A researcher from Stony Brook University in New York has proposed a radical theory on what causes depression. According to Dr. Turhan Canli’s recently published paper, the behavioral and emotional changes we view as depression may actually be the side effects of a yet-to-be identified infection. Canli isn’t the first to put forward this suggestion and, if proven true, it could potentially change not only the way we view depression, but also the way we treat it.

Is Depression An Infectious Disease?

Scientists understand what depression is — it’s an emotional disease tied to the brain — and scientists understand what depression does. They have even observed the neurological makeup of depressed patients, confirming they are indeed different from the makeup of otherwise healthy individuals. Still, despite many years of expensive research on the condition, scientists still do not know the exact cause of depression. Sure, they believe there are environmental as well as genetic factors, but a clear-cut root has remained elusive. It may be that depression is caused by a complex combination of factors and a single cause does not exist. However, according to Canli, there may be a more simple answer: We just aren’t looking in the right place.

“Future research should conduct a concerted effort search of parasites, bacteria, or viruses that may play a causal role in the etiology of MDD (major depressive disorder),” Canli explained in a press release. Canli even went one step further adding, “I propose reconceptualizing the condition as some form of infectious disease.”

In his TedTalk on the subject, Canli explains how an infection may explain the underlying mechanism that leads to neurological imbalances that then lead to structural changes. The researcher contends there is already a plethora of evidence supporting his theory.

“The biggest clue is that depression is often associated with inflammation,” Canli told The Huffington Post. “The field overall is accepting of the notion that inflammation may play a role in depression, but the idea that [depression] could actually be something very specific that comes from parasites or bacteria or viruses — that's still new.”

Although at this point Canli does not have the funding to further investigate this theory, he did tell Medical Daily in an email how one would go about finding the infection that may cause depression.

“A key strategy will be to use molecular techniques such as genome sequencing to discover the presence of known and novel infectious agents in depressed patients (compared to healthy controls),” he said.

Link Between Inflammation And Depression

Inflammation is the body’s natural response to infection, but it is also seen as a reaction to stress and emotional issues, Discover Magazine reported. Inflammation’s link to depression is not completely understood, with doctors struggling to understand if depression causes inflammation or if it's actually the other way around.

"I believe there is a subgroup of depressed patients whose increased inflammation is causing their disease. But these ideas remain theories," Dr. Andrew H. Miller, a professor of psychiatry and behavioral sciences at Emory University, who is also investigating inflammation’s link to depression, explained to Prevention.

According to Canli, the idea that an outside pathogen could cause emotional changes, such as those observed in the depressed, is not that far-fetched. There have been a handful of reported cases where intestinal bacteria led to mood changes in both animal and human subjects.

“So, there's a possibility that these bacteria that we have in our guts may not only help us digest our food, but may also play a role in our emotional well-being,” Canli told Buzzfeed. “You could flip that upside down and say, well there's good bacteria, but maybe there's also bad bacteria that instead of lifting your mood could depress your mood…”

Canli hopes his paper will lead to large-scale studies that treat depression as an infectious disease rather than a mental health condition — something that he hopes could lead to more effective treatment of the widespread condition. If this theory turns out to be fact, it means the identification of microorganism biomarkers in a blood test could both diagnose depression and treat it accordingly.

Source: Canli T. Reconceptualizing major depressive disorder as an infectious disease. Biology of Mood & Anxiety Disorders. 2014.