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An infected triatomine
insect vector (or “kissing” bug) takes a blood meal and releases
trypomastigotes 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
. Common
triatomine vector species for trypanosomiasis belong to the genera
Triatoma, Rhodinius, and Panstrongylus. Inside the host,
the trypomastigotes invade cells, where they differentiate into
intracellular amastigotes
. The
amastigotes multiply by binary fission
and
differentiate into trypomastigotes, and then are 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 (different from the African trypanosomes). Replication
resumes only when the parasites enter another cell or are ingested by
another vector. The “kissing” 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
. Trypanosoma cruzi can also be transmitted through blood transfusions, organ transplantation, transplacentally, and in laboratory accidents. |