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Leishmania donovani
''Leishmania donovani'' is a species of intracellular parasitic protozoan belonging to the genus ''Leishmania'', a group of haemoflagellate kinetoplastids that cause the disease leishmaniasis. It is a human blood parasite responsible for visceral leishmaniasis or ''kala-azar'', the most severe form of leishmaniasis. It infects the mononuclear phagocyte system including spleen, liver and bone marrow. Infection is transmitted by species of sandfly belonging to the genus ''Phlebotomus'' in Old World and ''Lutzomyia'' in New World. Therefore, the parasite is prevalent throughout tropical and temperate regions including Africa (mostly in Sudan), China, India, Nepal, southern Europe, Russia and South America. It is responsible for thousands of deaths every year and has spread to 88 countries, with 350 million people at constant risk of infection and 0.5 million new cases in a year.
''L. donovani'' was independently discovered by two British medical officers William Boog Leishman in Netley, England, and Charles Donovan in Madras, India, in 1903. However, the correct taxonomy was provided by Ronald Ross. The parasite requires two different hosts for a complete life cycle, humans as the definitive host and sandflies as the intermediate host. In some parts of the world other mammals, especially canines, act as reservoir hosts. In human cell they exist as small, spherical and unflagellated amastigote form; while they are elongated with flagellum as promastigote form in sandflies. Unlike other parasitic protists they are unable to directly penetrate the host cell, and are dependent upon phagocytosis. The whole genome sequence of ''L. donovani'' obtained from southeastern Nepal was published in 2011.
==Discovery==
One of the earliest known epidemics of ''L. donovani'' infection (''kala-azar'' as it was called in Hindi) was known in India just after the Indian Rebellion of 1857. The first medical record was however only in 1870 by British medical officers from Assam. In 1900, an English soldier stationed at Dum Dum, West Bengal, died at the Army Medical School in Netley, England. The autopsy was performed by William Boog Leishman. He processed the tissue sample of the enlarged spleen using a staining technique (now known as Leishman's stain) which he had just developed, and discovered the protozoan parasites using microscopy. But he mistakenly considered the parasites to be degenerate trypanosomes, already known protozoan parasites in Africa and South America. In 1903, Leishman published his discovery of "trypanosomes in India" in the ''British Medical Journal'', which appeared on 11 May. Another British medical officer Charles Donovan, who was serving in the Indian Medical Service, had found the parasites in April of that year at the Government General Hospital in Madras. After reading Leishman paper, Donovan confirmed on 17 June that the parasites (by then known as "Leishman bodies") were definitely the causative agents of ''kala-azar''. He wrote a commentary of his discovery in relation to that of Leishman in the same journal, that appeared on 11 July 1903.〔(【引用サイトリンク】url=http://forms.asm.org/Membership/index.asp?bid=17372 )〕 Soon a controversy arose as to whom such a monumental discovery should be credited. Donovan sent some of his slides to Ronald Ross, who was at the time in Liverpool, and to Alphonse Laveran at the Pasteur Institute in Paris. Laveran and his colleague Félix Mesnil identified the protozoan (and yet wrongly) to be members of Piroplasmida, and gave the scientific name ''Piroplasma donovanii''. It was Ross who resolved the conflict of priority in the discovery and correctly identified the species as member of the novel genus ''Leishmania''. He gave the popular name "Leishman-Donovan bodies", and subsequently the valid binomial ''Leishmania donovani'', thereby equally crediting the two rivals.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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