Toxoplasma gondii start as unsporulated oocysts, turn into sporulated oocysts in the environment, which in turn become tachyzoites when ingested by an animal, states the Centers for Disease Control and Prevention. Once the parasite reaches the tachyzoites phase and infects a host, it then reaches its final form and becomes a tissue cyst.
Unsporulated oocysts are typically found in household cats and their close relatives, states the Centers for Disease Control and Prevention. An infected cat expels unsporulated oocysts in its feces in large quantities. Once in the environment, the oocysts sporulate and become infectious, a process which usually takes one to five days. Water, soil and plant material containing oocycsts infects an animal, such as a bird or rodent, when ingested.
After ingestion by an animal, the oocysts turn into tachyzoites, states the CDC. The tachyzoites embed themselves into the neural and muscle tissue of their host animal, where they then become a tissue cyst called bradyzoites. Another cat, or other animal, comes along and ingests the bradyzoites of the bird, rodent or other animal, and the animal becomes infected with the Toxoplasma gondii. The animal may also become infected by ingesting sporulated oocysts in the environment.
A human may also become infected with the parasite by ingesting infected meat that is undercooked, consuming food or water contaminated with infected cat feces, through an organ transplant or blood transfusion, or a fetus may contact the parasite from its mother, informs the CDC. Tissue cysts typically form in the brain, eyes, myocardium or muscle of the skeleton in humans.