toxoplasmosis, infection caused by Toxoplasma gondii, a single-celled parasitic microorganism that can infect most warm-blooded animals but reproduces only in animals of the cat family, who shed the parasite in their feces. In most healthy persons, the immune system can prevent the parasite from causing illness, and there are no symptoms; in some cases, there are flulike symptoms. Despite a lack of symptoms and a healthy immune system, T. gondii can survive for a long time in a person or other host by forming cysts, usually in skeletal or heart muscle, the brain, or the eyes.

Infection is more severe in persons with weakened immune systems, including formerly healthy persons in whom the parasite is reactivated, and in children whose mothers become infected just before or during pregnancy. In such cases, the brain, eyes, and other organs can be harmed by the parasite. Symptoms may include headache, confusion, poor coordination, seizures, and lung problems, and blurred or reduced vision, pain (which may occur in association with bright light), redness of the eye, and tearing if an eye is involved. Infections during pregnancy can cause a miscarriage or stillbirth. Infected newborns do not usually show symptoms; seizures, jaundice, eye infections, hearing loss, mental disability, or other symptoms typically develop later, sometimes in the child's teens or after.

Toxoplasmosis is often treated with pyrimethamine and sulfadiazine in conjunction in many cases with folinic acid. Persons with weakened immune systems may be given pyrimethamine and clindamycin instead; pregnant women infected before the 16th week are given spyramycin. Because infection may result from contact with cat feces that is a day old or older, contact with contaminated soil or sand outdoors, eating meat from infected animals, eating unwashed or unpeeled raw contaminated produce, eating raw contaminated shellfish, and drinking contaminated water, such precautions as cleaning cat litter promptly, using gardening gloves, properly preparing and cooking food, and drinking treated water can help prevent infection.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2022, Columbia University Press. All rights reserved.

See more Encyclopedia articles on: Pathology