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Causes
By Mayo Clinic staff
Toxoplasma gondii (T. gondii) is a single-celled parasitic organism that can infect most animals and birds. But because it reproduces sexually only in cats, wild and domestic felines are the parasite's ultimate host. T. gondii's complex life cycle begins when a cat eats infected prey, usually a mouse or bird.
Cats can also become infected if they are fed raw, contaminated meat or eat infected soil. Once ingested, T. gondii burrows into the walls of the cat's small intestine, forming early-stage cells called oocysts that the cat eliminates in its feces, usually for a period of two to three weeks. A single stool may contain millions of oocysts. Most healthy cats won't shed oocysts after this initial acute stage.
Within a few days, the oocysts develop into mature, highly infectious cells that under certain conditions can survive in the soil for months. If they're ingested by another animal, they multiply rapidly inside the host, eventually forming inactive cysts that lodge mainly in the brain or muscles. Although the new host animal usually remains symptom-free and won't excrete oocysts, it can still transmit the parasite to any predator that eats it.
What happens in humans
In many respects, the pattern is similar in humans. After you're infected with T. gondii, the parasite forms cysts that can affect almost any part of the body, but often affects your brain and muscles, including the heart.
If you're generally healthy, your immune system keeps the parasites at bay, and they remain in your body in an inactive state for life. This provides immunity so that you can't become infected with the parasite again. But if your resistance is weakened by disease or certain medications, the infection can be reactivated, leading to serious complications.
Although you can't "catch" toxoplasmosis from an infected child or adult, you can become infected if you come in 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's come in contact with infected cat feces. Cats who hunt or who are fed raw meat are most likely to harbor T. gondii.
- Ingesting 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 cysts. Additionally, while not common in the United States, water can be contaminated with T. gondii, but this is not common in the United States.
- Contaminated knives, cutting boards or other utensils. Kitchen utensils that come in contact with raw meat can harbor the parasites unless the utensils are washed thoroughly in plenty of hot, soapy water.
- Contaminated, unwashed fruits and vegetables. The surface of fruits and vegetables may contain traces of the parasite. To be safe, thoroughly wash all produce, especially any you eat raw.
- An infected organ transplant or transfused blood. In rare cases, toxoplasmosis can be transmitted through an organ transplant or blood transfusion.
- Toxoplasmosis fact sheet. Centers for Disease Control and Prevention. http://www.cdc.gov/toxoplasmosis/factsheet.html. Accessed May 5, 2009.
- Martin-Rabada P, et al. Blood and tissue protozoa. In: Cohen J, et al. Infectious Diseases. 2nd ed. New York, N.Y.: Mosby; 2004. http://www.mdconsult.com/das/book/body/135708454-2/0/1209/737.html?tocnode=49359306&fromURL=737.html#4-u1.0-B0-323-02407-6..50247-6--cesec17_8111. Accessed May 4, 2009.
- Kasper LH. Toxoplasma infections. In: Fauci AS, et al. Harrison's Principles of Internal Medicine. 17th ed. New York, N.Y.: McGraw-Hill Medical; 2008. http://www.accessmedicine.com/content.aspx?aid=2896423. Accessed May 4, 2009.
- McLeod R, et al. Toxoplasmosis (toxoplasma gondii). In: Kleigman RM, et al. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa.: Saunders Elsevier; 2008. http://www.mdconsult.com/das/book/body/135783748-2/0/1608/732.html?tocnode=54480801&fromURL=732.html#4-u1.0-B978-1-4160-2450-7..50289-9_6064. Accessed May 4, 2009.
- Toxoplasmosis. March of Dimes. http://www.marchofdimes.com/professionals/14332_1228.asp. Accessed May 6, 2009.
- Centers for Disease Control and Prevention, et al. Preventing congenital toxoplasmosis. MMWR Recommendations and Reports. 2000;49:57. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr4902a5.htm. Accessed May 8, 2009.
- You can prevent toxo. Centers for Disease Control and Prevention. http://www.cdc.gov/hiv/resources/brochures/toxo.htm. Accessed May 5, 2009.
- Montoya JG, et al. Diagnosis and management of toxoplasmosis. Clinics in Perinatology. 2005;32:705.
