Toxoplasmosis

Toxoplasmosis, one of the most common infectious diseases, is caused by the protozoan Toxoplasma gondii. Depending on their environment and eating habits, up to 70% of people in the United States are infected with T. gondii at any given time. Distributed worldwide, the infection is less common in arid climates (cold or hot) and at high elevations. It usually causes localized infection but may produce significant generalized infection, especially in neonates and in patients who are immunocompromised. Congenital toxoplasmosis, characterized by central nervous system lesions, may result in stillbirth or serious birth defects. For this reason, pregnant women are advised to avoid cleaning cat litter boxes because fecal-oral contamination from infected cats transmits toxoplasmosis.

Causes

T. gondii exists in trophozoite forms in the acute stages of infection and in cystic forms (tissue cysts and oocysts) in the latent stages. In addition to possible fecal-oral transmission from infected cats, ingestion of tissue cysts in raw or uncooked meat (heating, drying, or freezing destroys these cysts) can also transmit toxoplasmosis. However, toxoplasmosis also occurs in vegetarians who aren’t exposed to cats, so other means of transmission may exist. Congenital toxoplasmosis follows transplacental transmission from a chronically infected mother or one who acquired toxoplasmosis shortly before or during pregnancy.

Once infected, the patient may carry the organism for life. Reactivation of the acute infection can occur.

Complications

Toxoplasmosis may cause encephalitis, myocarditis, pneumonitis, hepatitis, or polymycosis. If the disease is acquired in the first trimester of pregnancy, it commonly results in stillbirth. About one-third of infants who survive have congenital toxoplasmosis. The later in pregnancy that maternal infection occurs, the greater the risk will be of congenital infection in the infant. Other defects, which may become apparent months or years later, include strabismus, blindness, epilepsy, and mental retardation. (See Ocular toxoplasmosis.)