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Members of the cat
family (Felidae) are the only known definitive hosts for the sexual stages
of T. gondii and thus are the main reservoirs of infection. Cats
become infected with T. gondii by carnivorism
. After
tissue cysts or oocysts are ingested by the cat, viable organisms are
released and invade epithelial cells of the small intestine where they
undergo an asexual followed by a sexual cycle and then form oocysts, which
are excreted. The unsporulated oocyst takes 1 to 5 days after excretion to
sporulate (become infective). Although cats shed oocysts for only 1 to 2
weeks, large numbers may be shed. Oocysts can survive in the environment
for several months and are remarkably resistant to disinfectants, freezing,
and drying, but are killed by heating to 70°C for 10 minutes. Human infection may be acquired in several ways: A) ingestion of undercooked infected meat containing Toxoplasma cysts ; B) ingestion of the oocyst from fecally contaminated hands or food ; C) organ transplantation or blood transfusion; D) transplacental transmission; E) accidental inoculation of tachyzoites. The parasites form tissue cysts, most commonly in skeletal muscle, myocardium, and brain; these cysts may remain throughout the life of the host.
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