Life Cycle Of Human African Trypanosomiasis

African trypanosomes are extracellular organisms, both in the mammalian and insect

host. Infection in the human host begins when the infective stage, known as the metacyclic

stage, is injected intradermally by the tsetse fly. The organisms rapidly transform into

blood-stage trypomastigotes (long, slender forms), and divide by binary fission in the

interstitial spaces at the site of the bite  wound. The buildup of metabolic wastes and cell

debris leads to the formation of a chancre.