Leishmanias – Flagellates
Species of the genus Leishmania are parasites of mammals including man. Leishmanias infections occur over wide regions of the world from Asia, the near and middle East to East and West Africa and from Mexico to the northern part of Argentina.Sandflies (Phlebotomus or Lutzomia species) serve as vectors for all species of Leishmania.
The parasite is flagellated in sandfly. During its blood meal, the fly introduces the parasite into the skin of the mammalian host. The wandering macrophages engulf these parasites. In the host cell they lose the free flagellum and become rounded. The parasites multiply by repeated binary fission, emerge from the host cell by destroying it and invade newer macrophages to repeat the propagative cycle. When a sandfly feeds on the blood of an infected vertebrate, it also ingests the infective stage of Leishmania. Leishmania species cause a wide range of disease. L. donovani, which is widely distributed in some regions of Latin America, causes a serious and fatal disease, kala-azar or visceral leishmaniasis -involving liver and spleen. In Assam, 25 per cent of the population was deleted between 1890 to 1900 due to kala-azar.
Figure:(a) Leishmania donovani in macrophages (b) Child with swollen abdomen due to enlarged spleen
Sometimes severe dermal infection appears in those individuals who have earlier had kala-azar infection. Ltropica which mainly occurs in the West and Central India and arid regions of the eastern hemisphere, causes cutaneous leishmaniasis or oriental sores. This is a mild disease in which at the site of each bite by the fly, a small ulcer is produced.