Several prominent researchers believe that exposure to cats could be behind some forms of mental illness like schizophrenia or manic depression.

An estimated 10 percent of all cats carry a parasite like the one that causes a human infection called toxoplasmosis. The condition is especially dangerous for pregnant women because it can cause malformations, like mental retardation, or even kill an unborn child.

"We know that toxoplasmosis in some individuals -- if it gets in the brain -- can cause symptoms that are similar to schizophrenia," Dr. Fuller Torrey, of Uniformed Services University Health Sciences, said.

Torrey, a leading schizophrenia researcher, said that there is now growing evidence to show a toxoplasmosis infection could also be behind some cases of schizophrenia.

"We have found that there's an elevated antibodies to toxoplasmosis in the spinal fluid of people who have acute onset schizophrenia," Torrey said.

Antibodies, which are evidence of toxoplasmosis, have also been found in mothers who have given birth to children who later developed schizophrenia. Researchers have also looked at the rate of some mental illnesses in those who had been exposed to cats as children versus those who hadn't. They said that in two separate studies, people who suffered from schizophrenia and manic depression had more exposure to cats in childhood.

Those who research treatments for schizophrenia believe that the reality is this theory may fail.

"I remember people getting excited about a particular virus in New York as a cause of Alzheimer's disease and it turned out to be not at the cause of Alzheimer's disease, so we'll have to wait and see," Dr. Anne Andorn, of the University of Texas, said.

Torry said that cat owners should also take that wait and see attitude when it comes to his theory.

"I don't think anybody should panic and put their cats out," Torry said. "On the other hand, I have a grandchild. For example, if my daughter would ask me should we get a cat when we have a small child -- my answer should be no."

Part of that awareness begins with who comes knocking at your door. When pregnant friends visit, remind them not to touch the cat -- even if it's an indoor cat who isn't exposed to rats or mice, the source of the parasite.

If you are pregnant, have someone else clean the litter box. Cat feces is the biggest source of toxoplasma infection in the country. And remember, experts aren't saying you should get rid of your cat -- just be aware of the problem.

There is a test that can be done to see if your cat is a carrier of the toxoplasma parasite. Click here for more information.

Additional Resources:

• Tips On Preventing Exposure To Toxoplasma (Especially During Pregnancy)
• Cat Fanciers' Association article