Parasitic promastigotes that cause leishmaniosis in humans (Leishmania donovani), coloured scanning electron micrograph (SEM). This tropical disease is transmitted by bites from infected sand flies. They are ingested by the insect vector during a blood meal from a mammal or human. The parasites in humans are found within macrophages in the amastigote form. In the blood stream they transform into the promastigote form. Promastigotes multiple by longitudinal fission in the gut of the insect. Leishmaniosis occurs in two forms: cutaneous which affects the skin and mucous membranes, usually giving rise to an ulcer at the site of the insect bite. The more serious kala- azar causes fever and liver damage, and it can be fatal. Magnification: x1,000 when shortest axis printed at 25 millimetres.
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