Toxoplasmosis
Toxoplasmosis is infection caused by Toxoplasma gondii, a single-celled parasite.
Toxoplasma is present worldwide and infects people and a large number of animals and birds. Many people in the United States have been infected with Toxoplasma, although few ever develop symptoms. Severe illness generally develops only in fetuses and people with a weakened immune system.
Although the parasite can grow in the tissues of many animals, it produces eggs (oocysts) only in cells lining the intestine of cats. Eggs are shed in a cat's stool and can survive for up to 18 months in the soil.
People who touch soil contaminated with Toxoplasma eggs may acquire the infection from direct hand-to-mouth contact or by contaminated food, which is then eaten. Occasionally animals such as pigs acquire toxoplasmosis from contaminated soil. People can become infected by eating raw or undercooked meat from infected animals. Both freezing and thoroughly cooking meat destroy Toxoplasma.
A woman who acquires the infection while pregnant can transfer Toxoplasma to her fetus through the placenta. The result may be a miscarriage, stillbirth, or a baby born with congenital toxoplasmosis (see Section 23, Chapter 264). A woman who was infected before the pregnancy will not pass the parasite on to the fetus.
People with a weakened immune system, primarily those with AIDS or cancer, or those who have received an organ transplant and drugs to suppress rejection, are especially at risk of toxoplasmosis. Symptoms usually develop in these people because of reactivation of a previously acquired Toxoplasma infection. The infection usually occurs in the brain, but it may affect the eye or be spread (disseminated) throughout the body. In these people, toxoplasmosis is very serious and nearly always fatal when untreated.
Symptoms and Diagnosis
Children born with congenital toxoplasmosis may be severely ill and die shortly after birth, or they may have no symptoms until months or years later. Some never develop illness. Typical symptoms in newborns can include inflammation of the eyes (chorioretinitis), which can result in blindness, enlargement of the liver and spleen, jaundice, easy bruising, seizures, a large or small head, and mental retardation.
Toxoplasmosis acquired after birth in otherwise healthy people seldom causes symptoms. When symptoms occur, they are usually mild and include painless, swollen lymph nodes; intermittent low fevers; and a vague ill feeling. Sometimes people develop only chorioretinitis, with blurred vision, eye pain, and sensitivity to light.
Symptoms of toxoplasmosis in people with a weakened immune system depend on the site of infection. Toxoplasmosis of the brain (encephalitis) produces symptoms such as weakness on one side of the body, trouble speaking, headache, confusion, and seizures. Acute disseminated toxoplasmosis can cause a rash, high fever, chills, trouble breathing, and fatigue. In some people, infection causes inflammation of the brain and its lining (meningoencephalitis), liver (hepatitis), lungs (pneumonitis), or heart (myocarditis).
The diagnosis of toxoplasmosis is usually based on a blood test that reveals antibodies against the parasite. However, if the person's immune system is impaired by AIDS, the blood test may be falsely negative. A doctor may instead depend on computed tomography (CT) and magnetic resonance imaging (MRI) of the brain. Less commonly, a piece of infected tissue is removed and examined under a microscope (biopsy) to make the diagnosis.
Treatment and Prognosis
Infected adults without symptoms and with a healthy immune system do not require treatment. Those with symptoms are treated with sulfadiazine plus pyrimethamine, with the addition of leucovorin to protect the bone marrow from the toxic effects of pyrimethamine. Alternatively, people with chorioretinitis can be given clindamycin, along with prednisone or another corticosteroid to reduce inflammation.
Toxoplasmosis in people with AIDS tends to recur, so drugs are often given indefinitely. To prevent toxoplasmosis, some people with AIDS are placed on preventive treatment with trimethoprim-sulfamethoxazole, which also helps prevent Pneumocystis carinii infection.
Women who are known to have acquired toxoplasmosis during pregnancy may be treated with spiramycin to prevent transmission to the fetus. Pregnant women should avoid cleaning cat litter boxes or should wear gloves when doing so. Meat should be cooked thoroughly before ingestion.
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