The immunology of Toxoplasma gondii infection in the immune-competent host

The protozoan parasite Toxoplasma gondii (T. gondii) is one of the most common parasites of humans, with clinical toxoplasmosis constituting a major risk to immuno-compromised individuals, pregnant women and unborn children [1]. T. gondii infection is common in most war en blooded vertebrates and infects approximately 15–80% of the world’s human population depending on ethnicity or geographical location [2]. The sexual stage of the life cycle takes place in the intestine of the definitive host, the cat. Transmission to the intermediate host can occur in several ways — ingestion of infective sporulated oocysts released in cat faeces, or by the ingestion of meat containing the long-lived tissue cyst stage which allows direct transmission from one intermediate host to another. Vertical transmission results in congenital infection or more unusually, infection can be acquired as a result of receiving transplants from infected individuals or occasionally as a result of a laboratory accident.