How does a sandfly cause leishmaniasis?

A sandfly causes leishmaniasis by acting as a vector for the Leishmania parasites. When a female sandfly bites a human, it injects the parasites into the bloodstream through its saliva. The parasites then invade and multiply within the host's immune cells, leading to various forms of leishmaniasis, which can affect the skin, mucous membranes, or internal organs. Transmission typically occurs in tropical and subtropical regions where sandflies are prevalent.