Causes

Toxoplasma gondii (T. gondii) is a single-celled parasitic organism that can infect most animals and birds. Because T. gondii infectious organisms are excreted only in cat feces, wild and domestic cats are the parasite's ultimate host.

Although you can't "catch" toxoplasmosis from an infected child or adult, you can become infected if you:

• Come into contact with cat feces that contain the parasite. You may accidentally ingest the parasites if you touch your mouth after gardening, cleaning a litter box or touching anything that has come in contact with infected cat feces. Cats who hunt or who are fed raw meat are most likely to harbor T. gondii.
• Eat or drink contaminated food or water. Lamb, pork and venison are especially likely to be infected with T. gondii. Occasionally, unpasteurized dairy products also may contain the parasite. Water contaminated with T. gondii isn't common in the United States.
• Use contaminated knives, cutting boards or other utensils. Kitchen utensils that come into contact with raw meat can harbor the parasites unless the utensils are washed thoroughly in hot, soapy water.
• Eat unwashed fruits and vegetables. The surface of fruits and vegetables may contain the parasite. To be safe, thoroughly wash and peel all produce, especially any you eat raw.
• Receive an infected organ transplant or transfused blood. In rare cases, toxoplasmosis can be transmitted through an organ transplant or blood transfusion.

When a person becomes infected with T. gondii, the parasite forms cysts that can affect almost any part of the body — often your brain and muscle tissue of different organs, including the heart.

If you're generally healthy, your immune system keeps the parasites in check. They remain in your body in an inactive state, providing you with lifelong immunity so that you can't become infected with the parasite again. But if your immune system is weakened by disease or certain medications, the infection can be reactivated, leading to serious complications.