Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Toxoplasmosis Incidence Is Not Related to Cat Ownership

Pet Column for the week of October 17, 2005

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Kim Marie Labak
Information Specialist

Toxoplasmosis is an illness that has received much attention from the media for its association with cats. Dr. Thomas Graves, veterinary internal medicine specialist at the University of Illinois Veterinary Teaching Hospital in Urbana, explains that contrary to what many people believe, there is no correlation between incidence of human toxoplasmosis infection and cat ownership.

Toxoplasmosis is a disease caused by the protozoal parasite Toxoplasma gondii, which can affect all warm-blooded species. People can get infected by eating raw or undercooked meat that contains Toxoplasma cysts, or by ingesting those cysts from the environment.

Cats that have been recently infected can shed infective toxoplasma organisms in their feces, which is why many people may associate cats with the disease. However, Dr. Graves explains there are many reasons that cats dont deserve notoriety for the disease.

"First of all, 30 percent to 50 percent of people have already been exposed to toxoplasma, and most of these people do not get sick." Most people and animals show mild or no signs of illness when infected with toxoplasma. People and animals most at risk for developing disease include those with suppressed immune systems, for example, from HIV infection or chemotherapy treatment, and unborn fetuses that can get infected through maternal blood. In these cases, toxoplasmosis may manifest as a blood, respiratory, or nervous system disease.

Additionally, the likelihood an indoor cat will shed infective toxoplasma is very low. A cat will only shed the organism if it has been recently exposed. This usually happens in kittenhood if it will happen at all. When exposed, a cat will shed the organism for one to three weeks, and if even if it doesn't get sick, it will develop antibodies to protect it against future infection. Once a cat has developed these antibodies, the chances it will shed toxoplasma again are very slim.

Finally, the developmental stage of toxoplasma found in cat feces takes several days to mature into the infectious stage once they are out of the cat's body. Dr. Graves explains, "If litter boxes are cleaned daily, there's little chance cat owners can be exposed to the infectious form of the organism."

Dr. Graves points out that the immune status of the human plays a role in whether a person or unborn fetus can become infected. A blood serum test can determine if a person has antibodies to protect against toxoplasmosis. If the blood contains antibodies, the person has already been exposed, and is protected from infection.

If a person is negative for toxoplasmosis, then his cat can also be tested for antibodies. There are two antibodies that a veterinarian will look for: Immunoglobulin M, or IgM, which is produced soon after infection, and Immunoglobulin G, or IgG, which doesnt increase until five weeks after the cat has been infected.

If a cat is negative, it poses no risk to owners. If the cat has high level of IgM, it was recently infected, and owners should take precautions against exposure. If the cat has high level of IgG, it has been exposed, but likely has already stopped shedding the organism.

"Pregnant women and immuno-suppressed people do not have to avoid cats," says Dr. Graves. "With some common sense and proper hygiene, those at risk can avoid ingestion of the infectious oocyts."

Of course, the best way to protect the humans in your family from toxoplasmosis is by protecting your cats from infection. Dr. Graves recommends keeping pet cats indoors, and they should not eat raw meat, such as birds or rodents.

Women who are pregnant, or plan on becoming pregnant, can be tested and have their cats tested for antibodies. Litter boxes should be cleaned daily, especially if antibody tests indicate that a cat has been recently exposed to toxoplasma, and pregnant women should avoid this household task. Toxoplasmosis is just one of many reasons pet owners should wash their hands thoroughly after cleaning up after their pets.

Since recently infected outdoor cats can deposit toxoplasma into the environment, pregnant women and immuno-suppressed individuals should wear gloves when gardening or doing other outdoor work, and thoroughly wash their hands afterward. Covering sandboxes when they not in use can prevent cats from using them as a litter box.

For more information about toxoplasmosis, consult your veterinarian and your physician.