Viruses and Mental Illness

Flu, AIDS, meningitis, Ebola, polio, herpes, measles, rabies—the list of diseases caused by viruses is a litany of woe ranging from the merely annoying to the deadly. Every year almost two million people are killed by the human immunodeficiency virus (HIV), and around half that many people succumb to viral hepatitis infections. The economic toll of viral illnesses is nearly as staggering as the human one; flu costs the United States an estimated $25 billion a year, and HIV costs $36 billion. To make matters worse, new viruses continue to appear (see “Virus Hunter” below), often after hiding in animal populations for centuries before moving into humans—as did HIV, avian flu, and severe acute respiratory syndrome (SARS). But while public health officials and physicians focus on the threat of emerging viruses, little-noticed research is implicating these primitive microbes in diseases long thought to have nothing to do with them: mental illnesses.
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At first the evidence for a viral link to mental illness was spotty and inconsistent. Early studies piggy-backed on observations that when mothers suffered an infection during pregnancy, the children who were in utero at the time had an elevated risk of developing schizophrenia. But rigorous studies of whether that link was real produced contradictory results: Some found that maternal infection with influenza increased the risk of a child developing schizophrenia 20 years later, but others did not. Only in the last few years have scientists sorted it out. Instead of assuming that every child who had been in utero at the time of a flu outbreak had been infected, researchers began examining mothers’ blood for the telltale antibodies that indicate a past infection. With that advance, the link became clear: As researcher Alan Brown of Columbia University calculated in a 2010 paper, more than 30 percent of the risk of developing schizophrenia comes from prenatal exposure to the flu virus.