Olga Skipko has had the good fortune to live most of her adult life in the Polish village of Gruszki, in the heart of the Puszcza Bialowieska, one of Europe's most beautiful forests and home to wolves, lynxes and the endangered European bison. Unfortunately, the forest is also a breeding ground for disease-carrying ticks. Skipko, 49, thinks she was bitten about 10 years ago, when she began having the classic symptoms of Lyme borreliosis, a tickborne nervous-system disease: headaches and aching joints. She didn't get treatment until 1998. "I was treated with antibiotics and felt a bit better," she says.
That was only the beginning of her troubles. A few years later, she began to forget things and her speaking grew labored. It got so bad that she had to quit her job in a nursery forest and check herself in to a psychiatric clinic. "I hope they will help me," she says. "I promised my children that when I come back home, I will be able to do my favorite crosswords again." Doctors ran a battery of tests and concluded that her mental problems were the advanced stage of the Lyme disease she had contracted years ago.
Scientists have long known that some diseases can cause behavioral problems. When penicillin was first used to treat syphilis, thousands of cured schizophrenics were released from mental asylums. Now, however, scientists have evidence that infections may play a far bigger role in mental illness than previously thought. They've linked cases of obsessive-compulsive disorder, bipolar disorder and schizophrenia to a variety of infectious agents, and they're investigating autism, Tourette's and anorexia as well. They're beginning to suspect that bad bugs may cause a great many other mental disorders, too. "The irony is that people talked about syphilis as the 'great imitator'," says University of Louisville biologist Paul Ewald, "but it may be the 'great illustrator'--a model for understanding the causes of chronic diseases."
Mental illnesses constitute a large and growing portion of the world's health problems. According to the World Health Organization, depression is one of the most debilitating of diseases, on a par with paraplegia. Psychiatric illnesses make up more than 10 percent of the world's "disease burden" (a measure of how debilitating a disease is), and are expected to increase to 15 percent by 2020. Much of this may be the work of viruses, bacteria and parasites. Psychiatrist E. Fuller Torrey, of the Stanley Medical Research Institute in Maryland, has found from studying historical asylum records that hot spots--higher-than-normal incidences--of mental illness can shift, much like infectious-disease outbreaks, which lends credence to the notion that infectious agents play a big role. "Mental disorders are the major chronic recurrent disorders of youth in all developed countries," says Harvard policy expert Ronald Kessler, who directs the WHO's mental-health surveys.
Perhaps the most well known disease that's been linked to mental disorders is Lyme disease, which is caused by the Borrelia burgdorferi germ. First identified in the mid-1970s among children near Lyme, Connecticut, the disease has long been known to cause nervous-system problems and achy joints if left untreated. Now scientists are finding that Lyme disease can also trigger a whole smorgasbord of psychiatric symptoms, including depression. One New York man (we'll call him Joe) found out firsthand how debilitating the disease can be. When he began having bouts of major depression back in 1992, he had forgotten all about the tick bite he had gotten four years earlier. He spent two years in a blur of antipsychotic drugs, mental institutions, jails and suicide attempts. On a hunch, a doctor at a psychiatric hospital in New Jersey had Joe tested for Lyme disease. After an intensive course of antibiotics, Joe's improvement was dramatic and immediate. "I started to have this fog lift," he recalls. Still, he will probably have to be on psychotropic drugs for the rest of his life.
Some psychiatrists fret that there may be thousands of people suffering from Lyme-induced depression without knowing why. Not only is Lyme disease tricky to diagnose--not everybody gets the circular rash, and lab tests still aren't wholly reliable--it can take a decade or more for mental disorders to set in. The U.S. Centers for Disease Control says that nine out of 10 cases of Lyme diseases remain unreported. There are 15 species of borellias--making them the most common tickborne disease-producing bacteria in the world.
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.