Toxoplasma gondii, a single-celled parasite, causes the disease toxoplasmosis. The life cycle of Toxoplasma gondii includes two phases: the intestinal (or enteroepithelial) and extraintestinal phases. The intestinal phase produces oocysts and occurs only in wild and domesticated cats. The extra-intestinal phase occurs in all infected animals and produces tachyzoites (actively proliferating trophozoites) and, eventually, bradyzoites (slowly growing trophozoites) or zoitocysts. Toxoplasma gondii infects tissue of the gastrointestinal tract, brain and lung in immunocompromised patients.