L. infantum life cycle. (1) During the bloodmeal from an infected vertebrate host, the female sandfly ingests free amastigotes, as well as intracellular amastigotes. In the midgut of the sandfly the amastigotes transform into procyclic promastigotes. (2) The procyclic promastigotes multiply and transform into metacyclic promastigotes, the infective stage, that migrate towards the buccal cavity of the sandfly. (3) A bite from the sandfly transmits Leishmania promastigotes to susceptible mammalian hosts (i.e., humans and dogs). (4) Promastigotes invade macrophages and DCs. Within these host cells, promastigotes transform into intracellular amastigotes and replicate to produce a large number of parasites. (5) Consequently, the infected cell ruptures and releases amastigotes into the circulation. (6) Free amastigotes can infect other mononuclear phagocytic cells of the blood, spleen, liver, lymph nodes and bone marrow, and the life cycle is repeated.