Ourpresent Knowledge of the Ecology and Controlof Leishmaniasis in the Amazon Region of Brazil

Species of Leishmania Ross, 190349, are exclusively parasitic protozoa of the Order Kinetoplastida, Family Trypanosomatídae. They are digenetic (heteroxenous) organisms, with promastigotes and paramastigotes (with a single, free flagellum) in the alimentary tract of the insect host, and round-oval amastigotes (no free flagellum) in the macrophages of vertebrate hosts: as far as is known there is no sexual stage in the parasite’s lifecycle. The insect hosts appear to be limited to species of the haematophagous phlebotomine “sandflies” (Diptera: Psychodidae: Phlebotominae), and the vertebrate hosts to a variety of mammals. The latter function as reservoirs of infection for the sandfly, and transmission to the next mammalian host is predominantly by injection of the parasite during the bite of the infected insect. The primitive nature of the promastigote form has led to the widely adopted view that the sandfly vectors of Leishmania (or their ancestors) represent the primitive and primary hosts of the parasite: a suggestion which finds support in a definite cycle of development which takes place within the sandfly gut, and sometimes attached to the gut wall. Leishmania probably adapted to survive in mammals, after the inoculation of the organism during the evolution of the blood-sucking habit of ancestral sandflies. The mam­ malian hosts now act not only as a supply of blood for the sandfly, but as a source of infection from the amastigotes located in the skin or blood of these animais. A large number of mammalian species act as reservoirs of Leishmania. The parasites are commonly found in rodents, canids, marsupiais, edentates, procyonids, primitive ungulates (hyraxes) and primates; rare infections have even been recorded in bats. No leishmanias have yet been recorded in amphibians or birds (although there are some sandfly species which feed on these animais), and Leishmania -like parasites of reptiles (Sauroleishmania) have now been removed from the genus Leishmania.