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These parasites[7] (see also  Chapter 77), species of the genus Leishmania, are classified in the same family (Trypanosomatidae) as the trypanosomes. Like them, they alternate between two hosts: a vertebrate and an invertebrate; however, the only forms which develop in the former are intracellular amastigotes, and those which develop in the invertebrate (insect) vector are promastigotes (Figure II.8). Promastigotes are elongate, motile flagellates with the flagellar origin and kinetoplast at the anterior end of the cell and the nucleus more or less in the middle. Both forms divide by binary fission and there is no firm evidence yet of sexual reproduction, although naturally occurring apparently ‘hybrid’ populations have been reported.

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The vectors of all the species of Leishmania which infect humans are small insects (sand flies) of the genera Phlebotomus (in Africa, Asia and Europe) and Lutzomyia and Psychodopygus(in South and Central America); as with mosquitoes, only female …