Toxoplasmosis is a disease caused by infection with a protozoan (a tiny, single-celled animal) called Toxoplasma gondii. T. gondii is a parasite that spends most of its life cycle inside the digestive tract of a cat or in farm animals such as cattle or sheep. In these species, T. gondii seldom causes any significant symptoms of toxoplasmosis. Humans acquire the disease when they come in contact with an infected cat’s faeces or eat or drink infected animal products.
Symptoms of Toxoplasmosis
Human toxoplasmosis occurs when T. gondii is accidentally ingested as a result of:
- not washing the hands properly after handling an infected cat’s litter box or gardening in a plot that an infected cat uses as a toilet
- eating unwashed root vegetables from such a plot
- playing in a sandpit where an infected cat may have defecated
- eating cured or undercooked meat or drinking unpasteurized milk from an infected animal.
In up to one-quarter of cases in humans, T. gondii infection causes no ill effects. In many others, the symptoms of toxoplasmosis are a flu-like illness with fever, muscle pains and a headache. The most common reason for people to visit their doctor with toxoplasmosis is swollen, tender lymph nodes. The disease may be more severe in young children and in those with a weakened immune system.
Once the initial infection has cleared up, T. gondii may form cysts in various tissues within the body. If these cysts become reactivated at any time in the future, the symptoms of toxoplasmosis recur.
Ocular Toxoplasmosis – Congenital Disease Due to Toxoplasmosis in Pregnancy
While toxoplasmosis is generally a mild illness in healthy adults, it becomes a more serious issue when a woman is infected during pregnancy. The woman herself may show no ill-effects, but T. gondii infection is passed on to one-third to one-half of babies born to an infected mother. These infants often have no symptoms at birth, but many develop signs of congenital toxoplasmosis in adolescence.
Symptoms of congenital toxoplasmosis include low birth weight, hearing loss, mental retardation and seizures. Adolescents who were not treated for the infection as babies are likely to suffer ocular toxoplasmosis due to T. gondii cysts deposited in the retina of the eye. Ocular toxoplasmosis leads to reddening and pain in the eye, visual disturbances and floaters. The optic nerve and blood vessels to the eye may also be affected, and anterior uveitis may develop. The most severe cases can result in partial or total blindness.
Testing for Toxoplasmosis and Treatment of T. gondii Infection
Laboratory tests on a blood sample are the best way to diagnose toxoplasmosis. An MRI scan may show T. gondii cysts in the brain and other parts of the body. Fetal growth abnormalities associated with congenital toxoplasmosis may be visible on an obstetric ultrasound scan.
Treatment for toxoplasmosis is not generally needed in otherwise healthy adults, as the infection usually clears up by itself. Pregnant women, people with a weakened immune system and infants with congenital toxoplasmosis are prescribed anti-protozoal drugs to kill the parasites. Babies who are at risk of losing their sight may also be given steroids.
Toxoplasmosis and Cats, Meat and Milk
Cat owners should not be unduly worried about catching toxoplasmosis from their pets. T. gondii in cats is contagious for only a couple of weeks after the cat is first infected and cannot be transmitted by touching a cat’s fur or even by being scratched or bitten. In the USA, more people contract toxoplasmosis from infected food than from cat faeces.
However, it is sensible for pregnant women not to handle cat litter boxes, and to wear gloves for gardening, avoid undercooked or cured meat and unpasteurized milk, and wash fruit and vegetables thoroughly before eating. With simple precautions such as these, the risk of congenital toxoplasmosis is greatly reduced.
References:
MedlinePlus.Congenital Toxoplasmosis (accessed November 2, 2010).
Ho-Yen DO. Toxoplasmosis. Medicine 2005; 33(5): 120−1.
Cornell University, College of Veterinary Medicine. Toxoplasmosis in Cats (accessed November 2, 2010).
Disclaimer:
The information contained in this article is for educational purposes only and should not be used for diagnosis or to guide treatment without the opinion of a health professional. Any reader who is concerned about his or her health should contact a doctor for advice.
