Scientific American Mind
- April 17, 2008
Infected with Insanity: Could Microbes Cause Mental Illness?
Viruses or bacteria may be at the root of schizophrenia and other disorders
By Melinda Wenner
Schizophrenia is a devastating illness. One percent of the world’s population suffers from its
symptoms of hallucinations, psychosis and impaired cognitive ability. The disease destroys
relationships and renders many of its sufferers unable to hold down a job. What could cause such
frightening damage to the brain? According to a growing body of research, the culprit is
surprising: the flu.
If you are skeptical, you are not alone. Being condemned to a lifetime of harsh antipsychotic
drugs seems a far cry from a runny nose and fever. And yet studies have repeatedly linked
schizophrenia to prenatal infections with influenza virus and other microbes, showing that the
children of mothers who suffer these infections during pregnancy are more likely to be diagnosed
with schizophrenia later in life. In 2006 scientists at Columbia University asserted that up to one
fifth of all schizophrenia cases are caused by prenatal infections.
Doctors have known for many years that microbes such as syphilis and
can, if left
untreated, lead to serious psychiatric problems. Now a growing number of scientists are
proposing that microbes are to blame for several mental illnesses once thought to have
neurological or psychological defects at their roots. The strongest evidence pertains to
schizophrenia, but autism, bipolar disorder and obsessive-compulsive disorder have also been
linked to bacterial, viral or parasitic infections in utero, in childhood or in maturity. Some of these
infections can directly affect the brain, whereas others might trigger immune reactions that
interfere with brain development or perhaps even attack our own brain cells in an autoimmune
As scientists tease out the link between infections and psychiatric disorders, they anticipate
opening the door to a new world of preventive measures. In the most immediate cases, a simple
vaccine or regimen of antimicrobial drugs could rid the body of an infection before it damages the
brain. And if our immune system is responsible, we might be able to develop drugs that stifle the
effect of the immune response in the brain. The bottom line is, the more we know about the
complex roots of mental illness, the better we can fight it.
What Causes Mental Illness?
published an editorial entitled “Is Insanity Due to a Microbe?” The
question seemed logical, given that microbes were starting to be implicated in other diseases. In
the editorial, two doctors described how they had injected cerebrospinal fluid of mentally ill
patients into rabbits, which later got sick. The doctors concluded that “certain forms of insanity”
could be caused by infectious agents, “similar to typhoid, diphtheria and others.”
But when Freudian psychoanalysis became popular in the 1930s, the idea was more or less put