Toxoplasma

Toxoplasma gondii is an obligate, intracellular protozoan parasite in the phylum Apicomplexa that is infectious to a wide variety of animals. Approximately 25 to 30% of the world’s population is thought to be infected with T. gondii .The life cycle of T. gondii involves three different forms: rapidly dividing, invasive tachyzoites; slowly dividing cyst bradyzoites; and an environmentally hardy oocyst containing infectious sporozoites. Classically, the T. gondii life cycle alternates between a definitive felid (cat) host and an intermediate host. Cats become infected when they ingest tissue contaminated with T. gondii cysts. These cysts infect enterocytes and undergo sexual reproduction to form the oocysts. Oocysts are excreted in the feces into the environment and internally sporulate, becoming infectious within 2 to 3 days of being released. Infection of the intermediate host (e.g., rodents, herbivores, humans) typically occurs through ingestion of oocysts in contaminated food or water, although humans and other animals can also become infected by eating raw or undercooked meat containing T. gondii cysts. Following ingestion, parasites penetrate the intestinal lining and differentiate into tachyzoites, which can invade virtually any host cell, replicate, and disseminate throughout the body. For approximately 90% of otherwise healthy individuals, infection with T. gondii is entirely asymptomatic. The remaining 10% of patients typically experience self-limiting, nonspecific symptoms, including fever and lymphadenitis, which may last for several weeks and mimic other infectious diseases.