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Fats & Fakes Towards improved control of malaria Visser, B.J.

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Citation for published version (APA): Visser, B. J. (2017). Fats & Fakes: Towards improved control of malaria.

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Download date:28 Sep 2021 Chapter 2

Discovery of the Malaria Parasites and their Vectors – A Short History

Benjamin J. Visser Martin P. Grobusch

Discoveries in Modern Science: Exploration, Invention, Technology, 1st ed. 2015, Chapter: Malaria Is Transmitted by Mosquitoes, Publisher: Macmillan Reference USA, Editors: James Trefil, Patricia Daniels, Donna McPhie, Craig Schiffries, pp.640-647

“Land cover map of Africa. This map was produced for the year 2000 using data collected by sensors on satellites.” Adapted from: Soil Atlas of Africa, 2013. European Commission, Publications Office of the European Union, Luxembourg.1

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Discovery of the Malaria Parasites and their Vectors – A Short History

Benjamin J. Visser Martin P. Grobusch

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Abstract Introduction

Malaria is an ancient disease continuing to pose an enormous health, social, and economic Malaria is an ancient disease causing an enormous health, social, and economic burden51, 52. burden. It is caused by infection with protozoan parasites belonging to the genus It has been described for more than four millennia and is understood to have changed human Plasmodium transmitted via the bite of female Anopheles species mosquitoes. Of more than populations and the course of human history53, 54. Malaria continues to sicken hundreds of 100 different species infecting a wide range of animals from rodents and birds to mammals, millions of people, resulting in an estimated number of preventable deaths exceeding one five species of malaria parasites are known to infect humans: Plasmodium falciparum, P. million per year (1.2 million in 2010), most of them children under five years of age in sub- vivax, P. ovale (now being recognized as consisting of two subspecies), P. malariae and P. Saharan Africa3. In many aspects, the multifaceted history of malaria illuminates the knowlesi. P. falciparum is most likely to cause severe disease and, if not promptly treated, evolution of modern science and medicine over the centuries, from myths and supernatural may lead to death. References to the disease occur in the Chinese canon of medicine, clay beliefs to evidence-based scientific insights55. Poverty and inequality, as much as geography tablets from Mesopotamia, Egyptian papyri and Indian medical works. Descriptions of and climate, made malaria only recently a ‘‘tropical’’ disease: even in the early twentieth malaria from classic Greece and the Roman Empire are abundant. It was commonly believed century it afflicted temperate regions of North America stretching northward into Canada, that malaria was caused by marsh water and foul vapors emanating from swamps, hence the western and northern Europe, and Central and East Asia (see Figure 1)56, 57. Elimination of word mal’aria, from the Italian for “bad air”. For thousands of years, no effective treatment the disease was achieved progressively from many of these areas, and following these was available. This changed with the discovery of Artemisia annua (sweet wormwood) in successes, the World Health Organization (WHO) Global Malaria Eradication Program was China and the use of quinine from Peruvian bark as potent and effective drugs against launched in the late 1950s. There were many accomplishments; however, in the heartlands malaria. The current understanding of the malaria parasites and their lifecycle starts in the of malaria (especially sub-Saharan Africa) the disease remains a dangerous and resilient end of the nineteenth century with the discovery of the malaria parasites in the blood of foe58. Climate change is predicted to have unexpected consequences on malaria distribution malaria patients by Alphonse Laveran in 1880. Subsequently, Ronald Ross discovered in and incidence59. Changes in rainfall, and rising as well as fluctuating temperatures, influence 1897 that a bird malaria parasite was transmitted by mosquitoes. In 1898 Giovanni Grassi, the Anopheles mosquito vectors60. In addition, the malaria life cycle can be altered by Camillo Golgi, Ettore Marchiafava, Amico Bignami, Angelo Celli and Giuseppe Bastianelli temperature variations that influence parasite development within the mosquito (the extrinsic confirmed that malaria in humans was also a mosquito-borne disease, in this case Anopheles incubation development)61. Climate change, which may lead to altitudinal and latitudinal species. Grassi and Filetti introduced the names of P. vivax and P. malariae in 1890. The temperature increases, pose a particular risk for high-elevation areas and regions with a causative agent of what was dubbed ‘malignant malaria’ was baptized P. falciparum by temperate climate59, 62. Climate change can result in reduced prevalence in some areas, while William Welch in 1897 and P. ovale by John Stephens in 1922. The discovery of a liver it may increase or be (re-)introduced in others60, 63. stage before malaria enters the bloodstream was made by Henry Shortt and Cyril Garnham in 1948. The existence of dormant stages, in P. vivax and P. ovale was shown in 1982 by Wojciech Krotoski. This chapter describes the key discoveries and provides a short overview of the multifaceted history of malaria.

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Abstract Introduction

Malaria is an ancient disease continuing to pose an enormous health, social, and economic Malaria is an ancient disease causing an enormous health, social, and economic burden51, 52. burden. It is caused by infection with protozoan parasites belonging to the genus It has been described for more than four millennia and is understood to have changed human Plasmodium transmitted via the bite of female Anopheles species mosquitoes. Of more than populations and the course of human history53, 54. Malaria continues to sicken hundreds of 100 different species infecting a wide range of animals from rodents and birds to mammals, millions of people, resulting in an estimated number of preventable deaths exceeding one 2 five species of malaria parasites are known to infect humans: Plasmodium falciparum, P. million per year (1.2 million in 2010), most of them children under five years of age in sub- vivax, P. ovale (now being recognized as consisting of two subspecies), P. malariae and P. Saharan Africa3. In many aspects, the multifaceted history of malaria illuminates the knowlesi. P. falciparum is most likely to cause severe disease and, if not promptly treated, evolution of modern science and medicine over the centuries, from myths and supernatural may lead to death. References to the disease occur in the Chinese canon of medicine, clay beliefs to evidence-based scientific insights55. Poverty and inequality, as much as geography tablets from Mesopotamia, Egyptian papyri and Indian medical works. Descriptions of and climate, made malaria only recently a ‘‘tropical’’ disease: even in the early twentieth malaria from classic Greece and the Roman Empire are abundant. It was commonly believed century it afflicted temperate regions of North America stretching northward into Canada, that malaria was caused by marsh water and foul vapors emanating from swamps, hence the western and northern Europe, and Central and East Asia (see Figure 1)56, 57. Elimination of word mal’aria, from the Italian for “bad air”. For thousands of years, no effective treatment the disease was achieved progressively from many of these areas, and following these was available. This changed with the discovery of Artemisia annua (sweet wormwood) in successes, the World Health Organization (WHO) Global Malaria Eradication Program was China and the use of quinine from Peruvian bark as potent and effective drugs against launched in the late 1950s. There were many accomplishments; however, in the heartlands malaria. The current understanding of the malaria parasites and their lifecycle starts in the of malaria (especially sub-Saharan Africa) the disease remains a dangerous and resilient end of the nineteenth century with the discovery of the malaria parasites in the blood of foe58. Climate change is predicted to have unexpected consequences on malaria distribution malaria patients by Alphonse Laveran in 1880. Subsequently, Ronald Ross discovered in and incidence59. Changes in rainfall, and rising as well as fluctuating temperatures, influence 1897 that a bird malaria parasite was transmitted by mosquitoes. In 1898 Giovanni Grassi, the Anopheles mosquito vectors60. In addition, the malaria life cycle can be altered by Camillo Golgi, Ettore Marchiafava, Amico Bignami, Angelo Celli and Giuseppe Bastianelli temperature variations that influence parasite development within the mosquito (the extrinsic confirmed that malaria in humans was also a mosquito-borne disease, in this case Anopheles incubation development)61. Climate change, which may lead to altitudinal and latitudinal species. Grassi and Filetti introduced the names of P. vivax and P. malariae in 1890. The temperature increases, pose a particular risk for high-elevation areas and regions with a causative agent of what was dubbed ‘malignant malaria’ was baptized P. falciparum by temperate climate59, 62. Climate change can result in reduced prevalence in some areas, while William Welch in 1897 and P. ovale by John Stephens in 1922. The discovery of a liver it may increase or be (re-)introduced in others60, 63. stage before malaria enters the bloodstream was made by Henry Shortt and Cyril Garnham in 1948. The existence of dormant stages, in P. vivax and P. ovale was shown in 1982 by Wojciech Krotoski. This chapter describes the key discoveries and provides a short overview of the multifaceted history of malaria.

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early the Greeks inductively associated malaria with swamps68. Hippocrates, in about 400 B.C.E., noted the most important symptoms, described different stages of a malaria attack, and noticed the seasonal character of the disease and the noxious consequences of wet springs and dry summers. The same familiarity with malaria is shown in the writings of Plato, Aristotle, and later Greek authors68. When malaria was introduced into Italy is unclear, yet the evidence that Rome and major parts of the Roman Empire were highly malarious are overwhelming. Several authors, such as M. Porcius Cato, Cicero, Marcus Terentius Varro, and others, described malaria and warned residents of marshy places68. Both the Greeks and Romans became more certain that there were some causal relations between intermittent fevers and swampy terrain. This, among other things, resulted in the use of drains to mitigate the detrimental effect of stagnant water. It was suggested that marsh water and marsh vapours were causal factors, hence the name mal’aria, from the Italian for ‘‘bad air.’’

Malaria treatments

The rediscovery of artemisinin by Chinese scientists for malaria treatment was one of the greatest achievements in medicine in the twentieth century69. Archaeological findings th Figure 1. World distribution of malaria, Mid-19 century to 2010. Note: This composite map does suggest that Artemisia annua, also known as sweet wormwood, has been used in China for not claim to be complete. It is intended to illustrate where malaria transmission existed over the years. thousands of years to treat many illnesses, including malaria. During the second century Source: Adapted from: “Eliminating Malaria: Learning from the Past, Looking Ahead. “ P&I series B.C.E., the herbal remedy qinghaosu, obtained from the qinghao plant (Artemisia annua) report. Available at: http://www.rollbackmalaria.org/microsites/wmd2014/report9.html was described as anti-fever medicine in the Fifty-Two Remedies, a medical treatise discovered in the Mawangdui Tomb (Changsha, China) in 197270, 71. In 340 B.C.E., the Artemisia annua plant was first described in the Handbook of Prescriptions for Emergency Malaria in ancient history Treatments, by the alchemist Ge Hong of the East Yin Dynasty72. Yet for a long time this Malaria was known in China long before classical antiquity and the Christian era64. The ancient drug had fallen out of common use. In 1967 the top secret Project 523 was symptoms of malaria, or disease resembling malaria, was described in the Chinese medical established by the Chinese government during the Vietnam War, involving 500 scientists in classic Nei Ching (the Canon of Medicine) in 2700 B.C.E., edited by the legendary Yellow about 60 laboratories and research institutes, to develop new antimalarials to aid North- Emperor Huang Ti.65 It contains descriptions of different types of fevers and already Vietnamese troops73. During the war, malaria caused by chloroquine-resistant Plasmodium differentiated tertian (every third day) from quartan (every fourth day) fevers with falciparum was a major health problem that urged malaria research efforts on both sides. enlargements of the spleen. Clay tablets from Mesopotamia from 2000 B.C.E., and Egyptian Because the research was secret, publication in scientific journals was forbidden, and it is papyri from 1570 B.C.E. describe malaria66. In India, the symptoms of malarial fever were therefore hard to decide who exactly should be credited with the (re)discovery of artemisinin. described in the Charaka Samhita and the Susrata Samhita and other medical works67. In 1971 Chinese scientists led by Youyou Tu (1930– ), recognized its potential for treating Tertian and quartan fevers and a ‘‘splenic’’ belly were described and were considered as a malaria and isolated the active ingredient of qinghao, known as artemisinin73. Its rapid most dreaded affliction, attributed to the anger of the god Shiva. Five types of mosquitoes action, low toxicity, and potent effect against the most dangerous species, Plasmodium were described and blamed for the transmission of this ‘‘king of diseases’’68. These ancient falciparum malaria, made it a favored subject for research. Between 1976 and 1978 the historical records must be regarded with caution as less than firm and controversial compared molecular structure of artemisinin was discovered, and new artemisinin derivatives were to sources from classical antiquity. Literature from Greek sources is extensive; malaria was developed74. In 1979 artemisinin-based antimalarial drugs were successfully used in the widely endemic in Greece by the sixth century B.C.E., and it was responsible for the decline combat zone in the Sino-Vietnamese War (the Third Indo-China War). Derivates of this of many of the city-state populations. In about 550 B.C.E. the philosopher Empedocles of compound are today the most potent and effective antimalarial drugs. Artemisinin Agrigentum, who resolved a ‘‘plague’’ in Sicily by draining marshes, demonstrates how

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early the Greeks inductively associated malaria with swamps68. Hippocrates, in about 400 B.C.E., noted the most important symptoms, described different stages of a malaria attack, and noticed the seasonal character of the disease and the noxious consequences of wet springs and dry summers. The same familiarity with malaria is shown in the writings of Plato, Aristotle, and later Greek authors68. When malaria was introduced into Italy is unclear, yet the evidence that Rome and major parts of the Roman Empire were highly malarious are 2 overwhelming. Several authors, such as M. Porcius Cato, Cicero, Marcus Terentius Varro, and others, described malaria and warned residents of marshy places68. Both the Greeks and Romans became more certain that there were some causal relations between intermittent fevers and swampy terrain. This, among other things, resulted in the use of drains to mitigate the detrimental effect of stagnant water. It was suggested that marsh water and marsh vapours were causal factors, hence the name mal’aria, from the Italian for ‘‘bad air.’’

Malaria treatments

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combination therapies (ACTs) are recommended by the World Health Organization and are However, as for many antimicrobial drugs, eventually (two decades later) drug-resistant the first-line treatment in nearly all malaria-endemic countries. strains developed77. In the second half of the twentieth century, another important antimalarial drug was also developed in a time of war: mefloquine was number 142,490 of a total of 250,000 antimalarial compounds screened during the US Army’s antimalarial drug Quinine from the New World discovery program 79. It was discovered shortly after the Vietnam War in the 1970s, and subsequently marketed worldwide. The curative virtues of the Peruvian bark, also known as Jesuit’s bark, first became known to Europeans about 1630, following the arrival of Spanish Jesuit missionaries in the New 68, 75 ό World . The legendary story that the Countess of Chinch n, wife of the Viceroy of Peru, Discovery of the life cycle of the malaria parasite in humans was cured of her fever by using this bark, which she supposedly later brought to Spain, has been disputed68. It is more likely that this indigenous remedy was discovered by observing With the discovery of bacteria by the Dutch tradesman and scientist Antoni van practices of indigenous Indian herbalists by the Jesuits. Nevertheless, the tree was given the Leeuwenhoek (1632–1723) in the Netherlands in 1676—along with the subsequent generic name cinchona, after the Countess of Chinchόn. The acceptance of the cinchona discoveries of the French chemist and microbiologist Louis Pasteur (1822–1895) and the bark as antimalarial was arduous and slow, and doubts regarding its efficacy lingered for a German physician and microbiologist Robert Koch (1843–1910) in 1878–1879 that many long time68. Many physicians hesitated to use the bark because of the many attributed diseases are caused by microbes (known as the germ theory)—the search for a bacterial toxicities. Yet the rising demand for an effective antimalarial prompted botanical expeditions origin of malaria intensified80. Many studies subsequently searched unsuccessfully for an to the New World by the British and the Dutch76. This was hampered when in the nineteenth infectious agent in marshland soil. century South American countries began outlawing the export of cinchona seeds. After a successful attempt to smuggle the famous Cinchona ledgeriana strain from Bolivia, the South American monopoly was destroyed. Plantations were set up in the British Empire in Alphonse Laveran Discovers the Malaria Parasite India and Ceylon (Sri Lanka) and by the Dutch in Java, the Dutch East Indies, to produce large quantities of the bark. This resulted in a situation in which for many years the It was in this setting that Charles Louis Alphonse Laveran (1845–1922), a student of Pasteur Netherlands East India cinchona plantations have produced 97 percent of the total global and a French military doctor based in a hospital in Algeria, started searching for the causative 80, 81 production while British India has produced 2.5 percent and the rest of the world 0.5 percent. agent (Cox 2010). By means of the autopsy of malaria patients and examining lesions For a long time the Dutch held a monopoly on cinchona bark. The use of the cinchona bark of affected organs and blood, he found that the only constant factor was the presence of 82, 83 enabled settlers and explorers to enter dangerous malarial areas and therefore to some extent granules of black pigment in the blood . He examined fresh unstained blood of hundreds facilitated imperial expansion by Western powers. The active antimalarial principle from the of patients and observed ‘‘several different forms of erythrocytic organism including bark, quinine (from kina-kina, Quechua for ‘‘barks of barks’’), is now chemically crescents, spherical motionless bodies with pigment, spherical moving bodies with pigment synthesized and is, along with artemisinins, one of the most effective and potent drugs. and bodies that extruded flagella-like structures all of which he thought were on the outside of the red cells’’80. He noticed these in all patients, but never in those without malaria. Furthermore, he noted that quinine removed these stages from the blood. On November 6, Discovery of Chloroquine and Mefloquine 1880, he observed a motile parasite in blood from a malaria patient. What he saw was the exflagellation of the parasite, later identified as the male gametocyte, a phase in the life cycle Chloroquine was discovered by Johann ‘‘Hans’’ Andersag (1902–1955) at the Bayer of the parasite that normally occurs in the midgut of the Anopheles mosquito. Laveran laboratories in Elberfeld, Germany77. In July 1934 Andersag chemically modified atabrine realized he had discovered the causative parasitic protozoan, which he named Oscillaria by replacement of a part with a quinoline ring77. The drug was initially named resochin. The malariae80. His theory was not readily accepted by eminent microbiologists or malariologists drug was shelved for more than ten years and not used in practice because it was considered of his time, but he did convince the Italian malariologists Camillo Golgi (1843–1926), too toxic for practical use in humans (it was tested against blood-induced P. vivax malaria Amico Bignami (1862–1929), and Ettore Marchiafava (1847–1935) that malaria was caused in four paretic patients in a psychiatric clinic)78. Finally, during World War II, US by a protozoan and not a bacterium. Later he also convinced leading microbiologists government-sponsored trials unequivocally recognized and established chloroquine as an including Pasteur, Robert Koch, Charles Chamberland (1851–1908), and Pierre Roux effective and safe antimalarial drug. For many years it was the first-line antimalarial drug. (1853–1933)80. The discoveries of Laveran were particularly remarkable because he used

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combination therapies (ACTs) are recommended by the World Health Organization and are However, as for many antimicrobial drugs, eventually (two decades later) drug-resistant the first-line treatment in nearly all malaria-endemic countries. strains developed77. In the second half of the twentieth century, another important antimalarial drug was also developed in a time of war: mefloquine was number 142,490 of a total of 250,000 antimalarial compounds screened during the US Army’s antimalarial drug Quinine from the New World discovery program 79. It was discovered shortly after the Vietnam War in the 1970s, and subsequently marketed worldwide. 2 The curative virtues of the Peruvian bark, also known as Jesuit’s bark, first became known to Europeans about 1630, following the arrival of Spanish Jesuit missionaries in the New 68, 75 ό World . The legendary story that the Countess of Chinch n, wife of the Viceroy of Peru, Discovery of the life cycle of the malaria parasite in humans was cured of her fever by using this bark, which she supposedly later brought to Spain, has been disputed68. It is more likely that this indigenous remedy was discovered by observing With the discovery of bacteria by the Dutch tradesman and scientist Antoni van practices of indigenous Indian herbalists by the Jesuits. Nevertheless, the tree was given the Leeuwenhoek (1632–1723) in the Netherlands in 1676—along with the subsequent generic name cinchona, after the Countess of Chinchόn. The acceptance of the cinchona discoveries of the French chemist and microbiologist Louis Pasteur (1822–1895) and the bark as antimalarial was arduous and slow, and doubts regarding its efficacy lingered for a German physician and microbiologist Robert Koch (1843–1910) in 1878–1879 that many long time68. Many physicians hesitated to use the bark because of the many attributed diseases are caused by microbes (known as the germ theory)—the search for a bacterial toxicities. Yet the rising demand for an effective antimalarial prompted botanical expeditions origin of malaria intensified80. Many studies subsequently searched unsuccessfully for an to the New World by the British and the Dutch76. This was hampered when in the nineteenth infectious agent in marshland soil. century South American countries began outlawing the export of cinchona seeds. After a successful attempt to smuggle the famous Cinchona ledgeriana strain from Bolivia, the South American monopoly was destroyed. Plantations were set up in the British Empire in Alphonse Laveran Discovers the Malaria Parasite India and Ceylon (Sri Lanka) and by the Dutch in Java, the Dutch East Indies, to produce large quantities of the bark. This resulted in a situation in which for many years the It was in this setting that Charles Louis Alphonse Laveran (1845–1922), a student of Pasteur Netherlands East India cinchona plantations have produced 97 percent of the total global and a French military doctor based in a hospital in Algeria, started searching for the causative 80, 81 production while British India has produced 2.5 percent and the rest of the world 0.5 percent. agent (Cox 2010). By means of the autopsy of malaria patients and examining lesions For a long time the Dutch held a monopoly on cinchona bark. The use of the cinchona bark of affected organs and blood, he found that the only constant factor was the presence of 82, 83 enabled settlers and explorers to enter dangerous malarial areas and therefore to some extent granules of black pigment in the blood . He examined fresh unstained blood of hundreds facilitated imperial expansion by Western powers. The active antimalarial principle from the of patients and observed ‘‘several different forms of erythrocytic organism including bark, quinine (from kina-kina, Quechua for ‘‘barks of barks’’), is now chemically crescents, spherical motionless bodies with pigment, spherical moving bodies with pigment synthesized and is, along with artemisinins, one of the most effective and potent drugs. and bodies that extruded flagella-like structures all of which he thought were on the outside of the red cells’’80. He noticed these in all patients, but never in those without malaria. Furthermore, he noted that quinine removed these stages from the blood. On November 6, Discovery of Chloroquine and Mefloquine 1880, he observed a motile parasite in blood from a malaria patient. What he saw was the exflagellation of the parasite, later identified as the male gametocyte, a phase in the life cycle Chloroquine was discovered by Johann ‘‘Hans’’ Andersag (1902–1955) at the Bayer of the parasite that normally occurs in the midgut of the Anopheles mosquito. Laveran laboratories in Elberfeld, Germany77. In July 1934 Andersag chemically modified atabrine realized he had discovered the causative parasitic protozoan, which he named Oscillaria by replacement of a part with a quinoline ring77. The drug was initially named resochin. The malariae80. His theory was not readily accepted by eminent microbiologists or malariologists drug was shelved for more than ten years and not used in practice because it was considered of his time, but he did convince the Italian malariologists Camillo Golgi (1843–1926), too toxic for practical use in humans (it was tested against blood-induced P. vivax malaria Amico Bignami (1862–1929), and Ettore Marchiafava (1847–1935) that malaria was caused in four paretic patients in a psychiatric clinic)78. Finally, during World War II, US by a protozoan and not a bacterium. Later he also convinced leading microbiologists government-sponsored trials unequivocally recognized and established chloroquine as an including Pasteur, Robert Koch, Charles Chamberland (1851–1908), and Pierre Roux effective and safe antimalarial drug. For many years it was the first-line antimalarial drug. (1853–1933)80. The discoveries of Laveran were particularly remarkable because he used

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only fresh blood (without any kind of staining) and a dry objective lens with a maximum The fundamental principle of the transmission of malaria by mosquitoes came to be deemed magnification of x400. In the search for malaria parasites in animals, by accident, the possible only when Manson (considered by many as the father of tropical medicine) methylene blue-eosin stain was discovered by the Russian physician Dimitri Leonidovich demonstrated in 1878 that the parasite for elephantiasis (Bancroft’s filaria) could infect a Romanowsky (1861–1921) in 189184. This would serve as the basis for blood staining mosquito. Working with the hypothesis of Manson and Laveran that mosquitoes were methods developed later by others. Staining methods could not only be used for malaria, but involved in the transmission of malaria between humans, Ross made his most important also for other tropical diseases and is therefore a most significant breakthrough in the history discovery on August 20, 189780. While dissecting a culicine mosquito, he found the avian of parasitology. For Laveran’s extensive work on protozoa, he was awarded the Nobel Prize malaria parasite Plasmodium relictum in the stomach tissue of the mosquito. Using the in Physiology or Medicine in 190785. microscope, Ross also identified the malaria parasite by its darkly pigmented cells (now known as haemozoin, the black malaria pigment, derived from discomposed haemoglobin) 92. Using an experimental malaria model in birds, he demonstrated in 1898 that the parasite Naming of the disease developed in mosquitoes and migrated to its salivary glands, allowing the infected mosquito to infect other birds during consecutive bites. He argued that human malaria parasites, Camillo Golgi, an Italian neurophysiologist, had observed in 1885–1886 that there were at analogous to the avian model, are also transmitted by mosquitoes93. However, because of least two separate types of malaria: tertian (48-hour periodicity) and quartan (72-hour military duties (he was sent to India to investigate an epidemic of plague) he was not allowed periodicity). The causing organisms were later called Plasmodium vivax and Plasmodium to test his theory at that time. The incrimination of mosquitoes as vectors in human malaria malariae. He also established that the two forms produced differing amounts of merozoites was demonstrated shortly after the discoveries of Ross by the Italian scientists Giovanni into the bloodstream upon maturity and that the fever coincided with the rupture and release Battista Grassi, Amico Bignami, Giuseppe Bastianelli, Angelo Celli, Camillo Golgi, and of merozoites into the blood stream. Finally, he observed that the severity of symptoms Ettore Marchiafava80, 94. They demonstrated the complete sporogonic cycle of Plasmodium 80 correlated with the number of parasites in the blood . The Italian malariologists Giovanni falciparum, P. vivax, and P. malariae with experiments involving Anopheles claviger Battista Grassi (1854–1925) and Raimondo Feletti (1887–1927) first introduced the names mosquitoes fed on malarial patients and subsequently transmitted the disease to healthy 86 of Plasmodium vivax and Plasmodium malariae in 1890 . This was in contrast with the individuals via the bite of these mosquitoes. Later on they proved that only female Anopheles belief of Laveran that there was only one species, Oscillaria malariae. The malignant tertian mosquitoes could transmit malaria. The mosquito-vector link was established beyond malaria was named Plasmodium falciparum by an American physician and bacteriologist, doubt68. Meanwhile, Ross had been posted to Sierra Leone where, in 1899, he tested and William Henry Welch (1850–1934). In West Africa in 1918 the British physician John confirmed his hypothesis and the discoveries of his Italian colleagues. The discovery made William Watson Stephens (1865–1946) discovered and named a fourth species that by Ross that a vector taking a blood meal from an infected host, to transmit this parasite 87 resembled Plasmodium vivax, which he described as Plasmodium ovale in 1922 . somewhat later to a healthy host, would be one of the most far-reaching scientific insights Plasmodium knowlesi, a zoonotic malaria species, was first described by Robert Knowles to date. It took other scientists quite some time to realize that other diseases such as and Biraj Mohan Das Gupta in 1932 in wild-caught primates. The first documented human onchocerciasis, filariasis, loiasis, African trypanosomiasis, leishmaniasis, and others were 88 infection with Plasmodium knowlesi was in 1965 , and until 1971 only two cases had been transmitted by the bite of infected flies and mosquitoes. In 1902 Ross received the Nobel described. Since 2004 several hundred cases of human infections have been reported, mainly Prize in Physiology or Medicine for his work on malaria. The complete life cycle as we 89 from Malaysia and other parts of Southeast Asia . understand it from the ground-breaking contributions described above is depicted in Figure 2 (next page).

Ross’s discovery that mosquitoes transmit malaria parasites

Despite Laveran’s flagellum discovery, the transmission conundrum of the malaria parasite was yet to be unravelled. The solution to the problem of transmission was due in very large part to the efforts of Ronald Ross (1857–1932), a British doctor working with avian malaria parasites in India68. However, enormous credit is due to the Scottish physician Sir Patrick Manson (1844–1922), who played a pivotal role in providing the scientific background that eventually led to Ross’s accomplishments90, 91.

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only fresh blood (without any kind of staining) and a dry objective lens with a maximum The fundamental principle of the transmission of malaria by mosquitoes came to be deemed magnification of x400. In the search for malaria parasites in animals, by accident, the possible only when Manson (considered by many as the father of tropical medicine) methylene blue-eosin stain was discovered by the Russian physician Dimitri Leonidovich demonstrated in 1878 that the parasite for elephantiasis (Bancroft’s filaria) could infect a Romanowsky (1861–1921) in 189184. This would serve as the basis for blood staining mosquito. Working with the hypothesis of Manson and Laveran that mosquitoes were methods developed later by others. Staining methods could not only be used for malaria, but involved in the transmission of malaria between humans, Ross made his most important also for other tropical diseases and is therefore a most significant breakthrough in the history discovery on August 20, 189780. While dissecting a culicine mosquito, he found the avian 2 of parasitology. For Laveran’s extensive work on protozoa, he was awarded the Nobel Prize malaria parasite Plasmodium relictum in the stomach tissue of the mosquito. Using the in Physiology or Medicine in 190785. microscope, Ross also identified the malaria parasite by its darkly pigmented cells (now known as haemozoin, the black malaria pigment, derived from discomposed haemoglobin) 92. Using an experimental malaria model in birds, he demonstrated in 1898 that the parasite Naming of the disease developed in mosquitoes and migrated to its salivary glands, allowing the infected mosquito to infect other birds during consecutive bites. He argued that human malaria parasites, Camillo Golgi, an Italian neurophysiologist, had observed in 1885–1886 that there were at analogous to the avian model, are also transmitted by mosquitoes93. However, because of least two separate types of malaria: tertian (48-hour periodicity) and quartan (72-hour military duties (he was sent to India to investigate an epidemic of plague) he was not allowed periodicity). The causing organisms were later called Plasmodium vivax and Plasmodium to test his theory at that time. The incrimination of mosquitoes as vectors in human malaria malariae. He also established that the two forms produced differing amounts of merozoites was demonstrated shortly after the discoveries of Ross by the Italian scientists Giovanni into the bloodstream upon maturity and that the fever coincided with the rupture and release Battista Grassi, Amico Bignami, Giuseppe Bastianelli, Angelo Celli, Camillo Golgi, and of merozoites into the blood stream. Finally, he observed that the severity of symptoms Ettore Marchiafava80, 94. They demonstrated the complete sporogonic cycle of Plasmodium 80 correlated with the number of parasites in the blood . The Italian malariologists Giovanni falciparum, P. vivax, and P. malariae with experiments involving Anopheles claviger Battista Grassi (1854–1925) and Raimondo Feletti (1887–1927) first introduced the names mosquitoes fed on malarial patients and subsequently transmitted the disease to healthy 86 of Plasmodium vivax and Plasmodium malariae in 1890 . This was in contrast with the individuals via the bite of these mosquitoes. Later on they proved that only female Anopheles belief of Laveran that there was only one species, Oscillaria malariae. The malignant tertian mosquitoes could transmit malaria. The mosquito-vector link was established beyond malaria was named Plasmodium falciparum by an American physician and bacteriologist, doubt68. Meanwhile, Ross had been posted to Sierra Leone where, in 1899, he tested and William Henry Welch (1850–1934). In West Africa in 1918 the British physician John confirmed his hypothesis and the discoveries of his Italian colleagues. The discovery made William Watson Stephens (1865–1946) discovered and named a fourth species that by Ross that a vector taking a blood meal from an infected host, to transmit this parasite 87 resembled Plasmodium vivax, which he described as Plasmodium ovale in 1922 . somewhat later to a healthy host, would be one of the most far-reaching scientific insights Plasmodium knowlesi, a zoonotic malaria species, was first described by Robert Knowles to date. It took other scientists quite some time to realize that other diseases such as and Biraj Mohan Das Gupta in 1932 in wild-caught primates. The first documented human onchocerciasis, filariasis, loiasis, African trypanosomiasis, leishmaniasis, and others were 88 infection with Plasmodium knowlesi was in 1965 , and until 1971 only two cases had been transmitted by the bite of infected flies and mosquitoes. In 1902 Ross received the Nobel described. Since 2004 several hundred cases of human infections have been reported, mainly Prize in Physiology or Medicine for his work on malaria. The complete life cycle as we 89 from Malaysia and other parts of Southeast Asia . understand it from the ground-breaking contributions described above is depicted in Figure 2 (next page).

Ross’s discovery that mosquitoes transmit malaria parasites

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Anopheles mosquito’s stomach (midgut) is known as the sporogonic cycle. In the mosquito’s stomach cavity the microgametes penetrate the macrogametes, generating zygotes by fusion and meiosis (7). The zygotes become motile and enlarged (ookinetes) and this form penetrates the midgut wall (8) of the mosquito where it develops into oocysts. The oocysts grow, burst, and release numerous sporozoites into the coelomic cavity of the mosquito (9). The sporozoites then make their way to the mosquito's salivary glands awaiting the mosquito to start feeding on another human host.

Consequences for Malaria Control.

The discovery of the role of Anopheles mosquitoes provided new and effective tools for the fight against malaria. Grassi conducted a classical experiment in a malarious area in Italy, protecting 112 volunteers from mosquito bites between dusk and dawn and demonstrating that only five of them developed clinical malaria compared with 415 mosquito-exposed individuals who all developed the disease95. Hence the first weapon of controlling the disease was demonstrated to be extremely effective. Subsequently, other choices of the vector control menu were developed, such as the use of chemical larvicides (use of oils), biological control (larvivorous fish, biological larvicides), environmental source reduction (draining swamps and other mosquito habitats), and personal protection (bed-nets, insect repellents)68.

Mechanism of action of disease

The clinical manifestations of malaria vary with geography, epidemiology, immunity, and age. Understanding the complex pathogenesis of malaria requires exploring mechanisms for parasite invasion and host immune response96. The pathogenesis of Plasmodium falciparum Figure 2. Courtesy of H. Visser-Berenschot, 2012. Adapted and modified from AJ Cann. Original is the most studied, since this species causes the most severe clinical disease, highest image from: http://www.flickr.com/photos/ajc1/6174379207/ (CC BY-SA 2.0) Malaria in humans is caused by five different Plasmodium species (Plasmodium falciparum, Plasmodium vivax, parasitemias, and has a high mortality rate. Other forms are rarely fatal. Plasmodium Plasmodium ovale, Plasmodium malariae and the zoonotic Plasmodium knowlesi), all of which share knowlesi malaria, endemic in localized areas in Southeast Asia, can also cause fulminant essentially similar life cycles (Figure 2). Infection begins when, via a bite and blood meal, disease. As described above, the plasmodial life cycle consists of an exoerythrocytic sporozoites are entering the blood stream from the salivary glands of an infected female Anopheles (asymptomatic) stage and an erythrocytic (symptomatic) stage. The discovery of a liver stage mosquito (1) and travel to the liver where they invade hepatocytes (liver cells) (2). There they before malaria enters the bloodstream was made by the British protozoologists Henry E. undergo asexual multiplication resulting in thousands of daughter merozoites (new parasites) Shortt (1901–1994) and Percy Cyril Claude Garnham (1901–1994) in 1948 97. The existence released into the bloodstream (3). This process, “exoerythrocytic schizogony”, is asymptomatic. of dormant stages in Plasmodium vivax was shown in 1982 by the Polish-American Some sporozoites develop into ‘hypnozoites’ (Plasmodium vivax and Plasmodium ovale only) which physician and scientist Wojciech A. Krotoski (1937– ) and his international team98. are dormant forms that may resume replication after a period of months or years to cause relapses of Plasmodium falciparum malaria differs from the so called benign malarias in several ways: malaria. In the bloodstream, the sporozoites invade red blood cells where they initiate a second phase it affects all red blood cells, digesting haemoglobin and making the cell wall less deformable, of asexual multiplication (4). This results in the production of new merozoites which invade other thus resulting in haemolysis and/or splenic clearance (anaemia). Furthermore, endothelial red blood cells (5). This stage of ”erythrocytic schizogony” (from Greek ‘schizein’ – to divide), is repeated continuously and is responsible for the disease, malaria. During the infection, the binding of Plasmodium falciparum–infected red blood cells leads to sequestration within gametocytes, male (microgametocytes) and female (macrogametocytes) are produced (6) which are small blood vessels, which results in blood flow obstruction, inflammation, and endothelial ingested during a subsequent mosquito blood meal. The parasites’ sexual multiplication in the female barrier breakdown. Microvascular disease due to cytoadherence (formation of sticky knobs

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Consequences for Malaria Control.

Mechanism of action of disease

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on the red blood cell surface and rosetting) of infected erythrocytes to endothelial cells lining the blood vessels, permitting sequestration, is fairly well understood99. Although not described here, research into cerebral malaria has provided some insights and many theories, but we still have limited understanding on the pathogenesis of cerebral malaria, anaemia in malaria, and placental malaria. Based on concepts of pathophysiology, several adjuvant treatments have been recommended for cerebral malaria; however, none of those have stood the test of time.

Renewed optimism

The fascinating quest of malariology’s early heroes, unravelling the mysteries of the plasmodia causing malaria, has paved the way for generations of scientists helping us to better understand malaria in order to fight it most efficiently. We are currently witnessing renewed optimism that malaria control can be optimized to a degree coming close to its elimination from many areas, on a global scale. While the success depends on sustained scientific, economic, and political commitment, we may be able to succeed in pushing back malaria on an unprecedented scale, with a mixed approach to malaria control encompassing optimized prevention measures, better tools to diagnose the disease, novel drugs to treat it efficiently and keep the development of drug resistance at bay, and possibly even a vaccination.

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