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Schizophrenia is one of the most common mental diseases in the world, affecting about 1 percent of people, but it has vexed medical researchers for decades. We still know very little about how this devastating mental illness begins. A promising new line of research, though, is making waves by tracing it to a previously unexpected source: viral infection during infancy.

If this theory is borne out, it would constitute a sea change in how we understand and treat schizophrenia, Douglas Fox writes in Discover magazine (June 2010):

“The implications are enormous. [Researchers] hold out hope that they can address the root cause of schizophrenia, perhaps even decades before the delusions begin. . . . The results could lead to meaningful new treatments not only for schizophrenia but also for bipolar disorder and multiple sclerosis.”

A key player behind the “insanity virus” theory is Fuller Torrey, director of the Stanley Medical Research Institute in Chevy Chase, Maryland. His sister Rhoda has spent 40 years in state hospitals, suffering from schizophrenia; he has spent the last 30 searching for clues to the mysterious disease.

In his early research Torrey noticed several things about schizophrenia that led him to explore it as a brain disease, not simply a psychological problem. For example, schizophrenics show signs of inflammation in their white blood cells, which fight infection, and they lose brain tissue as the disease progresses. Moreover, in an unexplained oddity known as the birth-month effect, people born in winter and early spring are more prone to schizophrenia.

Torrey and another researcher, infectious-diseases specialist Robert Yolken, went looking and found evidence that schizophrenics had previously suffered from infections, including toxoplasmosis, a parasite spread by house cats.

Separately, another researcher, Hervé Perron, made a breakthrough discovery, learning that everyone carries the virus that causes multiple sclerosis. It’s embedded in our DNA, the legacy of a rare retrovirus inherent in the human genome. And in people with MS, this “viral stowaway” has been switched on to cause MS symptoms. Torrey, Yolken, and others now think schizophrenia works in much the same way, caused by a retrovirus called HERV-W.

“The first, pivotal infection by toxoplasmosis or influenza might happen shortly before or after birth,” writes Fox in Discover. “That would explain the birth-month effect: Flu infections happen more often in winter. The initial infection could then set off a lifelong pattern in which later infections reawaken HERV-W, causing more inflammation and eventually symptoms.”

It’s a bold theory that upends much previous scientific research into schizophrenia, but Perron has started a Swiss biotech company, GeNeuro, to develop treatments that target HERV-W, and he hopes to begin clinical trials this year.

Some skepticism remains, Discover reports, but if the trials work, “the questions may be silenced—and so may the voices of schizophrenia.”

This article first appeared in the March-April 2011 issue of Utne Reader.