Toxoplasmosis, an infection with a worldwide distribution, is caused by the intracellular protozoan parasite, Toxoplasma gondii. Immunocompetent persons with primary infection are usually asymptomatic, but latent infection can persist for the life of the host. However, there is a risk of reactivating infection at a later time should the individual become immunocompromised, even if infection was asymptomatic or only mildly symptomatic initially. (See "Toxoplasmosis in HIV-infected patients".)
Toxoplasmosis in immunocompetent persons will be reviewed here. Toxoplasmosis in HIV-infected and pregnant patients and congenital and ocular toxoplasmosis are discussed separately. (See "Toxoplasmosis and pregnancy" and "Overview of TORCH infections" and "Retinal vasculitis associated with systemic disorders and infections".)
Transmission — Felines are the only animals in which T. gondii can complete its reproductive cycle . Following feline ingestion of any of the forms of T. gondii, the parasite infects the gut epithelial cells and reproduces. The feline then excretes infectious oocysts in feces.
When non-felines, including humans, ingest T. gondii oocysts, the organisms invade intestinal epithelium and disseminate throughout the body. They then encyst in any type of nucleated cell and can lie dormant within tissues for the life of the host.
There are four means of acquiring toxoplasmosis in humans :