Toxoplasma gondii is a species of parasitic protozoa in the genus Toxoplasma.The definitive host of T. gondii is the cat, but the parasite can be carried by many warm-blooded animals. Toxoplasmosis, the disease of which T. gondii is the causative agent, is usually minor and self-limiting but can have serious or even fatal effects in two populations: The first of these is immunodeficient subjects (e.g. with AIDS) in whom the infection can reactivate in the lungs or the central nervous system. The second is pregnant women infected for the first time. Classically, infection of the embryo is rare but when it occurs it can have dire consequences. Symptoms range from none to benign lymphadenopathy (a mononucleosis-like illness) to life-threatening CNS disease or involvement of other organs in immunocompromised people. Retinochoroiditis, seizures, and intellectual disability occur in congenital infection.