Diseases Of The Mind

For its part, the parasite Toxoplasma gondii, which can be found in undercooked meat and cat feces, can lead to full-blown psychotic episodes. Some studies suggest that the parasite stimulates the production of a chemical similar to LSD, producing hallucinations and psychosis. Even when the parasite lies dormant in muscle and brain tissue, it can affect attention span and reaction time in otherwise healthy people. Researchers at Charles University in Prague have discovered that people who test positive have slightly slower-than-average reaction times and--possibly as a result--are almost three times as likely to have car accidents. That's a disturbing prospect, considering that the disease is so widespread: billions of people are thought to be infected.

Even a simple sore throat can lead to psychiatric problems. Few children avoid coming down with a streptococcus infection, also known as strep. Scientists now think that one in 1,000 strep sufferers also develops abrupt-onset obsessive-compulsive disorder (OCD) in a matter of weeks. Strep bacteria trigger OCD by igniting an overzealous response from the immune system, which attacks certain types of brain cells, causing inflammation. Symptoms generally die down after a few months but can flare up again, especially if there's another bout of strep, says Susan Swedo, a childhood-disease expert at the National Institutes of Health. The most effective treatment, still experimental, is to filter out the misbehaving antibodies from the blood. Best is to treat strep early on.

The specter of a depression germ or contagious obsessive-compulsive disorder is unnerving, but it also opens up many more treatment options--antibiotics, vaccines, checking for ticks. Geneticists believe that diseases may trigger the onset of inherited mental illnesses by activating key genes. Avoiding and treating infection may be just as important as the genes you inherit, and a whole lot easier to do something about.

WITH JOANNA KOWALSKA IN WARSAW

© 2003