AAC.46.8.2315-­2320.2002.

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

67

73. Obonyo CO, Juma EA.  Clindamycin plus quinine for treating uncomplicated falciparum malaria: a systematic review and meta-analysis. Malar J. 2012;11:2. https://doi.org/10.118 6/1475-­2875-­11-­2. 74. Ramharter M, Oyakhirome S, Klein Klouwenberg P, Adégnika AA, Agnandji ST, Missinou MA, et  al. Artesunate-clindamycin versus quinine-clindamycin in the treatment of Plasmodium falciparum malaria: a randomized controlled trial. Clin Infect Dis an Off Publ Infect Dis Soc Am. 2005;40(12):1777–84. https://doi.org/10.1086/430309. 75. Hodoameda P. P. falciparum and its molecular markers of resistance to antimalarial drugs. In: Tyagi RK, editor. Plasmodium species and drug resistance. Rijeka: IntechOpen; 2021. Available from:. https://doi.org/10.5772/intechopen.98372. 76. Djimdé A, Doumbo OK, Cortese JF, Kayentao K, Doumbo S, Diourté Y, et al. A molecular marker for chloroquine-resistant falciparum malaria. N Engl J Med. 2001;344(4):257–63. https://doi.org/10.1056/NEJM200101253440403. 77. Menard D, Yapou F, Manirakiza A, Djalle D, Matsika-Claquin MD, Talarmin A.  Polymorphisms in pfcrt, pfmdr1, dhfr genes and in  vitro responses to antimalarials in Plasmodium falciparum isolates from Bangui, Central African Republic. Am J Trop Med Hyg. 2006;75(3):381–7. 78. Echeverry DF, Holmgren G, Murillo C, Higuita JC, Björkman A, Gil JP, et al. Short report: polymorphisms in the pfcrt and pfmdr1 genes of Plasmodium falciparum and in vitro susceptibility to amodiaquine and desethylamodiaquine. Am J Trop Med Hyg. 2007;77(6):1034–8. 79. Ferreira PE, Holmgren G, Veiga MI, Uhlén P, Kaneko A, Gil JP. PfMDR1: mechanisms of transport modulation by functional polymorphisms. PLoS One. 2011;6(9):e23875. https:// doi.org/10.1371/journal.pone.0023875. 80. Wilson CM, Volkman SK, Thaithong S, Martin RK, Kyle DE, Milhous WK, et  al. Amplification of pfmdr 1 associated with mefloquine and halofantrine resistance in Plasmodium falciparum from Thailand. Mol Biochem Parasitol. 1993;57(1):151–60. https:// doi.org/10.1016/0166-­6851(93)90252-­s. 81. Picot S, Olliaro P, de Monbrison F, Bienvenu A-L, Price RN, Ringwald P.  A systematic review and meta-analysis of evidence for correlation between molecular markers of ­parasite resistance and treatment outcome in falciparum malaria. Malar J. 2009;8:89. https://doi.org/1 0.1186/1475-­2875-­8-­89. 82. Dokomajilar C, Nsobya SL, Greenhouse B, Rosenthal PJ, Dorsey G. Selection of Plasmodium falciparum pfmdr1 alleles following therapy with artemether-lumefantrine in an area of Uganda where malaria is highly endemic. Antimicrob Agents Chemother. 2006;50(5):1893–5. https://doi.org/10.1128/AAC.50.5.1893-­1895.2006. 83. Sisowath C, Petersen I, Veiga MI, Mårtensson A, Premji Z, Björkman A, et al. In vivo selection of Plasmodium falciparum parasites carrying the chloroquine-susceptible pfcrt K76 allele after treatment with artemether-lumefantrine in Africa. J Infect Dis. 2009;199(5):750–7. https://doi.org/10.1086/596738. 84. Anderson TJC, Nair S, Qin H, Singlam S, Brockman A, Paiphun L, et al. Are transporter genes other than the chloroquine resistance locus (pfcrt) and multidrug resistance gene (pfmdr) associated with antimalarial drug resistance? Antimicrob Agents Chemother. 2005;49(6):2180–8. https://doi.org/10.1128/AAC.49.6.2180-­2188.2005. 85. Raj DK, Mu J, Jiang H, Kabat J, Singh S, Sullivan M, et al. Disruption of a Plasmodium falciparum multidrug resistance-associated protein (PfMRP) alters its fitness and transport of antimalarial drugs and glutathione. J Biol Chem. 2009;284(12):7687–96. https://doi. org/10.1074/jbc.M806944200. 86. Bosia A, Ghigo D, Turrini F, Nissani E, Pescarmona GP, Ginsburg H.  Kinetic characterization of Na+/H+ antiport of Plasmodium falciparum membrane. J Cell Physiol. 1993;154(3):527–34. https://doi.org/10.1002/jcp.1041540311. 87. Ferdig MT, Cooper RA, Mu J, Deng B, Joy DA, Su X, et  al. Dissecting the loci of low-­ level quinine resistance in malaria parasites. Mol Microbiol. 2004;52(4):985–97. https://doi. org/10.1111/j.1365-­2958.2004.04035.x.

68

C. A. Patel et al.

88. Hyde JE.  Exploring the folate pathway in Plasmodium falciparum. Acta Trop. 2005;94(3):191–206. https://doi.org/10.1016/j.actatropica.2005.04.002. 89. Cowman AF, Morry MJ, Biggs BA, Cross GA, Foote SJ.  Amino acid changes linked to pyrimethamine resistance in the dihydrofolate reductase-thymidylate synthase gene of Plasmodium falciparum. Proc Natl Acad Sci USA. 1988;85(23):9109–13. https://doi. org/10.1073/pnas.85.23.9109. 90. Thaithong S, Ranford-Cartwright LC, Siripoon N, Harnyuttanakorn P, Kanchanakhan NS, Seugorn A, et al. Plasmodium falciparum: gene mutations and amplification of dihydrofolate reductase genes in parasites grown in  vitro in presence of pyrimethamine. Exp Parasitol. 2001;98(2):59–70. https://doi.org/10.1006/expr.2001.4618. 91. Urdaneta L, Plowe C, Goldman I, Lal AA. Point mutations in dihydrofolate reductase and dihydropteroate synthase genes of Plasmodium falciparum isolates from Venezuela. Am J Trop Med Hyg. 1999;61(3):457–62. https://doi.org/10.4269/ajtmh.1999.61.457. 92. Wernsdorfer WH, Noedl H. Molecular markers for drug resistance in malaria: use in treatment, diagnosis and epidemiology. Curr Opin Infect Dis. 2003;16(6):553–8. https://doi. org/10.1097/00001432-­200312000-­00007. 93. Krishna S, Pulcini S, Fatih F, Staines H. Artemisinins and the biological basis for the PfATP6/ SERCA hypothesis. Trends Parasitol. 2010;26(11):517–23. https://doi.org/10.1016/j. pt.2010.06.014. 94. Ashley EA, Dhorda M, Fairhurst RM, Amaratunga C, Lim P, Suon S, et al. Spread of artemisinin resistance in Plasmodium falciparum malaria. N Engl J Med. 2014;371(5):411–23. https://doi.org/10.1056/NEJMoa1314981. 95. Barton V, Fisher N, Biagini GA, Ward SA, O’Neill PM. Inhibiting Plasmodium cytochrome bc1: a complex issue. Curr Opin Chem Biol. 2010;14(4):440–6. https://doi.org/10.1016/j. cbpa.2010.05.005. 96. Hawkins VN, Joshi H, Rungsihirunrat K, Na-Bangchang K, Sibley CH. Antifolates can have a role in the treatment of Plasmodium vivax. Trends Parasitol. 2007;23(5):213–22. https:// doi.org/10.1016/j.pt.2007.03.002. 97. Lu F, Culleton R, Zhang M, Ramaprasad A, von Seidlein L, Zhou H, et al. Emergence of indigenous artemisinin-resistant Plasmodium falciparum in Africa. New England J Med USA. 2017;376:991–3. https://doi.org/10.1056/NEJMc1612765. 98. Devine SM, MacRaild CA, Norton RS, Scammells PJ. Antimalarial drug discovery targeting apical membrane antigen 1. MedChemComm. 2017;8(1):13–20. https://doi.org/10.1039/ c6md00495d. 99. Cowell AN, Istvan ES, Lukens AK, Gomez-Lorenzo MG, Vanaerschot M, Sakata-Kato T, et al. Mapping the malaria parasite druggable genome by using in vitro evolution and chemogenomics. Science. 2018;359(6372):191–9. https://doi.org/10.1126/science.aan4472. 100. Renslo AR. Antimalarial drug discovery: from Quinine to the Dream of Eradication. ACS Med Chem Lett. 2013;4(12):1126–8. https://doi.org/10.1021/ml4004414. 101. Davis TME, Karunajeewa HA, Ilett KF. Artemisinin-based combination therapies for uncomplicated malaria. Med J Aust. 2005;182(4):181–5. https://doi.org/10.5694/j.1326-­5377.2005. tb06650.x. 102. Kimani J, Phiri K, Kamiza S, Duparc S, Ayoub A, Rojo R, et  al. Efficacy and safety of Azithromycin-Chloroquine versus Sulfadoxine-Pyrimethamine for intermittent preventive treatment of Plasmodium falciparum malaria infection in pregnant women in Africa: an open-label, randomized trial. PLoS One. 2016;11(6):e0157045. https://doi.org/10.1371/ journal.pone.0157045. 103. Coulibaly B, Pritsch M, Bountogo M, Meissner PE, Nebié E, Klose C, et al. Efficacy and safety of triple combination therapy with artesunate-amodiaquine-methylene blue for falciparum malaria in children: a randomized controlled trial in Burkina Faso. J Infect Dis. 2015;211(5):689–97. https://doi.org/10.1093/infdis/jiu540. 104. Rosenthal PJ. Antimalarial drug discovery: old and new approaches. J Exp Biol. 2003;206(Pt 21):3735–44. https://doi.org/10.1242/jeb.00589.

Antimalarial Drug Resistance: Trends, Mechanisms, and Strategies to Combat…

69

105. Sidhu ABS, Verdier-Pinard D, Fidock DA. Chloroquine resistance in Plasmodium falciparum malaria parasites conferred by pfcrt mutations. Science. 2002;298(5591):210–3. https://doi. org/10.1126/science.1074045. 106. Kublin JG, Cortese JF, Njunju EM, Mukadam RAG, Wirima JJ, Kazembe PN, et  al. Reemergence of chloroquine-sensitive Plasmodium falciparum malaria after cessation of chloroquine use in Malawi. J Infect Dis. 2003;187(12):1870–5. https://doi.org/10.1086/375419. 107. Mohammed A, Ndaro A, Kalinga A, Manjurano A, Mosha JF, Mosha DF, et al. Trends in chloroquine resistance marker, Pfcrt-K76T mutation ten years after chloroquine withdrawal in Tanzania. Malar J. 2013;12:415. https://doi.org/10.1186/1475-­2875-­12-­415. 108. Drinkwater N, McGowan S.  From crystal to compound: structure-based antimalarial drug discovery. Biochem J. 2014;461(3):349–69. https://doi.org/10.1042/BJ20140240. 109. Comer E, Beaudoin JA, Kato N, et  al. Diversity-oriented synthesis-facilitated medicinal chemistry: toward the development of novel antimalarial agents. J Med Chem. 2014;57(20):8496–502. https://doi.org/10.1021/jm500994n. 110. Deu E.  Proteases as antimalarial targets: strategies for genetic, chemical, and therapeutic validation. FEBS J. 2017;284(16):2604–28. https://doi.org/10.1111/febs.14130. 111. McNamara CW, Lee MC, Lim CS, Lim SH, Roland J, Simon O, et al. Targeting Plasmodium PI(4)K to eliminate malaria. Nature. 2013;504(7479):248–53. https://doi.org/10.1038/ nature12782. 112. Rottmann M, McNamara C, Yeung BKS, Lee MCS, Zou B, Russell B, et al. Spiroindolones, a potent compound class for the treatment of malaria. Science. 2010;329(5996):1175–80. https://doi.org/10.1126/science.1193225. 113. Baragaña B, Hallyburton I, Lee MCS, Norcross NR, Grimaldi R, Otto TD, et  al. A novel multiple-­ stage antimalarial agent that inhibits protein synthesis. Nature. 2015;522(7556):315–20. https://doi.org/10.1038/nature14451. 114. Phillips MA, Lotharius J, Marsh K, White J, Dayan A, White KL, et  al. A long-duration dihydroorotate dehydrogenase inhibitor (DSM265) for prevention and treatment of malaria. Sci Transl Med. 2015;7(296):296ra111. https://doi.org/10.1126/scitranslmed.aaa6645. 115. Coelho CH, Doritchamou JYA, Zaidi I, Duffy PE.  Advances in malaria vaccine development: report from the 2017 malaria vaccine symposium. NPJ Vaccin. 2017;2:34. https://doi. org/10.1038/s41541-­017-­0035-­3. 116. Han L, Hudgens MG, Emch ME, Juliano JJ, Keeler C, Martinson F, et  al. RTS,S/AS01 malaria vaccine efficacy is not modified by seasonal precipitation: results from a phase 3 randomized controlled trial in Malawi. Sci Rep. 2017;7(1):7200. https://doi.org/10.1038/ s41598-­017-­07533-­w.

Malaria – Current Treatment Options Dita Maria Virginia, Ranjita Shegokar, and Yashwant Pathak

Abstract  Malaria diseases are caused by Plasmodium, either P. falciparum or non-­ P. falciparum requires antimalarial treatment guidelines. Artemisinin-based combination (ACT) therapies are recommended as first-line therapy for uncomplicated P. falciparum and second-line therapy for non-P. falciparum. There are five ACTs approved by WHO: artesunate-amodiaquine, artemether-lumefantrine (AL), artesunate-­ mefloquine, artesunate-sulfadoxine-pyrimethamine, and dihydroartemisinin-­piperaquine (DHA  +  PPQ). Quinine derivates are considered the first-line choice for non-P. falciparum infection. Intravenous artesunate is the first-line therapy for severe P. falciparum. Amodiaquine + sulfadoxine-­ pyrimethamine (SP) monthly is recommended for all children aged 2% and/or pregnant women), present vomiting, and are unable to consume oral antimalaria (the UK). Artesunate as intravenous should be the first choice of severe P. falciparum therapy [10]. Artesunate is not approved in the European Union (2015), but it is licensed in WHO prequalification standards. Several specialists of tropical disease in the UK remain to prescribe artesunate as intravenous. Patients who were diagnosed with severe P. falciparum could not delay the therapy while awaiting artesunate. Therefore, they should receive quinine immediately if artesunate is not available (Grade 1A). In fact, there is no benefit in combining artesunate and quinine, but it is considered safe. Patients receiving intravenous artesunate minimum of 24  h, improving their conditions, and can take oral medications should consume a full course of ACT (artemether-lumefantrine or DHA-PPQ). A full course of quinine and doxycycline is an alternative, but clindamycin is the choice for children/pregnant women. [3, 11]

1.3 Non-P. falciparum Malaria Patients who could not be detected malaria species certainly should be treated according to non-P. falciparum malaria therapy algorithm. In fact, P. ovale, P. malariae, and P. vivax are not life-threatening unless patients have other comorbidities or are intolerant to oral medication. Therefore, patients could get outpatient management [3]. However, the clinician should give more attention to the rare presentation case caused by P. vivax and P. ovale, which could modulate severe conditions in particular circumstances. A review of 77 studies on P. vivax, which were mainly observed in India, the USA, Indonesia, and Pakistan, reported that P. vivax induces severe thrombocytopenia (