Toxoplasmosis Life Cycle

(from CDC Division of Parasitic Diseases)

Members of the cat family 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 eating infected meat . 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 (i.e. become infective). Although cats shed oocysts for only 1 to 2 weeks, large numbers may be shed during this time. 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 cysts ; B) ingestion of the oocyst from fecally contaminated hands or food ; C) organ transplantation or blood transfusion; D) transplacental transmission. The parasites form tissue cysts, most commonly in skeletal muscle, myocardium (heart muscle), and brain; these cysts may remain throughout the life of the host.

Last reviewed: 25 August 2011