An infected triatomine assassin bug takes a blood meal and releases trypomastigotes (the characteristic infective developmental stage) in its feces near the site of the bite wound. Trypomastigotes enter the host through the wound or through intact mucosal membranes, such as the conjunctiva. Inside the host, the trypomastigotes invade cells near the site of inoculation, where they differentiate into intracellular amastigotes (a developmental stage without visible external flagella or cilia). The amastigotes multiply by binary fission and differentiate into trypomastigotes, which are then released into the circulation as bloodstream trypomastigotes. Trypomastigotes infect cells from a variety of tissues and transform into intracellular amastigotes in new infection sites. Clinical manifestations can result from this infective cycle. The bloodstream trypomastigotes do not replicate (in contrast to the trypanosomes that cause African Sleeping Sickness). Replication resumes only when the parasites enter another cell or are ingested by another vector. The triatomine bug becomes infected by feeding on human or animal blood that contains circulating parasites. The ingested trypomastigotes transform into epimastigotes in the vector’s midgut. The parasites multiply and differentiate in the midgut and differentiate into infective metacyclic trypomastigotes in the hindgut. Common triatomine vector species for trypanosomiasis belong to the genera Triatoma, Rhodnius, and Panstrongylus. Trypanosoma cruzi can also be transmitted through blood transfusions, organ transplantation, transplacentally, and in laboratory accidents. (Centers for Disease Control Parasites and Health website)
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