Schizophrenia is a serious brain disorder that affects nearly 1.1 percent of the adult population in this country. Symptoms generally begin to show up in men in their late teens or early 20s, and in women in their 20s and 30s.

How schizophrenia begins is not clear, but now researchers are looking to a seemingly unlikely source for the disease: cats, or more specifically, a common parasite that is spread by cats to people.

The parasite in question is Toxoplasma gondii (T. gondii), a micro-organism that is known to infect people's brains and thereby alter the neural chemistry. This can, in certain instances, lead to psychotic behavior, or schizophrenia.

While the exact cause of the disorder is not understood, it is believed to be linked to both genetic and environmental factors. Research has suggested that certain viruses can increase the likelihood of developing schizophrenia, including influenza and herpes.

Since so little is really understood about the progression to schizophrenia, all the possibilities must be considered, including the role of infectious agents. The advantage of a viral or microbial basis for schizophrenia is that it opens the door for possible ways to treat and prevent the disease.

Cats usually become infected with T. gondii when they eat an infected animal, such as a mouse. The parasite can infect people through exposure to the cat's fecal matter, whereby most people have little to no symptoms. However, in pregnant women and in situations where a person's immune system is not as strong, the microbe can cause serious problems, including encephalitis, miscarriages in pregnant women, birth defects, and damage to vital organs.

Interestingly, when mice or rats are infected, the organism causes a change in their behavior that makes them more vulnerable to being caught and eaten by a cat, thereby promoting the survival of the parasite. This may have a parallel in human behavior that stems from the same infection, including the production of dopamine, an important behavioral regulator. In fact, some therapeutic drugs to treat schizophrenia target dopamine production or receptors in the brain.

The potential relationship between infectious disease and brain disorders is gaining supporters in the field of medicine. Studies are showing that a variety of viral infections can actually increase the risk of brain damage that could affect behavior patterns.

While the connection between T. gondii and schizophrenia is still not conclusive, there is some compelling evidence that may warrant further investigation, including the fact that people who suffer from schizophrenia have a higher prevalence of antibodies against the parasite. There is also a lower rate of the disease in countries where cats are rare. Finally, some adults who are afflicted with toxoplasmosis show psychological symptoms that are similar to schizophrenia.

For now, more research needs to be done, but medical experts stress that cat owners need not be worried as long as some common sense hygienic practices are used, including washing hands thoroughly before eating and avoiding uncooked meat.

For more information about schizophrenia, visit the website for the National Institutes of Mental Health (NIMH), a division of the National Institutes of Health (NIH).