Leishmaniasis is caused by protozoan parasites belonging to the genus Leishmania. The parasites are transmitted by the bite of a tiny – only 2–3 mm long – insect vector, the phlebotomine sandfly.
There are some 500 known phlebotomine species, but only about 30 have been found to transmit leishmaniasis. Only the female sandfly transmits the parasites. Female sandflies need blood for their eggs to develop, and become infected with the Leishmania parasites when they suck blood from an infected person or animal. Over a period of between 4 and 25 days, the parasites develop in the sandfly. When the infectious female sandfly then feeds on a fresh source of blood, it inoculates the person or animal with the parasite, and the transmission cycle is completed.
Phlebotomine sandflies are found throughout the intertropical and temperate regions of the world.
The female sandfly lays its eggs in the burrows of certain rodents, the bark of old trees, ruined buildings, cracks in the walls of houses, animal shelters and household rubbish, where the larvae can find the organic matter, heat and humidity they need to develop.
In its search for blood (usually in the evening and at night), the female sandfly can cover a distance of up to several hundred metres around its habitat.