Leishmania donovani

''Leishmania donovani'' is a species of intracellular parasites 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. The species complex it represents is prevalent throughout tropical and temperate regions including Africa , China, India, Nepal, southern Europe, Russia and South America. The species complex 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.

''L. donovani'' ''sensu stricto'' is in a species complex with the closely related ''L. infantum'', which causes the same disease. The former is commonly found in East Africa and the Indian subcontinent, while the latter is found in Europe, North Africa, and Latin America. The split is done in 2007, and references to ''L. donovani'' often still refer to the entire complex .