Toxoplasmosis is a common infection that occurs in most birds and mammals, including humans.

Signs of toxoplasmosis include mild flu-like symptoms, such as high temperature, sore throat and aching muscles. However, in most cases, toxoplasmosis doesn't cause any symptoms.

Toxoplasmosis can cause serious complications in people with weakened immune systems, such as those with HIV and AIDS or cancer.

Read more about the complications of toxoplasmosis.

Congenital toxoplasmosis is also more serious and occurs when a woman becomes infected during pregnancy and passes the infection on to her unborn baby. This can result in the baby developing serious health problems such as blindness and brain damage.

Read more about the symptoms of toxoplasmosis.

What causes toxoplasmosis?

Toxoplasmosis is caused by infection with a common parasite called Toxoplasma gondii (T. gondii). T. gondii can be found in:

• undercooked or raw meat
• cured meat, such as parma ham or salami
• unpasteurised goats' milk
• cat faeces
• soil or cat litter that is contaminated with infected cat faeces

It cannot be passed from person to person, other than in very rare cases of organ transplantation.

Treating toxoplasmosis

Most cases of toxoplasmosis do not need treatment.

Medication is only prescribed if the symptoms of toxoplasmosis are more severe, particularly in people with a weakened immune system. Pyrimethamine and sulfadiazine will often be prescribed to treat these patients.

Pregnant women who become infected with toxoplasmosis for the first time may be prescribed antibiotics. This is to reduce the risk of the unborn baby becoming infected and to limit the severity of congenital toxoplasmosis if the baby does become infected.

Read more about treating toxoplasmosis.

Who is affected by toxoplasmosis?

Up to a third of the UK population will have a toxoplasmosis infection at some point in their lives. Once infected, a person is immune from further infection for life.

Toxoplasmosis in pregnancy and congenital toxoplasmosis are rare, with about three babies in every 100,000 born with the condition in the UK.

Read more about:

• Toxoplasmosis complications
• Preventing toxoplasmosis
• Treating toxoplasmosis

In about 80% of cases, toxoplasmosis does not cause any symptoms and a person who is infected will not be aware that they are infected.

The immune system of healthy adults and children is usually strong enough to prevent the parasite that causes toxoplasmosis (Toxoplasma gondii or T. gondii) from causing serious illness. Once you have had the infection you become immune to it and T. gondii will live harmlessly in your body for life.

In some cases, toxoplasmosis can cause the lymph nodes (glands that form part of your immune system) to swell, particularly in the throat or armpits. This can lead to symptoms that are similar to the flu, such as:

• aching muscles
• fever of 38°C (100.4°F) or over
• tiredness
• feeling sick
• sore throat

It is very rare for otherwise healthy people to experience any serious symptoms of toxoplasmosis.

Pregnant women

If you develop a toxoplasmosis infection either while you are pregnant or shortly before you conceive there is a chance that you could pass the infection on to your unborn baby. This is known as congenital toxoplasmosis.

You will probably not experience any symptoms of the infection yourself, but an infection that develops during the early stages of pregnancy increases the risk of:

• miscarriage - the loss of a pregnancy during the first 23 weeks
• stillbirth - where a baby is born after 24 weeks of pregnancy without any signs of life

One large study found that toxoplasmosis caused stillbirth in pregnant women in just less than 1% of cases.

About 30-40% of pregnant women who acquire toxoplasmosis infection during their pregnancy will pass the infection on to their unborn baby, leading to congenital toxoplasmosis.

Congenital toxoplasmosis

The symptoms of congenital toxoplasmosis vary depending on when the mother becomes infected. Symptoms will usually be more severe if the mother is infected around the time she becomes pregnant or during the first or second trimester (up to week 27 of the pregnancy).

Symptoms of congenital toxoplasmosis can include:

• hydrocephalus - water on the brain
• brain damage
• epilepsy - a condition that affects the brain and causes repeated seizures (fits)
• jaundice - yellowing of the skin and whites of the eyes
• deafness
• eye infections and blindness
• an enlarged liver or spleen (an organ that filters impurities from your blood)
• growth problems
• cerebral palsy - a condition of the brain and nervous system that affects a child’s movement and co-ordination

If the mother becomes infected during the third trimester of pregnancy (from week 27 to the birth), and the infection passes on to the baby, he or she may not have any symptoms at birth. However, complications may develop later in life.

For example, months or years later a child born with congenital toxoplasmosis may develop eye infections, hearing loss or learning difficulties.

Read more about the complications of congenital toxoplasmosis.

People with immune deficiencies

For someone with a weakened immune system, toxoplasmosis can be fatal. This is because their body may not be able to fight off the infection. Your immune system can be weakened if you:

• have an illness that affects your immune system, such as HIV and AIDS or cancer
• are receiving certain types of medication, such as chemotherapy (powerful cancer-killing medication)
• are taking immunosuppressant medication, for example after having had an organ transplant

There is also a risk of permanent eye or brain damage when toxoplasmosis infects someone with a weakened immune system.

If toxoplasmosis begins to affect the brain, it can cause encephalitis. This is sometimes called toxoplasmosis encephalitis (TE) and it is one of the most frequent causes of death in people with AIDS.

Symptoms of TE include:

• headaches
• confusion
• poor co-ordination
• seizures (fits)
• chest pains
• coughing up blood
• difficulty breathing
• a high temperature (fever) of 38°C (100.4°F) or over
• vision problems, such as blurred vision and floaters (small pieces of debris that can cloud your vision)
• multiple lesions (wounds) in the brain

The toxoplasmosis infection is caused by the Toxoplasma gondii (T. gondii) parasite.

Some of the ways in which you may come into contact with this parasite are outlined below.

• Contact with cat faeces - either in a litter tray or in soil. The parasite breeds in the bowels of cats and is released in their faeces. Cat faeces can also contaminate soil, fruit and vegetables, water and other animals.
• Undercooked or raw infected meat - either by eating it or touching your mouth after handling it. Grazing animals can become infected after eating contaminated grass and animal feed. Venison, lamb and pork are more likely to be infected.
• Contaminated knives, cutting boards and other utensils that have been in contact with contaminated, undercooked or raw meat.
• Eating or drinking infected unpasteurised goats' milk or products that are made from it, such as cheese.

There is also a small risk that the toxoplasmosis infection could be passed on from sheep during the lambing season. This is because the T. gondii parasite is sometimes found in the afterbirth and on newborn lambs after an infected sheep has given birth.

Toxoplasmosis cannot be passed on through person-to-person contact. This means that:

• you cannot catch toxoplasmosis from contact with a person who is infected
• you cannot pass toxoplasmosis on to your children if you have previously had the infection
• it is not possible to pass the infection on through breastfeeding

However, in very rare cases, people have developed toxoplasmosis from an infected organ transplant or blood transfusion.

Congenital toxoplasmosis

Congenital toxoplasmosis is where a baby is born with toxoplasmosis. The mother passes the infection on to her baby through the placenta (the organ that links the mother’s blood supply to her unborn baby’s).

However, congenital toxoplasmosis can only occur if the mother becomes infected for the first time either while she is pregnant or shortly before conceiving. Congenital toxoplasmosis is more likely to occur if a woman becomes infected later in her pregnancy.

For example, if you become infected around the time of conception, there is less than a 5% chance that your baby will also develop the infection. However, if you become infected during the third trimester of your pregnancy (from week 27 until the birth), there is about a 65% chance that your baby will also be infected.

One study calculated that for every week further along the pregnancy that the mother was infected, the likelihood of the toxoplasmosis infection being passed on to her baby increased by 12%.

If you are infected with the Toxoplasma gondii (T. gondii) parasite, your immune system will start producing antibodies to fight it.

If toxoplasmosis is suspected, you will have a blood test to check for antibodies.

Antibodies are proteins that neutralise or destroy disease-carrying organisms and toxins (poisons).

Negative result

Occasionally, early testing can produce a negative result even when a person is infected. This is known as a false negative and happens when the body has not had a chance to start producing antibodies to the parasite, which usually takes up to 23 days after someone is initially infected.

Your GP may recommend that you have another blood test two to three weeks later. If the result is still negative, it is very unlikely that you have the toxoplasmosis infection.

Positive result

A positive result does not necessarily mean that you have an active toxoplasmosis infection. After having toxoplasmosis, the antibodies will remain in your blood for the rest of your life, protecting you from being infected again by the parasite. A positive result usually shows that you have been infected at some point in the past.

To find out whether you have a new infection, you will need more blood tests, which will be sent to a laboratory to be analysed. Checking the levels of antibodies in your blood a second time can help to determine when the infection occurred. For example, if the levels of antibodies are:

• increasing, it would suggest a new, active infection (perhaps a few weeks old)
• still the same, it would suggest an old infection and that you are now immune
• decreasing, it would suggest a recent infection that is no longer active (perhaps a few months old)

Specialised testing is important if you are pregnant or if you have a weakened immune system.

Pregnant women

If you are pregnant and tests confirm that you have a recent toxoplasmosis infection, you will need to have a further test to determine whether your unborn baby is also infected.

Amniocentesis  is the most effective and commonly used test and can be carried out at around 15 weeks of pregnancy. It involves inserting a fine needle through the mother's abdomen to collect a sample of amniotic fluid (the fluid that surrounds the foetus in the womb). The sample will be tested for toxoplasmosis.

Amniocentesis usually takes between 10 minutes and half an hour. You may find the procedure slightly uncomfortable. The procedure carries around a 1% risk of causing a miscarriage.

Read more about amniocentesis.

Congenital toxoplasmosis

Amniocentesis can confirm whether your baby has congenital toxoplasmosis. However, it cannot determine whether the infection has caused any damage to your unborn baby and, if it has, how much.

If your unborn baby has congenital toxoplasmosis, treatment with medication will be started as soon as possible. After your baby is born, he or she will be examined for any signs of damage from the infection, and treatment may continue.

If necessary, your baby will continue to have blood tests for up to a year, or possibly longer, until the test results for toxoplasmosis antibodies are negative. When results indicate that there are no antibodies, your baby has been shown to be infection free.

Immune deficiencies

If you have a weakened immune system, for example due to chemotherapy, routine blood tests for antibodies can produce a false negative. This is because it is possible that your immune system will not produce antibodies to fight off the infection.

Your doctor may request the following tests:

• computerised tomography (CT) scan - where several X-rays are taken at slightly different angles and assembled by a computer to produce a clear, three-dimensional image of the inside of your brain
• magnetic resonance imaging (MRI) scan - where a strong magnetic field and radio waves are used to produce detailed images of the inside of your brain

The test results will reveal if you have any lesions (wounds) in your brain, which occur in many cases of toxoplasmosis.

New research

New research is looking at other ways of diagnosing toxoplasmosis, for example, by identifying the DNA of the T. gondii parasite in samples of cerebrospinal fluid (the fluid that surrounds your brain and spinal cord).

It is hoped that this may be quicker and more reliable by confirming that the damage to the brain has been caused by toxoplasmosis and not by another condition.

The advice outlined below may help to reduce your risk of developing toxoplasmosis infection.

• Wear gloves when gardening, particularly when handling soil - also, wash your hands thoroughly afterwards with soap and hot water.
• Do not eat raw or undercooked meat - particularly lamb, pork and venison, including any ready-prepared chilled meals. Cook all red meat until no trace of pinkness remains and the juices run clear. Do not taste meat before it is fully cooked. Wash your hands thoroughly after handling raw meat.
• Wash all kitchenware thoroughly after preparing raw meat.
• Always wash fruit and vegetables before cooking and eating - this includes ready-prepared salads.
• Avoid drinking unpasteurised goats' milk or eating products that are made from it.
• Do not handle or adopt stray cats.
• Avoid cat faeces in cat litter or soil - wear gloves if you are changing a cat’s litter tray and wash your hands thoroughly afterwards. If you are pregnant or immune deficient, ask someone else to change it for you.
• Feed your cat dried or canned cat food rather than raw meat.

It is important that pregnant women and those with a weakened immune system follow this advice to avoid becoming infected.

Pregnant women should avoid contact with sheep and newborn lambs during the lambing season because there is a small risk that an infected sheep or lamb could pass the infection on at this time.