Infection of phlebotomine sandflies with Leishmania

Abstract

Species of sandflies that are capable of transmitting leishmaniasis are found in two genera: Lutzomyia and Phlebotomus. Only the females blood-feed and transmit disease via their bite, Lutzomyia species in the Americas, and Phlebotomus spp. elsewhere. Under natural conditions each species of sandfly is usually the vector for a single species of Leishmania. In female sandflies Leishmania parasites exist as extracellular flagellated promastigote forms and are found exclusively in the alimentary canal. In the majority of cases the parasites cycle between their sandfly hosts and certain wild mammals, with human infection a zoonosis. However, there are some important exceptions in which there is a human host-sandfly cycle; visceral leishmaniasis in India, for example. In their mammalian hosts Leishmania parasites exist as nonmotile intracellular amastigote forms in tissue macrophages. The parasites cause two main types of human disease: visceral leishmaniasis and cutaneous leishmaniasis. Since the taxonomy of both phlebotomine sandflies and Leishmania, and their host-parasite relationships, are all subjects of current research, the precise number of naturally occurring parasite-sandfly combinations remains to be determined. Currently there are approximately 70 proven or suspected vectors of leishmaniasis (Lane, 1993) and 20 or so recognized species of Leishmania (Lainson and Shaw, 1987).