ABSTRACT
PATHOPHYSIOLOGY TG can infect any mammal, which serves as an intermediate host. The definitive host is the cat (only one that can support both sexual and asexual reproduction). The parasite can exist as
1. Trophozoite (invasive form) 2. Cyst (latent form) 3. Oocyst (only in cats)
Sexual reproduction occurs in the small intestine of the cat that has eaten tissue cysts containing TG. Only during this first exposure is the cat infectious as these oocysts are produced for two weeks and contain infectious sporozoites. The oocysts require one to five days to become infected, and after two weeks, the cat is not infectious and becomes immune. Oocysts can remain infectious for years in soil. Human infection starts with ingestion (from food, water, hands, or insects) of cysts from uncooked/undercooked meat of infected animals (e.g., lamb and mutton) or contact with oocysts from infected cats (who get it from infected mice, etc.) or contaminated soil. The infected oocysts become infective inside the pregnant woman in 4 to 10 (average 7) days, leading to parasitemia. Eventually, TG can infect and live forever in striated muscle or brain. Only a very few cases of congenital toxoplasmosis transmitted by mothers who were infected prior to conception have been reported; they can be attributed to either reinfection with a different strain or to reactivation of chronic disease. This reactivation is very rare but can occur, especially in an immunocompromised woman. Immunocompetent women with prior toxoplasmosis can be reassured that the risks to the subsequent fetus/neonate are miniscule, especially >9 months after infection [4].
