Microbiology

                                                            Toxoplasma Gondii

The T. gondii life cycle has three stages: tachyzoite, bradyzoite, and sporozoite. During the acute stage of T. gondii infection, tachyzoites invade and replicate within cells and are responsible for congenital infection. The tachyzoites invade all organs, especially the muscles (including the heart), liver, spleen, lymph nodes, and central nervous system (CNS). During latent infection, bradyzoites are present in tissue cysts. Sporozoites are found in environmentally resistant oocysts formed after the sexual stage of the life cycle.

Cats are the definitive hosts for the sexual stage of T. gondii, which takes place in their intestinal mucosa. During acute infection, cats excrete non-infectious oocysts in their feces. Depending on environmental conditions, the oocysts sporulate and become infectious after one day to several weeks. Under favorable conditions (i.e., in warm, moist soil), oocysts remain infectious for a year or more.

T. gondii is transmitted to humans by three principal routes.

 First, humans can acquire T. gondii by eating raw or inadequately cooked infected meat, especially pork, mutton, and wild game, or uncooked foods that have come in contact with infected meat.

Second, humans can inadvertently ingest oocysts that cats have passed in their feces, either from a litter box or from soil.

Third, women can transmit the infection transplacentally to their unborn fetus. In adults, the incubation period for T. gondii infection ranges from 10 to 23 days after the ingestion of undercooked meat and from five to 20 days after the ingestion of oocysts from cat feces.