Leishmaniasis is a vectorborne disease that is transmitted by sand flies and caused by obligate intracellular protozoa of the genus Leishmania. Human infection is caused by more than 20 species. These include the L. donovani complex with 2 species (L. donovani, L. infantum [also known as L. chagasi in the New World]); the L. mexicana complex with 3 main species (L. mexicana, L. amazonensis, and L. venezuelensis); L. tropica; L. major; L. aethiopica; and the subgenus Viannia with 4 main species (L. [V.] braziliensis, L. [V.] guyanensis, L. [V.] panamensis, and L. [V.] peruviana). The different species are morphologically indistinguishable, but they can be differentiated by isoenzyme analysis, molecular methods, or monoclonal antibodies.
Leishmaniasis is transmitted by the bite of infected female phlebotomine sand flies. The sand flies inject the infective stage (i.e., promastigotes) from their proboscis during blood meals
. Promastigotes that reach the puncture wound are phagocytized by macrophages
and other types of mononuclear phagocytic cells. Promastigotes transform in these cells into the tissue stage of the parasite (i.e., amastigotes)
, which multiply by simple division and proceed to infect other mononuclear phagocytic cells
. Parasite, host, and other factors affect whether the infection becomes symptomatic and whether cutaneous or visceral leishmaniasis results. Sand flies become infected by ingesting infected cells during blood meals (
). In sand flies, amastigotes transform into promastigotes, develop in the gut
(in the hindgut for leishmanial organisms in the Viannia
subgenus; in the midgut for organisms in the Leishmania
subgenus), and migrate to the proboscis
Life cycle image and information courtesy of DPDx.