Toxoplasma gondii

This is a cosmopolitan protozoan parasite. Cats are its definitive hosts, and various mammals and birds can serve as intermediate hosts. Mature oocysts swallowed by the intermediate hosts transform into tachyzoites (a rapidly multiplying stage), which migrate throughout the body where they form cysts.
Human infection occurs by ingestion either of cysts in raw or undercooked meat or of oocysts from cat feces. In most cases the infection is asymptomatic, but it sometimes causes encephalitis and vision problems. A first infection during pregnancy can result in transmission to the fetus through the placenta, and may cause abortion or hydrocephalus.