General Information on Toxoplasmosis

Toxoplasmosis is a disease caused by a common parasite called Toxoplasma gondii, which can infect all mammal and bird species and is found throughout the world. Nearly all warm blooded animals can be infected with toxoplasma but cannot pass on the infection unless they enter the foodchain. It has been estimated that up to one billion of the world's human population has become infected with the parasite.

In England and Wales disease due to toxoplasmosis is reported relatively rarely. However, as symptoms in healthy people are generally mild and non-specific, a significant proportion of cases probably go unnoticed. Studies have estimated that between 7-34% of people in the UK have been infected with T. gondii (the proportion increases with age), however the vast majority of these people will not have noticed any symptoms.

Since 2008, the HPA has been collaborating with Public Health Wales (Toxoplasma Reference Unit in Swansea) to review the number of cases of T. gondii infection; these data are published quarterly in the Health Protection Report. About 400 cases are diagnosed annually.

The disease

Most healthy people who acquire toxoplasma infection do not experience any symptoms, however about 10-15% of people may develop a mild flu-like or glandular fever-like illness. The parasite can form microscopic cysts throughout the body where they remain for many years or decades. These cysts are believed not to pose any risk to people with healthy immune systems. There is some research suggesting possible links between toxoplasma infection and behavioural changes in mammalian hosts, including humans. However, there is insufficient evidence to draw any firm conclusions at this time.

People who have weakened immune systems, such as individuals who are infected with the HIV virus, those who have received an organ transplant, or those taking certain types of chemotherapy are at greater risk of developing severe toxoplasmosis (See 'Toxoplasmosis in the immunocompromised').

Infants born to mothers who became infected with toxoplasma during pregnancy are also at risk of severe toxoplasmosis, as the mother can pass the parasite to the child in the womb (See ' Toxoplasmosis in pregnancy').

Toxoplasmosis of the eye (ocular toxoplasmosis) can sometimes develop, particularly in unborn babies of infected mothers and people with immune deficiencies. However, although rare, eye disease can also develop in healthy people following infection. New evidence indicates that eye disease is a more common outcome of toxoplasma infection in South America, for example, and it has been suggested that certain strains of the organism capable of causing eye disease may be more common in some parts of the world. Symptoms include blurred vision, and 'floaters' (dark spots that pass across your field of vision and move as you move your eye, they may look like clouds, spots, wavy lines or other shapes).

Toxoplasmosis in pregnancy

If a woman becomes infected with toxoplasma for the first time while she is pregnant, although she may not experience any symptoms, the infection can be passed on to her unborn child and cause congenital toxoplasmosis. How severe congenital toxoplasmosis is depends on the stage of pregnancy at which the mother is infected.

The risk of toxoplasma being passed from mother to foetus is lower if the mother becomes infected in early pregnancy. However, if infection of the foetus does occur in early pregnancy, the effects may be more severe and lead to complications such as miscarriage, stillbirth or birth defects. Babies whose mothers are infected late in pregnancy are less likely to experience any problems or symptoms at birth. Complications of the infection may however develop later in life and may not first appear until adulthood. The most common complication recognised in such individuals is ocular disease.

Toxoplasmosis in the immunocompromised

Persons with severely weakened immune systems, such as individuals with HIV/AIDS, those taking certain types of chemotherapy, and those who have recently received an organ transplant, are at greater risk of developing toxoplasmosis. Symptoms include headaches, confusion, seizures, chest pains, coughing up blood and breathing difficulties, and the disease can be fatal in some cases. There is also a risk of developing permanent eye or brain damage.

Transmission

The parasite that causes toxoplasmosis can be found in the faeces of infected cats, and in the meat of infected animals. Cats are the only species in which T. gondii can undergo the sexual part of its life-cycle. The parasite can multiply in the cat's gut lining and be shed in cat faeces in the form of microscopic eggs (oocysts). Once cats have been infected they can spread the parasite in their faeces for a few weeks. Cats do not usually show symptoms when they are first infected, so people may not know if their cat has been infected.

Humans are infected with T. gondii by four major routes:

Swallowing water, food or soil contaminated with the faeces of infected cats
Transmission from a newly infected mother to the foetus
Swallowing or handling undercooked or raw meat (mainly pork or lamb) that contains the tissue cyst form of the parasite
Receiving organ transplants or, very rarely, blood products from donors very recently infected with toxoplasmosis

Other than from mother to foetus, direct human to human transmission has not been reported.

Click here to see the life cycle.

Treatment

In healthy individuals treatment for toxoplasmosis is not usually needed. A range of anti-toxoplasma drug treatments are available for those at greater risk of severe toxoplasmosis.

Prevention

The main way to prevent toxoplasma infection is to take general hygiene precautions to avoid ingesting the parasite. Specific measures also include:

Limiting exposure to cat faeces in cat litter and soil contaminated with cat faeces, particularly when pregnant
Disposing of cat litter daily
Washing hands thoroughly after handling cats, their litter, faeces or soil
Ensuring that surfaces and utensils which have been used in the preparation of raw meat are thoroughly washed, and wash hands thoroughly after handling raw meat
Ensuring that meat is well cooked, to an internal temperature of over 60°C and until it is no longer pink in the middle
Washing all fruits and vegetables before cooking and eating
Wearing gloves when gardening or handling soil, and hands should be washed thoroughly afterwards
Avoiding unpasteurised goat's milk

If you have a long term illness, or are pregnant or planning a pregnancy, you should take extra precautions to avoid being exposed to the parasite. Freezing meat in a domestic freezer for a few days will efficiently kill toxoplasma tissue cysts and may, therefore, help in reducing risk of infection. Cats can become infected by eating infected animals, or eating raw or undercooked meat infected with the parasite. If possible keep your cat indoors and feed it commercial cat food or well cooked food. If possible ask someone else to clean cat litter boxes daily, alternatively wear gloves and wash hands thoroughly afterwards. Litter boxes should be cleaned daily as the parasite in cat faeces needs one or more days after being passed to become infectious.

Further information

NHS Direct

Last reviewed: 25 August 2011