Toxoplasmosis

Toxoplasmosis (tox-o-plaz-MO-sis), often called toxo, is a parasitic infection that usually causes no symptoms in healthy people, but it can be serious in people with weak immune systems and in unborn babies.

What Is Toxoplasmosis?

The parasite Toxoplasma gondii, the organism behind toxoplasmosis, is found in soil and can infect humans and many species of animals. It is often found in cats, and is passed in cat feces (FEE-seez, or bowel movements). Touching dirty litter from a cat's litter box is one common way that people contract the parasite. Eating undercooked meat or accidentally eating contaminated soil are other ways that people become infected.

Many people who have toxoplasmosis have no symptoms or symptoms that are very mild. However, women who become infected when they are pregnant can pass the organism to the fetus^*. In an unborn child, the parasite can cause congenital^* toxoplasmosis, a condition that can range from mild to severe and may involve developmental problems and mental retardation, seizures^*, and vision problems. Toxoplasmosis also can take a heavy toll on people with weakened immune systems, such as those with AIDS^* or cancer, or those who have had an organ or bone marrow^* transplant. Toxoplasmosis may affect the brain in these people.

How Common Is Toxoplasmosis?

The U.S. Centers for Disease Control and Prevention estimates that as many as 60 million people in the United States have been infected with T gondii, but cases of actual disease are much less common. Most people who carry the parasite have no symptoms of illness.

Is Toxoplasmosis Contagious?

Pregnant women who are infected during pregnancy can pass the organism to the unborn child, but this is the only way that it spreads from person to person. Many people contract toxoplasmosis from eating raw or undercooked meat containing the parasite's cysts^*, especially pork and lamb. Others unknowingly ingest the parasite's eggs after touching cat feces, soil, or anything that has come into contact with cat feces. The eggs can stick to a person's hands and may eventually end up in the mouth, where they can be swallowed.

A microscopic view of the Toxoplasma gondii parasite. More than 60 million Americans have been infected with this single-celled parasite, though usually only people with weakened immune systems become ill.

©Arthur M. Sieglman

What Happens to People with Toxoplasmosis?

Most people with the infection have no symptoms. When symptoms do occur, they may include swollen lymph nodes^*, muscle aches, headache, and sore throat. For people with weakened immune systems (especially those with AIDS), toxoplasmosis can cause severe infection of the brain or, less commonly, the lungs or heart. As a result, symptoms are worse, and they may include fever, headache, confusion, seizures, blurred vision from inflammation of the retina^*, psychosis (sye-KO-sis, form of mental illness in which an individual becomes disconnected from reality), and problems with speech or movement. Severe disease can be fatal.

In some cases, infection in a pregnant woman induces a miscarriage^*. Congenital infection in newborns may be marked by small body and head size, jaundice^*, rash, fever, anemia^*, inflamed retinas, and an enlarged spleen and liver. These children may develop blindness, mental retardation, learning disabilities, and other problems with the central nervous system (the part of the nervous system that includes the brain and spinal cord), such as seizures and difficulty controlling movements. Sometimes the developmental disabilities are present from birth and sometimes they do not appear for many months or years.

How Do Doctors Diagnose Toxoplasmosis?

If a doctor suspects toxoplasmosis, he or she will draw a blood sample and test it for evidence of the parasite. An eye doctor may use a special lamp called a slit lamp to check the eyes for abnormalities of the retinas. People with weakened immune systems who are more likely to develop a severe infection might have magnetic resonance imaging^* (MRI), a computerized tomography^* (CT) scan of the head, or rarely, a brain biopsy (removing a small sample of brain tissue to examine) to look for signs of damage caused by the parasite. Infants with congenital toxoplasmosis also will need a CT scan of the head and thorough examination of other areas of the body possibly affected by the parasite.

What is the Treatment for Toxoplasmosis?

People who have toxoplasmosis but are otherwise healthy do not need any treatment. However, people with weak immune systems, pregnant women, and newborns with the congenital infection are treated with medication. Patients with AIDS often continue taking the medicine even after the infection clears up to keep it from returning.

Healthy people usually have symptoms for only a few days, if at all. In newborns and patients with unhealthy immune systems, the illness can last for weeks or months and cause permanent disability.

Can Toxoplasmosis Be Prevented?

Pregnant women and people whose immune systems are weak can take steps to avoid infection with T. gondii. First, they can be tested for the parasite. If they test positive, they will likely be started on medication for the infection, even if they do not have any symptoms. If they test negative, they can follow some simple measures to keep from becoming infected in the future, such as:

• wearing gloves when gardening and handling soil to prevent infection from parasites in the dirt
• wearing gloves when cooking or having someone who is healthy and not pregnant handle raw meat
• cooking all meat thoroughly, until the juices run clear and it is no longer pink inside
• washing all utensils and cutting boards that have come into contact with raw meat in hot water and soap
• washing hands frequently, particularly after outdoor activities, after preparing food, and before eating
• keeping family cats inside and feeding them only dry or canned cat food, because cats can pick up the parasite from eating raw meat
• having someone who is healthy and not pregnant change the cat's litter box every day
• not touching strange or stray cats or letting any cat into the home that might have lived outside or eaten raw meat

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