Toxoplasmosis
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Toxoplasmosis is a parasitic disease caused by the parasite Toxoplasma gondii. It infects most animals and causes human parasitic diseases, but the primary host is the felid (Cat family). People usually get infected by eating raw or undercooked meat, or more rarely, by contact with cat faeces.
Congenital toxoplasmosis is a special form in which an unborn child is infected via the placenta. The danger of congenital toxoplasmosis is the reason that pregnant women should avoid contact with cat faeces. Direct infection from handling cats is thought to be rarer.
At least one third of the world population may have contracted a toxoplasmosis infection in their lifetime, after the acute infection has passed the parasite rarely causes any symptoms in otherwise healthy adults. However, people with a weakened immune system are particularly susceptible, such as people infected with HIV. The parasite can cause encephalitis (infection of the brain) and neurologic diseases and can affect the heart, liver, and eyes (chorioretinitis).
Treatment is very important for recently infected pregnant women, to prevent infection of the foetus. Since a baby's immune system does not develop fully for the first year of life, and the resilient cysts that form throughout the body are very difficult to eradicate with antibiotics, an infection can be very serious in the very young.
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Transmission
Transmission may occur through:
- Ingestion of raw or partly cooked meat, especially pork, lamb, or venison, or by hand to mouth contact after handling undercooked meat. Infection prevalence is higher in countries that traditionally eat undercooked meat, such as France. This seems to be by far the most common route of infection.
- Accidental ingestion of contaminated cat faeces. This can occur through hand to mouth contact following gardening, cleaning a cat's litter box, children's sandpits, or touching anything that has come into contact with cat faeces.
- Contamination of knives, utensils, cutting boards and other foods that have had contact with raw meat.
- Drinking water contaminated with Toxoplasma.
- The reception of an infected organ transplant or blood transfusion, although this is extremely rare.
The cyst form of the parasite is extremely hardy, capable of surviving exposure to cooling down to subzero temperatures and chemical disinfectants such as bleach and can survive in the environment for over a year. It is however susceptible to high temperatures, and is killed by cooking. Cats excrete the pathogen for a number of weeks or months after contracting the disease, generally by eating an infected rodent. Even then, cat faeces are not generally contagious for the first day or two after excretion, after which the cyst 'ripens' and becomes potentially pathogenic.
Symptoms
Infection has two stages. During acute toxoplasmosis, symptoms are often flu-like: swollen lymph nodes, or muscle aches and pains that last for a month or more. Rarely, a patient with a fully functioning immune system may develop eye damage from toxoplasmosis. However, most patients who become infected with toxoplasmosis do not know it. In most non-immunodeficient patients, the infection enters a latent phase, during which only bradyzoites are present, forming cysts in nervous and muscle tissue. Young children and immunocomprimised patients, such as those with HIV/AIDS, those taking certain types of chemotherapy, or persons who have recently received an organ transplant, may develop severe toxoplasmosis. This can cause damage to the brain or the eyes. Most infants who are infected while in the womb have no symptoms at birth but may develop symptoms later in life. Only a small percentage of infected newborns have serious eye or brain damage at birth.
Recent evidence (http://www.biomedcentral.com/1471-2334/2/11) shows that the latent phase of the infection previously considered asymptomatic, may cause behavioral changes in infected patients, as it has previously been shown to do in mice. The changes observed are likely due to the presence of cysts in the brain.
Risk factors
- Infants born to mothers who became infected with Toxoplasma for the first time during or just before pregnancy.
- Persons with severely weakened immune systems, such as persons with AIDS. This results from an acute Toxoplasma infection or an infection that occurred earlier in life that reactivates and causes damage to the brain, eyes, or other organs.
Human prevalence
In the U.S. NHANES III national probability sample, 22.5% of 17,658 persons >12 years of age had Toxoplasma-specific IgG antibodies, indicating that they had been infected with the organism. It is thought that between 30% and 60% of the world's population are infected.
References
- CDC factsheet: Toxoplasmosis (http://www.cdc.gov/ncidod/dpd/parasites/toxoplasmosis/factsht_toxoplasmosis.htm)
- CDC document: Toxoplasma gondii Infection in the United States, 1999 – 2000 (http://www.cdc.gov/ncidod/eid/vol9no11/03-0098.htm)
- Article expounding the link between Traffic accidents and Toxoplasmosis (http://www.biomedcentral.com/1471-2334/2/11)
Note: parts of this article are taken from the public domain CDC document CDC factsheet: Toxoplasmosis (http://www.cdc.gov/ncidod/dpd/parasites/toxoplasmosis/factsht_toxoplasmosis.htm). de:Toxoplasmose es:Toxoplasmosis fr:Toxoplasmose ms:Penyakit Toxoplasmosis pl:Toksoplazmoza sk:Toxoplazmóza