Definition: A genus of digenetic, asexual, protozoan flagellates (family Trypanosomatidae) that occur as amastigotes in the macrophages of vertebrate hosts, and as promastigotes in invertebrate hosts and in cultures. Species are largely indistinguishable morphologically but may be distinguished by clinical manifestations, geographic distribution and epidemiology, developmental patterns of promastigotes in their sandfly hosts, virulence testing of clones in vivo, the effect of test sera on growth in culture, cross-immunity tests, and serotyping with promastigote excreted factors; strains also can be distinguished by various biochemical analyses and DNA sequencing. Such procedures have identified all recognized groups and confirmed the separation of New World leishmaniasis agents into two species complexes, Leishmania mexicana and Leishmania braziliensis.
[W. B. Leishman]
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