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----THE BRAIN WORM (T.gondii) IN ITS NATURAL CYCLE
Cats are the main hosts for the sexual stages of brain worms.
Cats are infested, usually, by ingestion of raw meat, usually rodents, which in turn infested with the parasite via environmental cat feces.
After tissue cysts or oocysts are ingested by the cat, viable organisms ("worms", or worm-like threads) are released and invade epithelial (wall) cells of the small intestine. That is, they are capable of penetrating the walls of the digestive system, and, in fact, capable of migrating throughout the body, especially preferring the brain and retina.
They then sexually form oocysts, which are excreted in the feces for several weeks after infestation.
"The...oocyst takes 1 to 5 days after excretion to ... become infective. Although cats shed oocysts for only 1 to 2 weeks, large numbers may be shed. Oocysts can survive in the environment for several months and are remarkably resistant to disinfectants, freezing, and drying, but are killed by heating to 70 °C for 10 minutes."
http://www.cdc.gov/toxoplasmosis/
After the feces dry, the oocysts are capable of being blown into the ambient air, and potentially ingested by mammals such as rodents, thus completing the life cycle. Ingestion by humans is an accidental byproduct.
Mammalian infestation occurs by:
1. Eating undercooked infected meat.
2. Accidental ingestion of the oocysts from decomposing feces in gardens, or from air-borne dust.
3. Other means, particularly in humans, such as sexual activity or transplants.
4. Not cleaning up cat feces immediately.
"The parasites form tissue cysts, most commonly in skeletal muscle, myocardium, and brain; these cysts may remain throughout the life of the host...Cysts are usually spherical in the brain but more elongated in cardiac and skeletal muscles. They may be found in various sites throughout the body of the host, but are most common in the brain and skeletal and cardiac muscles."
After finding itself in the digestive tract of a mammalian host, the oocytes hatch into "worms" capable of penetrating the intestinal wall and migrating throughout the host body.
