Leishmania Development in Sand Flies and Main Aspects of This Parasite-vector Interaction

Leishmaniases are important vector-borne disease with a wide range of clinical symptoms in humans and domestic animals. Leishmania species infecting humans are transmitted by phlebotomine sand flies belonging to genera Phlebotomus and Lutzomyia. Here we summarize main aspects of Leishmania development in sand flies. In the vector, Leishmania development is confined to the digestive tract, mainly midgut, where parasites encounter various mechanical or biochemical barriers. The first one is mounted by a proteolytic attack by digestive proteases secreted following a bloodmeal. A second barrier is presented by peritrophic matrix surrounding the bloodmeal. At the end of bloodmeal digestion, when peritrophic matrix breaks, Leishmania must attach to midgut epithelium to prevent excretion with the remnants of the bloodmeal. In matured infections parasites migrate towards the thoracic midgut, destroy the stomodeal valve and produce promastigote secretory gel which blocks the midgut lumen. Blocked sand flies have problem to take a bloodmeal, bite repeatedly, increasing the chance of Leishmania transmission. Finally, parasites are injected into the vertebrate host together with PSG and sand fly saliva. Metacyclic promastigotes deposited into the host skin are swallowed by the phagocytic cells, mainly macrophages, and inside them transform to non-flagellated amastigotes.