Toxoplasmosis is a disease caused by a microscopic parasite called Toxoplasma gondii. It is not a new disease, having first been discovered in 1908. Since its discovery, Toxoplasmosis has been found in virtually all warm-blooded animals including most pets, livestock and people. Nearly one-third of all adults in the U.S. and in Europe have antibodies in Toxoplasma, which means they have been exposed to the parasite.
There are 3 principal ways Toxoplasmosis is transmitted:
Pigs, sheep, goats and poultry are sources of meat commonly infected with Toxoplasma. Toxoplasma in meat can be killed by cooking at 152°F (66°C) or higher or freezing for a day in a household freezer. Cats are the definitive host for the production of the infectious and resistant Toxoplasma oocysts. The oocyst, released from the intestine of cats in their feces, is very hardy and can survive freezing-even several months of extreme heat and dehydration. Moreover, oocysts can be carried long distances in wind and water.
There are two populations at high risk for disease with Toxoplasma: pregnant mothers and immuno-deficient individuals. In the United States it is estimated that approximately 3,000 children are born infected with Toxoplasmosis every year. Although the majority of infected infants show no symptoms of Toxoplasmosis at birth, many are likely to develop signs of infection later in life.
Children congenitally infected with Toxoplasma may suffer from loss of vision, mental retardation, loss of hearing, and death in severe cases. Ideally, women who have frequent contact with cats should be serologically tested for Toxoplasma gondii before becoming pregnant, because if they are already seropositive, they are not at risk of acquiring a primary infection.
Usually, people suffering from both Acquired Immune Deficiency Syndrome (AIDS) and Toxoplasmosis have been exposed to the Toxoplasma parasite earlier in life, and the HIV infection simply allowed the Toxoplasma parasite to grow unchecked. These patients develop neurologic diseases and can experience convulsions, paralysis, coma or possibly die from Toxoplasmosis even after treatment is administered.
Although cats can be infected by the same means as people, the most likely sources of Toxoplasma in cats are from eating infected mice, birds, and other small animals
For indoor cats, the most likely source is uncooked meat scraps. When a cat is exposed to Toxoplasma through the consumption of infected meat or tissues, they can excrete millions of Toxoplasma oocysts in their feces each day. This release of oocysts can continue for up to two weeks.
Oocysts in feces become infectious (reach Stage F) after one or two days. Since most cats do not leave feces on their fur for two days, it is unlikely that humans become infected from direct contact with cats themselves. Because cats usually exhibit no signs of illness while passing oocysts, it is difficult to determine when a particular cat's feces may be infectious to people or other mammals. Most adult cats will not pass oocysts ever again after recovering from an initial exposure to Toxoplasma; but again, regardless of when Toxoplasma oocysts were initially passed through the cat's feces, the oocysts themselves can remain infectious and persist in the environment for months.
Although cats infects with Toxoplasma rarely show symptoms of Toxoplasmosis, there have been cases in cats associating Toxoplasmosis with pneumonia, liver damage, and loss of vision. Why some cats show symptoms and other cats do not is not known. Concurrent infection with other diseases (feline leukemia, FIV) can aggravate Toxoplasmosis in cats. Treatment can be effective if the disease is diagnosed early. A blood test for Toxoplasma antibodies helps in diagnosis of Toxoplasmosis in sick cats.
** This information has been prepared as a service by the American Veterinary Medical Association.
Talk to your veterinarian if you have questions about Toxoplasmosis and pets.
For questions about Toxoplasmosis in humans, consult your family physician!
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