Toxoplasmosis

Toxoplasmosis is caused by the zoonotic parasite Toxoplasma gondii. It can spread to humans by eating undercooked meat that contains tissue cysts with bradyzoites.

It can also be transmitted through oocysts shed by definitive hosts such as cats.

These oocysts sporulate in the environment, contaminate the surroundings, and can infect humans when they are ingested.

After ingestion, gastric juices break down the outer cyst wall in the digestive tract. This releases sporozoites that enter the gut epithelium.

The sporozoites turn into rapidly dividing tachyzoites, which invade immune cells to spread throughout the body.

The immune cells carry tachyzoites across the blood-brain barrier. This triggers the production of interferon-gamma, which limits the growth and spread of tachyzoites.

The tachyzoites then change into slow-dividing bradyzoites.

In healthy humans, bradyzoites stay in tissues, divide slowly, and form cysts without causing disease.

If the host immune system is suppressed, these bradyzoites can rapidly turn back into tachyzoites, causing encephalitis, which is inflammation of the brain tissue.