Did the Microbe Make Me Do It? A Review of Infectious Madness

In recent years there has been a growing accumulation of evidence of the role infectious diseases may have in the development of neuropsychiatric illness. A new book, Infectious Madness: The Surprising Science of How We "Catch" Mental Illness by Harriet Washington, provides an extensive overview of the evidence behind this linkage.

While I don't agree with everything suggested in the book, it is indisputable that several converging lines of evidence exist in this realm. The role of the enteric nervous system, its interaction with the microbiome, and attributes of specific pathogens (e.g. influenza, Toxoplasma, and group A streptococcus) are all fascinating and illustrate the potential role specific infections can have on mental functioning. 

For anyone who has taken care of a person sick with an infection, it is clear that mentation and cognitive ability are adversely effected in a global manner. Also, infections such as rabies and viral encephalitis are obvious examples familiar to all. However, Washington moves beyond these canonical examples by providing an overview of infections that possibly provoke specific mental disorders such as schizophrenia and anorexia. Toxoplasmosis is probably the most interesting pathogen that is known to alter behavior in rodents and, intriguingly, possibly behind the attraction to cat pee flavored wine.

While I am (and remain) a staunch defender of free will and do not believe that a microbe can determine behavior, Washington provides ample evidence of microbe-induced alterations in neural circuitry, brain neurochemistry, and hormonal balance and mental illness that can no longer be dismissed as mere coincidence. Perhaps many mental illnesses are varieties of encephalitis?