Toxoplasmosis

Toxoplasmosis, a parasitic disease, occurs worldwide in nearly all warmblooded animals, including humans. It is caused by a single-celled (protozoan) parasite called Toxoplasma gondii, an organism usually contracted by eating undercooked meat from infected animals. Cats are often wrongly blamed as the major source of infection. Because the parasite produces eggs only in cats, they are the definitive .T gondii host. However, humans can acquire toxoplasmosis from them only by direct contact with cat feces containing T. gondii eggs. A cat may eat infected mice or raw meat containing cysts of T. gondii. The protozoan then reproduces sexually in the cat's small intestine, and one to four weeks later, its eggs are excreted.

When a human or another animal ingests the T. gondii organism or its eggs, the parasite makes its way to various tissues --usually the muscles, but also the brain, eyes, heart, and lungs -- where it forms cysts. The body makes antibodies against the organism, though the T. gondii in the cysts remain viable for the lifetime of their host.

The vast majority of people are never aware that they have been infected. When symptoms do develop, they generally last for a few weeks and may include malaise, muscle aches, sore throat, and perhaps a fever and swollen lymph nodes. In a few cases, cysts form in the eyes, causing inflammation and sometimes vision problems. Otherwise, toxoplasmosis usually is not a serious disease, with two major exceptions:

1. Fulminating, disseminated infection, which can produce encephalitis, hepatitis, pneumonia, and inflammation of the heart. This form occurs mostly in AIDS patients and others who have weakened immune systems.
2. Congenital toxoplasmosis, in which a pregnant woman passes the infection to her fetus. Babies who contract toxoplasmosis may suffer such consequences as mental retardation, seizures, deafness, and blindness.

Diagnostic Studies and Procedures

In otherwise healthy people, a blood test shows a characteristic rise in toxoplasmosis antibodies. Some doctors recommend routine testing of newly pregnant women for the antibodies. An infection acquired during, but not before, pregnancy carries a high risk of fetal infection. If congenital toxoplasmosis is suspected in a newborn, confirmation is based on blood tests, analysis of cerebrospinal fluid, and inspection of the placenta for presence of T. gondii. The eyes may be examined for cysts and other abnormalities.

Antibody tests are of little value in detecting toxoplasmosis in AIDS patients and others with compromised immune systems, in these cases, diagnosis is based on symptoms and perhaps a culture.

Medical Treatments

Most cases are asymptomatic and self-limited, requiring no treatment. An acute infection, especially in an AIDS patient, is treated with oral sulfa drugs and an anti-parasitic drug. One such combination is sulfadoxine plus pyrimethamine (Fansidar). Patients taking this should call their doctor immediately if they develop a skin rash, a sign of a potentially life-threatening adverse reaction.

Because of the high rate of relapses among AIDS patients, treatment is continued indefinitely. All patients receiving pyrimethamine need periodic blood tests to monitor for toxic effects and suppression of bone marrow function.

Treatment during pregnancy is somewhat problematic. Studies show that treating a woman who has an acute infection reduces the incidence and severity of congenital toxoplasmosis, but the drugs used, especially pyrimethamine, are potentially hazardous to the fetus. In each case, a doctor considers the stage of pregnancy. Pyrimethamine and sulfa drugs are relatively safe after the first trimester and may prevent or reduce the severity of the disease. Spiramycin, a drug used in Europe and available from the Food and Drug Administration for special use in the United States, is safer during the first trimester.

Infants who have congenital toxoplasmosis usually are treated with pyrimethamine plus a steroid.

Chronic toxoplasmosis affecting the eyes may be treated with clindamycin, an antibiotic. In some cases, corticosteroids may reduce inflammation.

Alternative Therapies

Alternative therapies are not useful in treating toxoplasmosis.

Self-Treatment

Prevention is the best approach to self-treatment The following are some practical guidelines:

• Make sure that all meat is cooked until well done, or to an internal temperature of 151° F (71° C).
• Wash your hands and utensils thoroughly after handling raw meat.
• To protect pet cats, feed them only commercially prepared food and prevent them from hunting in the wild.
• Use dry cat litter and dispose of the feces every day. Be sure to wash your hands afterwards. (To be extra safe, a pregnant woman or AIDS patient can ask someone else to change the cat's litter box.) The T. gondii eggs are not infective until 24 to 48 hours after passage. After that time, they remain infective for a year or more.
• Wear gloves when gardening or handling soil that may contain cat waste. If children play in a backyard sandbox, keep it covered when not in use.

Other Causes of Toxoplasmosis Symptoms

Mononucleosis, flu, and other viral infections can produce symptoms similar to those of toxoplasmosis.