Leishmania protozoa. Light micrograph of Leishmania donovani protozoa. L. donovani is a single-celled organism which causes visceral leishmaniasis (kala-azar) in humans. There are two main forms of the organism, one occurring in humans and one in the sandfly. The flagellated promastigote form seen here is found in the saliva of the sandfly, and is passed to humans when the sandfly feeds on blood. Once inside the human host, the protozoa change into the amastigote form, which causes destruction of tissues such as the liver and spleen. Without drug treatment, kala-azar can be fatal. Magnification unknown.
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