The ecology of toxoplasmosis

Toxoplasma infection comes from oöcysts in cat faeces and from tissue cysts in the flesh of infected animals. It can also be transferred congenitally by trophozoites. Where cats are common, where social, climatological and geological conditions favour the survival and maturation of oöcysts, and where raw or undercooked meat is rarely eaten infection comes predominantly from oöcysts. Where raw or undercooked meat is commonly eaten and opportunities for contact with cats and their faeces are few, infection comes predominantly from tissue cysts. Infection is very common in all species of mammals and birds throughout the world, but rarely does any harm. Exceptions are when lowered resistance due to disease or cytotoxic or immunosuppressive drugs allow latent infection to become patent and when infection is transmitted congenitally.