Toxoplasmosis is a parasitic infection caused by a protozoan known as Toxoplasma gondii. Humans most often become infected with this organism by consuming undercooked meat—especially lamb and pork—or eating unwashed fruits and vegetables. Raw goat milk has been known to carry the parasite. Animals are not immune to this illness. Cats—domestic and wild—are often carriers. A person who comes in contact with cat feces, such as when changing a litter box, is especially prone to the disease. Other less common causes include blood transfusions and organ transplants.

The three forms of T. gondii, the microorganism that causes toxoplasmosis, are

• tachyzoites, which reproduce rapidly,
• bradyzoites, which reproduce more slowly and are contained in tissue cysts, and
• sporozoites, which are contained in oocysts.

A healthy person who becomes infected with this parasite experiences few or no symptoms. An estimated half of Americans and one-third of Canadians carry antibodies from past exposure without being aware. However, people who have a weakened immune system, such as older individuals and AIDS patients, are at risk for severe complications.

Pregnant women who contract toxoplasmosis put their unborn child at great risk. The effect of T. gondii on a fetus is severe. Women who become infected in the late months of pregnancy are likely to pass the parasite to their unborn child through the placenta. If the mother was infected at the time of conception or if the fetus is infected during the first trimester of pregnancy, a miscarriage is likely. Infants born with toxoplasmosis usually have severe eye infections, a swollen liver or spleen, jaundice, or pneumonia. The mortality rate of babies born with toxoplasmosis is high. If the infected baby survives, it is likely that the child will be visually impaired, have fluid in the brain, and suffer from learning disabilities or mental retardation.

Symptoms
Often, the disease has no signs or symptoms, which makes it even more dangerous. In the cases that have been reported, the first visible signs are painless swelling of lymph nodes and flulike symptoms such as headache, fever, fatigue, muscle and joint aches, and rashes. Rare but deadly symptoms of toxoplasmosis are inflammation of the brain (meningoencephalitis), lungs (pneumonitis), heart muscle (myocarditis), and liver (hepatitis).

After a person is infected, cysts containing bradyzoites form. The cysts are found mainly in the brain, eye, heart muscle, and skeletal muscle. When the cysts burst, the effects are serious and include blindness, brain damage, and other severe illness. Any organ in the body can be affected. Numerous cases of toxoplasmosis have been reported throughout the world, but the disease is more common in warmer climates.

Prevention
To prevent exposure to the disease, cook all meat at a temperature of at least 160 °F, and wear gloves when handling raw meat. Wash all fruits and vegetables well before eating. Avoid contact with kitty litter, and make sure your cats don’t eat birds or rodents because they may be infected with T. gondii. It is also important not to give your cat raw meat scraps.

An aging and weakened immune system in AIDS patients and older people is no match for this powerful and deadly parasite. An already depleted immune system causes toxoplasmosis patients to endure brutal symptoms ranging from severe headache, stiff neck, fever, delirium, and muscle weakness to clumsiness, speech impairment, and seizures.

Treatment
Individuals diagnosed with a simple case of toxoplasmosis usually do not require treatment. The body fights the flulike infection, and recovery takes only a few weeks. High-risk groups such as pregnant women, AIDS patients, older people, and transplant patients require a combination of antibiotics to limit multiplication of the parasite. Medications that are frequently prescribed include a combination of pyrimethamine and sulfadiazine or a combination of pyrimethamine and clindamycin. For AIDS patients, atovaquone is widely used, and it appears to completely cure toxoplasmosis. Atovaquone also eliminates the need to continue any other antibiotic. A simple blood and tissue test is effective in detecting T. gondii. Other treatment options are currently under development.

For further information

• Congenital Toxoplasmosis, www.trojovsky.net/toxo
• CDC, Division of Parasitic Diseases, Toxoplasmosis, www.cdc.gov/ncidod/dpd/parasites/toxoplasmosis
• Human Toxoplasmosis, Ho-Yen, D. O., Joss, A. W., Eds.; Oxford Medical: New York, 1992.