Toxoplasma gondii life cycle
The only known definitive hosts for T. gondii are members of family Felidae (domestic cats and their relatives).
1a. Oocysts are shed in the cat’s feces. Large numbers are shed, but usually only for 1–2 weeks. Oocysts take 1–5 days to sporulate and become infective.
1b. Cats become reinfected by ingesting sporulated oocysts.
2. Soil, water, plant material, or cat litter becomes contaminated with oocysts. Intermediate hosts in nature (eg, birds, rodents, wild game, animals bred for human consumption) become infected after ingesting infective materials.
3. Oocysts develop into tachyzoites shortly after ingestion.
4. Tachyzoites spread throughout the body and form tissue cysts in neural, eye, and muscle tissue.
5. Cats become infected after consuming intermediate hosts containing tissue cysts.
6a. Humans can become infected by ingesting undercooked meat containing tissue cysts.
6b. Humans can become infected by ingesting food or water contaminated with cat feces or other feces-contaminated materials (eg, soil) or contact with a pet cat’s litter.
7. Rarely, human infection results from blood transfusion or organ transplantation.
8. Rarely, transplacental transmission from mother to fetus occurs.
9. In the human host, parasites form tissue cysts, most commonly in skeletal muscle, myocardium, the brain, and the eyes; these cysts may remain throughout the life of the host and can reactivate if the host becomes immunocompromised.