The relationship between disease and microbes was first proposed in the 17th century, but the basic standards for proving that infection causes disease were not laid down until 1883, when the German bacteriologists Robert Koch and Friedrich Loeffler provided the first evidence of the processes underlying germ theory.

While contemporary researchers across the globe continue to unearth the microbial origins of physical illnesses, a new theory on mental illness has quietly emerged, not without its share of controversy. Some researchers in the field are now estimating that infectious organisms cause from 10% to 75% of serious mental disorders. It is an unnerving supposition that otherwise healthy people can “catch” mental illness, one that National Book Circle Award winner Harriet A. Washington tackles in her new book, Infectious Madness.

Mental illness has long been the stepchild of medicine—a terrifying set of disease states that you can’t identify on a slide under a microscope. As a result of a change in direction, researchers are facing a possible paradigm shift that replaces psychosocial factors with biologic ones as the cause of a large portion of mental disorders.

Ms. Washington’s book, organized in seven thorough chapters, traces the growing incidence of microbial triggers of mental disease. She also questions the nature of proof, as opposed to mere correlation, and proposes that traditional mechanisms for establishing proof must be supplemented with modern tools and strategies. This is a well-researched book that upends the table on modern psychiatry and its honored pioneers. “By 2013, mental-illness researchers had largely abandoned Freud [to explore] neurophysiology,” writes the author.

Underlying Motive

In chapter 1, Ms. Washington examines the origin of the groundbreaking germ theory and how it bypassed mental illness. The writing is lively, and the medical history she unveils is very interesting. But the main point of chapter 1 is to set up the book’s underlying motive, which is to confront mainstream psychiatry’s franchise on mental illness and its unwillingness to entertain ideas that confront its orthodoxy. “Thus it is that even in our time, when most psychiatrists treat only with medication, the growing evidence that infection makes a strong contribution to mental illness is studiously avoided,” writes Ms. Washington. 

Americans are taking more prescription drugs for various psychiatric disorders than ever before. It is a multibillion-dollar industry, and researchers that challenge the psychiatric-Pharma partnership have their work cut out for them. Moreover, sea change in the scientific community sometimes happens at a glacial pace. It took nearly 3 decades to formally acknowledge that infection with Helicobacter pylori is the strongest known risk factor for gastric cancer, which is the second leading cause of cancer-related deaths worldwide.

In chapter 2, titled provocatively “The Fetus as Battleground,” Ms. ­Washington’s talent as a science writer is on display, making for a scintillating read. She poses the question: “Do pathogens sow the seeds of schizophrenia in the womb, and if so, how?” The author notes that many common pathogens, such as herpes, toxoplasma, and cytomegalovirus, release viruses that flood the fetus’s cerebral fluid and brain with proteins that can trigger an inflammatory response from the immune system.

Role of Inflammation

Gathering data from researchers, the author suggests that the naive immune system may attack healthy brain tissue instead of the invading pathogen. She links this to mental illness by pointing out that people with schizophrenia seem to suffer profound but indirect damage from inflammation created by their own immune system. She quotes French scientist Hervé Perron: “The neuron is discharging neurotransmitters, being excited by these inflammatory signals. This is when one develops hallucinations, delusions, paranoia, and hyper-suicidal tendencies.”

Given the role of inflammation in a host of diseases including cancer, this is fecund territory for exploration of its role in mental disease. However, a careful read of this chapter, some of which will challenge the lay reader’s science background, shows that much of this work is still in its infancy. But the author’s tenor throughout is positive.

She writes, “Determining the microbe’s specific nature will allow researchers to target it with the most effective medication, just as discovering that [human papillomavirus (HPV)] causes cervical cancer allowed scientists to develop a vaccine against this global killer.” True, but the road from discovery to developing a vaccine is long and arduous, as the HPV story demonstrated.

To that end, Ms. Washington spends the next chapter, called “Growing Pains,” describing the painstaking efforts in the laboratory, which take years if not decades to prove a scientific theory. And she acknowledges that acceptance of microbe-driven mental illness will be hard and slow.

There are some very entertaining anecdotes in “Growing Pains.” However, the last line of the chapter lets readers know that they are about to take some side trips off the main road. Ms. Washington writes, “We must consider how the infinite variety of pathogens can distort the very nature of society.” Tying microbes to mental illness has scientific grounding, but tying microscopic entities to the vagaries of human society is a bit of a stretch.

Worth the Read

One challenge for a writer taking on a controversial and relatively new scientific theory is gathering enough solid information to fill a book with interesting and provocative content. For the most part, Ms. Washington lives up to the task, but there are times when she veers off course into historical field trips that, while entertaining and thoughtful, can feel like filler. To her credit, due to her skillful and energetic writing, even those occasional forays are worth the read.

One challenge for a writer taking on a controversial and relatively new scientific theory is gathering enough solid information to fill a book with interesting and provocative content. For the most part, Ms. Washington lives up to the task….

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The book’s final chapter, “Tropical Madness,” is set in sub-Saharan Africa and documents, among other things, the associations between mental symptoms and a multitude of parasites. Correlating HIV with mental illness seems a bit of a stretch, but she makes a persuasive case. Mental illness is devastating, and it is still stigmatized, in part, because of its mysterious origin. If microbes do indeed have a prominent role in mental illness, as Ms. Washington’s fine book suggests with vigorous scientific backing, it could take the mystery out of mental illness and lead to a cure.

This book is recommended for readers of The ASCO Post. ■