Toxoplasmosis

What is a parasite?

A parasite is a general term for any living thing (organism) that lives in, or on, another living organism. It may feed off its host, or obtain shelter using its host. However, it contributes nothing to its host's well-being or welfare. Human parasites include fungi, protozoa and worms.

What is toxoplasmosis?

Toxoplasmosis is the term used for infection with toxoplasma. Toxoplasma is a living thing (organism) and, as it lives within another organism, it is known as a parasite). Most people have no ill effects but occasional complications include infection of the eyes, brain and other organs. It can also pass from a pregnant woman through the placenta. The placenta is the organ that provides nourishment and oxygen to the baby in the womb (uterus).

Toxoplasma is a protozoan parasite. A protozoan is a microscopic, single-celled organism. The main source of toxoplasma infection is cat droppings. Food contaminated with cat droppings can infect cattle, sheep, pigs, rodents and birds. The species which commonly causes illness in humans is called Toxoplasma gondii.

How do you catch toxoplasmosis?

Whilst many animals can become infected with toxoplasma, cats are the main host. When a cat becomes infected, the toxoplasma invades the gut lining and starts to reproduce immature forms called oocysts. These pass out in the cat's stools (faeces). You can then become infected by coming into contact with contaminated soil, water or food. You can, for example, become infected by:

• Eating undercooked or raw meat - particularly pork or lamb.

• Eating fruit or vegetables that have not been washed properly.

• Handling contaminated soil whilst gardening or contaminated cat litter.

Expectant mothers can pass toxoplasma to their unborn baby through the placenta (the organ providing nourishment and oxygen to the baby). Rarely, toxoplasma can be passed from an infected organ donor to the person receiving the organ.

How common is toxoplasmosis and who catches it?

About 350 cases of toxoplasma infection are diagnosed ih the UK every year. The actual number of infected people is likely to be higher, as toxoplasma often causes no symptoms and the person may be unaware that they have caught it. It is more common in hot damp countries where conditions are more favourable for the survival of the oocysts.

Anyone can become infected with toxoplasma - adults and children, men and women.

If your immune system is not working properly for some reason - for example, you are undergoing treatment for cancer or you have HIV infection - you are more likely to have serious infection.

What are the symptoms of toxoplasmosis?

If your immune system is working properly, the chances are that you will develop no symptoms at all. About one in ten people notice swollen glands. These are usually at the sides of the neck or nape of the neck (the occipital region). The swellings usually disappear in about six weeks but can last longer. Rarely, you can develop a more widespread infection involving the heart, lungs and other organs of the body.

If your immune system is not working properly (for example, because you are taking anti-cancer medicine or have HIV infection) you can become very ill. If the infection involves your brain you may become confused, have fits, develop paralysis down one side of your body or have speech problems. Your eyes can become infected (see below) and the infection can spread to your lungs and other organs of your body.

If you become infected in pregnancy you may notice no symptoms or you may feel under the weather and develop swollen glands or eye problems. If congenital infection occurs (that is, if the infection is passed to the baby) the results can be severe. Such complications are more likely if infection happens in the first ten weeks of pregnancy. Miscarriage can occur or deformities may be picked up on an ultrasound scan. Babies can be born with brain problems, eye conditions, epilepsy, growth delay or blood disorders. The baby may appear normal at birth and problems may only become obvious later on.

Toxoplasma can infect your eyes whether or not your immune system is working properly. It can also occur in congenitally infected babies. The most common eye problem caused by toxoplasmosis is called chorioretinitis. This infection involves the eye's middle layer (the choroid) and its inner lining (the retina).

Eye cross-section

You may notice problems with your eyesight and floaters (specks appearing to float across your field of vision). Usually, only one eye is affected. You may have mild pain in the eye but most people do not have any discomfort.

How is toxoplasmosis diagnosed?

If you are suspected of having toxoplasmosis, the first test you are likely to be offered is a blood test. This will show that the levels of proteins (immunoglobulins) produced by the immune system to fight infection will be high. There are various types of immunoglobulins. IgG level rises in the first 1-2 weeks of infection and stays positive for life. IgM levels rise in the first week and drop to normal after a few weeks, so this test is useful to detect recent infection. IgA levels are sometimes tested in babies.

Other body fluids are sometimes tested - for example, the amniotic fluid surrounding the baby in the womb (uterus).

A small piece of tissue may be removed surgically from the body. This is called a biopsy. It is tested when there continue to be doubts about the diagnosis.

You may need pictures of the brain, using magnetic resonance imaging (MRI) or computed tomography (CT) scanning if brain infection is suspected.

Unborn babies may need an ultrasound scan if it is suspected that infection has been passed from the mother.

How is toxoplasmosis treated?

If your immune system is working properly the chances are that you will not need treatment. If your symptoms are severe or slow to clear up you may, however, need some antibiotic medication for 4-6 weeks. The combination usually used is pyrimethamine and sulfadiazine. These medicines can harm the bone marrow when given alone so folinic acid is often added to reduce this risk.

This combination may also be used if your immune system is not working properly. However, you may also be offered alternatives such as trimethoprim+sulfamethoxazole (co-trimoxazole), clindamycin or atovaquone, depending on your individual circumstances. After a 4- to 6-week course you will probably need to take a low dose of medicine for the rest of your life, unless the problem affecting your immune system is only temporary.

If you become infected whilst you are pregnant you will be offered antibiotics. However, it is not certain how much good this does in terms of preventing infection of the baby. Many types of medicine are available. The choice depends on several factors, such as whether or not your immune system is working properly and whether the baby is already infected. Spiramycin appears to be the best option for protecting babies who have not yet been infected. If the baby is severely infected, you may be offered an abortion.

If you develop a toxoplasma infection of the eye this usually needs no treatment, providing your immune system is working properly. However, you may need treatment if the infection is severe or likely to cause scarring that affects your vision. The usual treatment is antibiotic tablets, steroid eye drops and, in severe cases, steroid tablets.

If your immune system is not working properly you will almost certainly be offered antibiotics. If you are pregnant, spiromycin is the best option.

• If your nervous system is infected you may have fits, deafness or other nervous system problems.

• If you develop an eye infection this can sometimes cause problems with your eyesight and in rare cases lead to severe sight impairment.

• If your immune system is not working properly the infection can spread to your heart, lungs and other organs of your body.

Does toxoplasmosis get better?

If your immune system is working properly it is very likely that you will get better and be left with no ill effects. If you have a long-term problem with your immune system, however, you stand more of a risk of developing complications. The prospects for people who are HIV-positive and have become infected with toxoplasma have improved considerably since the use of a treatment called antiretroviral therapy (ART), also called highly active antiretroviral therapy (HAART).

Can toxoplasmosis be prevented?

All people should follow the advice below. However, the advice is particularly important for women who are pregnant and people who are HIV-positive:

• Wash hands before handling food.

• Thoroughly wash all fruit and vegetables, including ready-prepared salads, before eating them.

• Thoroughly cook raw meats and ready-prepared chilled meals.

• Wear gloves and thoroughly wash hands after handling soil and gardening.

• Avoid cat droppings in cat litter or in soil.

In some countries (such as France), all pregnant women are tested for toxoplasma infection. This does not happen in the UK, because infection rates are much lower.