Toxoplasmosis

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. more...

At least one third of the world population may have contracted a toxoplasmosis infection in their lifetime but, 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 (inflammation of the brain) and neurologic diseases and can affect the heart, liver, and eyes (chorioretinitis).

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.
• Ingestion of raw or unpasteurized milk and milk products, particularly those containing goat's milk.
• 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.

Although the pathogen has been detected on the fur of cats, the pathogen has not been found in a 'ripe' form, and direct infection from handling cats is generally believed to be very rare.

Pregnancy precautions

Congenital toxoplasmosis is a special form in which an unborn child is infected via the placenta. This is the reason that pregnant women should be checked to see if they have a titer to toxoplasmosis. A titer indicates previous exposure and largely ensures the unborn baby's safety. If a woman receives her first exposure to Toxoplasma while pregnant then the baby is at particular risk. A woman with no previous exposure should avoid handling raw meat, exposure to cat faeces, and gardening (a common place to find cat faeces). Most cats are not actively shedding oocysts and so are not a danger, but the risk may be reduced further by having the litterbox emptied daily (oocysts require longer than a single day to become infective), and/or by having someone else empty the litterbox.

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