Toxoplasmosis is an infection caused by a parasite called toxoplasma gondii. A parasite is any organism that depends on another organism to survive. Many illnesses are caused by parasites. Up to 40% of people in the US have been exposed to the toxoplasma parasite. Common sources of infection are undercooked meat (particularly pork, lamb and venison), cats, birds and other animals. The parasite can also be found in soil contaminated by animal feces. Toxoplasmosis most often affects the brain. Less commonly, toxoplasmosis can affect the eyes, lungs and other parts of the body. A healthy immune system controls the parasite and prevents illness. A damaged immune system is less able to prevent illness. People with less than 100 T4 cells are at the greatest risk for toxoplasmosis.

A test can tell if you have been infected with the toxoplasma parasite. The test looks for antibodies that your immune system makes to stop the parasite from causing illness.

Both people who have been exposed and people who haven't can avoid the toxoplasma parasite by: making sure that any meat is cooked until it is no longer pink inside; wearing gloves while gardening or working with soil or sand; and wearing gloves and a mask when changing cat litter. You can also ask an HIV-negative friend or family member to change the litter. The litter should be changed daily. There is no need to give up a pet cat, but you should avoid adopting or handling stray cats. Pet cats should be fed canned or dried commercial cat foods or well cooked table food, not raw or undercooked meats. Hands and any surfaces that come into contact with raw meat or vegetables should be washed.

The Public Health Service recommends that people who have been exposed to the toxoplasma parasite and who have less than 100 T4 cells take medications to prevent toxoplasmosis. The drug Bactrim can prevent toxoplasmosis. Bactrim is also known as Septra or TMP/SMX and is used to prevent PCP pneumonia. If you can't take Bactrim, the combination of dapsone and pyrimethamine is recommended. Other drugs such as azithromycin (Zithromax), clarithromycin (Biaxin) and atovaquone (Mepron) may also work.

Symptoms of an active toxoplasmosis infection include severe headaches that don't respond to pain killers, weakness on one side of the body, fever, seizures, problems with seeing and difficulty speaking and walking. Nausea, dizziness and vomiting may also occur. Diagnosis of toxoplasmosis can be difficult, because other illnesses such as lymphoma can cause similar markings or lesions on the brain. Brain scans called CTs or MRIs are sometimes used to look for lesions. A test called a PET scan may help tell if brain lesions are caused by lymphoma or toxoplasmosis. Your doctor may start treatment even if it is not certain that you have toxoplasmosis. If you respond to the treatment and the symptoms and lesions get better, toxoplasmosis was the problem.

Treatments for toxoplasmosis usually work very well. The standard treatment is a combination of the drugs pyrimethamine, sulfadiazine and leucovorin. For people that can't take sulfa drugs like Bactrim and sulfadiazine, the combination of pyrimethamine with clindamycin is recommended. Other drugs are being used experimentally, including azithromycin (Zithromax), clarithromycin (Biaxin) and atovaquone (Mepron). Even when you get over toxoplasmosis, you will need to keep taking these treatments to prevent the illness from coming back. It is not yet known whether new combination anti-HIV treatments can improve the immune system enough to stop toxoplasmosis from coming back.

The main side effects from toxoplamosis treatments are allergies to the sulfa drugs: Bactrim/Septra, dapsone and sulfadiazine. Allergic reactions to these drugs can cause severe rash and a life threatening condition known as Stevens-Johnson Syndrome. A process of building up the dose of the sulfa drug slowly, known as desensitization, can sometimes avoid these reactions. Pyrimethamine can cause bone marrow suppression and needs to be given with leucovorin to avoid this side effect. Other side effects of pyrimethamine can be rash, nausea and vomiting. Clindamycin may cause nausea, vomiting, diarrhea and mild rash.

Azithromycin is available through a special program for the treatment of toxoplasmosis if you cannot take other treatments. Doctors can call (800) 742-3029 for more information.

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