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- Sexual reproduction of T. gondii apparently occurs only in cats. After the cat ingests a tissue cyst in food, the cyst breaks down to release bradyzoites which reproduce in the wall of the intestine, eventually giving rise to oocysts which are passed out in the faeces.
- The oocyst further develops for 24 hours or more (depending on environmental temperature) before infectious sporozoites form.
- Only sporulated oocysts are infectious.
- Ingestion of sporulated oocysts by an intermediate host (e.g. rodent, dog, man or sheep) leads to release of sporozoites which penetrate the intestinal wall, multiply asexually as tachyzoites, become widely disseminated and encyst in tissues.
- The cycle is completed when a cat eats cysts in an intermediate host. Toxoplasmosis can also be transmitted between non-feline hosts if one eats the other (e.g. dog or man eating infected sheep meat).
- There is also some evidence that transplacental transmission of tissue cysts may occur in some rodent species.
- Most cats become infected by ingestion of tissue cysts in prey (e.g. rodents) or other food (raw meat). Shedding of oocysts in faeces is most common in kittens, but can occur in any age of cat (and may be enhanced by, for example, feline immunodeficiency virus infection).
- Oocysts can remain infectious for several months and are quite resistant to disinfectants, drying and freezing. Tissue cysts are less resistant, and are destroyed by proper cooking of food.
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