Toxoplasmosis is a parasitic infection that infects a large proportion of the world's population, but rarely causes disease. Certain people, however, are at high risk of severe or life-threatening disease from this parasite. They include infants who are infected at birth, people with AIDS, people with cancer, and people who have had bone marrow or organ transplantation.
Toxoplasmosis is an infection caused by Toxoplasma gondii, a single-celled parasite that spends most of its life cycle inside cats. Because an infected cat can pass millions of Toxoplasma parasites daily in its feces, toxoplasmosis can spread easily to almost any other animal that shares the environment with cats. In humans, Toxoplasma parasites usually enter the body by being swallowed. This can happen when people touch their mouth with soiled hands, especially after changing cat litter, or if they eat pork, lamb or venison that has not been cooked thoroughly.
The Toxoplasma parasites multiply within cells that line the human digestive tract. Toxoplasma parasites can spread to almost any organ in the body, including the brain, skeletal muscles, heart muscle, eyes, lungs and lymph nodes. In healthy people, the body's immune system eventually stops the spread of Toxoplasma parasites, although some remaining parasites can lie dormant indefinitely in the brain or retina.
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