- Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii.
- Humans can contract toxoplasmosis by swallowing organisms from contaminated food or cat faeces.
- Most toxoplasmosis in HIV-infected persons is the result of reactivation of an old infection, which usually involves the brain.
- Symptoms of toxoplasmosis may include fever, headache, confusion, sleepiness, weakness or numbness in one part of the body, seizures and vision problems.
- Toxoplasmosis is most commonly treated with the drug co-trimoxazole.
What is toxoplasmosis and what causes it?
Toxoplasmosis (also known as "toxo"), a common infection throughout the world, is caused by the parasite Toxoplasma gondii. In people with normal immune function, Toxoplasma, organisms remain in the body tissues as cysts that do not cause disease. In persons with impaired immunity, however, Toxoplasma can multiply and cause disease in the brain and sometimes other body organs.
Humans can contract toxoplasmosis in the following ways:
- Through contact with infected cat stool. Domestic cats can transmit Toxoplasma by passing an infectious form of the parasite, oocysts, in their faeces. Toxoplasma is only present in the faeces for a few weeks after the cat is first infected. Like humans, cats rarely have symptoms when first infected, and there are no good tests available to determine if your cat is infected.
- By swallowing organisms in contaminated food or picked up on dirty hands, eating undercooked meat or eggs, or drinking unpasteurised milk containing tissue cysts from infected animals.
- Women who become infected with Toxoplasma during pregnancy sometimes transmit it to their unborn babies.
How can toxoplasmosis affect people with HIV/Aids?
Toxoplasma is common in the environment, so many HIV-infected people have the inactive form of the parasite (cysts) in their bodies, usually in brain or muscle tissue. These infections stay inactive as long as the infected person’s immune system is strong. However, in advanced HIV disease (CD4 cell count less than 100/ul), the immune system may not be able to control the infection and illness results. Up to half of all persons with Aids who have toxoplasmosis infection and a CD4 count under 100 get toxo-related illness. Most toxoplasmosis in HIV-infected individuals is the result of reactivation of an old infection, which usually involves the brain.
Symptoms and signs of toxoplasmosis
Symptoms of toxoplasma infection of the brain may include headache, fever, confusion, sleepiness, weakness or numbness in part of the body, seizures, poor co-ordination and changes in vision. These symptoms can progress to coma and death unless the infection is diagnosed and treated in time.
Toxoplasma infection affecting parts of the body other than the brain is uncommon. In such cases, symptoms depend on the organ affected. Infection of the eye is seen in people with Aids, and such a person will notice that their vision is worsening in one eye.
How is toxoplasmosis diagnosed?
If you have symptoms that suggest toxoplasmosis, and your CD4 count is below 100/ul, your doctor will likely order a CT or MRI scan of the brain. If the scan shows abnormalities suggestive of toxoplasmosis, you will be prescribed medications to treat the condition. If your symptoms do not start to resolve within a few weeks, another disease may be causing the symptoms, and further diagnostic tests may be necessary.
If you do not have symptoms of toxoplasmosis, but wish to know if you are carrying inactive toxoplasma cysts, a blood test, the Toxoplasma antibody test, can determine this. A positive test result means you have antibodies to Toxoplasma in your blood, and that you were infected by the parasite in the past. This does not necessarily mean you have active infection, but it does mean you may be at risk for toxoplasmosis in the future. A negative test result indicates that you are at very low risk of developing toxoplasmosis
How is toxoplasmosis treated?
Toxoplasmosis is most commonly treated with the drug co-trimoxazole (trimethoprim and sulfamethoxazole together). High-dose therapy is continued for four to six weeks, followed by lower dose maintenance therapy for at least 12 weeks. Maintenance therapy can be discontinued in patients who have completed the course of initial treatment, are free of symptoms, and whose CD4 cell count rises to 200/ul for six months on antiretroviral therapy.
Sulfamethoxazole may sometimes cause allergic reactions, including rash, and nausea, vomiting and diarrhoea. Some reactions can be controlled by taking an anti-histamine (anti-allergy drug). Trimethoprim can cause low blood counts in some people. To counter the possible effects of trimethoprim on the bone marrow, folate supplements can be taken. If you cannot tolerate co-trimoxazole, clindamycin and pyrimethamine may be prescribed instead. Other drugs sometimes used to treat toxoplasmosis include clarithromycin, azithromycin, dapsone and atovaquone. These may be considered if the standard treatment is ineffective or causes unacceptable side-effects.
The combination drug trimethoprim-sulfamethoxazole (TMP-SMX, Bactrim, Septra) that is given as a preventive treatment for Pneumocystis cariniii pneumonia (PCP) is also effective in preventing toxoplasmosis in people who are positive for toxoplasma antibody and have a CD4 count less than 100/mm3. Some people develop allergic reactions to TMP-SMX, including fever, rash and digestive tract problems. As an alternative, the drug dapsone can be used.
How can I help prevent toxoplasmosis?
Get tested for Toxoplasmosis, and if you have a negative antibody test, you can help avoid Toxoplasma infection by taking certain precautions, such as:
- Don’t eat undercooked or raw meat or eggs, and don’t drink unpasteurised milk.
- Wash your hands before eating or handling food, as well as after touching raw meat and outdoor activities such as gardening.
- Wash fruits and vegetables well before eating them raw.
- You do not need to give up your cat if you own one, but should take the following precautions:
- Make sure the litter tray is cleaned regularly, and keep it outside or away from the main living areas. Ask someone who is not infected with HIV and is not pregnant to change the litter box daily. If you must clean the box yourself, wear gloves and wash your hands well with soap and water afterwards.
- Keep your cat indoors to prevent it from hunting.
- Feed your cat only cat food or cook all meat thoroughly before giving it to your cat. Do not give your cat raw or undercooked meat.
- If you get a cat, choose one that is healthy and at least one year old. Avoid stray cats and kittens that are more likely to be infected with Toxoplasmosis.