The two major sources for the transmission of toxoplasmosis are meat and cat feces. By handling raw meat or eating raw or undercooked meat , a person may ingest parasite cysts and develop the disease. Although any meat source may contain Toxoplasma tissue cysts, pork appears to be the main meat source of infection in the United States. Venison and meat from other wild animals can also be sources of T. gondii cysts, as can unprocessed goat's milk. Infected cats usually shed eggs in their feces for only 1 to 2 weeks during their lives.
Cats develop immunity against the parasite, which usually prevents reinfection.
Because the immune cat is unlikely to become reinfected, it is unlikely that the cat will ever shed eggs again. When eggs are swallowed by other animals or humans, they hatch and multiply within the muscle tissue. These cysts remain in the host's tissues for the lifetime of that animal or person, which also produces immunity to reinfection. Ingestion of only a few eggs may result in no noticeable illness, but immunity may still be developed. Illness is more likely to result when a large number of eggs or tissue cysts are ingested.