Leishmania

Abstract

Leishmania are vector‐borne parasitic protozoa that cause the human tropical disease leishmaniasis. Over 30 species have been described, with 11 of these being important pathogens. The disease has three main forms: cutaneous, mucocutaneous and visceral leishmaniasis. The parasites undergo a complex developmental cycle in their phlebotomine sand fly vectors leading to the differentiation of infectious metacyclic promastigote forms, and are transmitted by bite. Many species are zoonotic, being maintained in domestic or wild animal reservoir hosts, and the others are anthroponotic and transmitted from human to human. In their mammalian hosts they live as intracellular amastigote forms inside macrophages. There are relatively few drugs available to treat leishmaniasis, and control of the sand fly vectors or reservoir hosts is difficult. The best long‐term solution to the public health challenge of leishmaniasis will be vaccines, and progress is being made, but an effective vaccine for human usage has not been developed yet. Key Concepts Leishmania are intracellular parasites that live in the phagolysosomes of macrophages, a unique location for a eukaryotic pathogen. The different forms of leishmaniasis result from infection of differently located populations of macrophages and the human response to infection. Leishmaniasis is a chronic infection that can be treated, but limited drugs are available and no prophylactic vaccine is yet available for human use. There are many species of Leishmania but all share a common set of molecular, biochemical and cell biological features along with species‐specific properties. There are more sand fly vectors than Leishmania species, but they exist in specific pairs, each parasite being transmitted by one or more particular species of sand fly.