Leishmania species are extracellular, flagellated promastigotes while dwelling in their sandfly vector, but are obligate intracellular, nonflagellated amastigotes while living in vertebrate hosts, including humans.
- Organisms of the L. donovani complex usually cause visceral leishmaniasis and are present in Asia, the Middle East, the horn of Africa, the Mediterranean, and Central and South America.
- L. tropica, L. major, and L. aethiopica cause Old World cutaneous leishmaniasis and are present in Asia and in northern and sub-Saharan Africa.
- The L. mexicana complex causes New World cutaneous leishmaniasis and is present in Central America and northern South America.
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