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Depression: A Non-Contagious Infectious Disease?

February 18, 2015

Some scientists are trying to solve the puzzle of depression by thinking outside the box. Turhan Canli, for instance, suggests that depression may be a non-contagious, infectious disease.

Canli, of Stony Brook University in New York, wonders whether an unknown pathogen(s) is the primary cause of depression. As pathogens do, it would trigger an inflammatory response by the immune system to ward off the infection. So, treating the inflammatory response will bring symptom relief but not eliminate depression’s cause.

A pathogen causing MDD, or major depressive disorder, would specifically target the nervous system. An individual carrying the pathogen may have no symptoms until the pathogen is activated by another factor, such as a stressful life circumstance. This same mechanism could also be responsible for other mental health disorders such a bipolar disorder, or PTSD.

Why Infection Makes Sense

Making a case for depression being an infectious disease rests on several biology-based arguments.

  1. People who have MDD act physically ill. They have trouble getting out of bed, have low energy, lose interest in activities, and the world. Canli also points out the individuals not steeped in Western medicine traditions report mostly somatic (physical) symptoms when they are depressed, instead of affective (emotion, mood) symptoms.
  2. Research has associated depression with inflammation of the brain tissue. Inflammation is an indicator of an immune response to a pathogen. A pathogen can be a parasite, bacterium, or a virus. Nature provides many examples of these pathogens causing changes in the emotional behavior of complex organisms.
  3. Scientists’ search for specific depression causing genes has not been successful. This search has been done on the human genes within our system, but eight percent of our human genome is based on chains of retroviruses. It is possible that depression causing retrovirus sequences could be triggered by stressful events.
  4. The human body is a repository for countless undetected bacteria and viruses that can be passed from parents to their children.

Turhan Canli is not alone in suggesting that depression may be an infectious disease.

Not A Psychiatric Condition

A clinical psychologist at the University of California, George Slavich, has been researching depression for years.

“I don’t even talk about it [depression] as a psychiatric condition any more,” said Slavich. “It does involve psychology, but it also involves equal parts of biology and physical health.”

Like Canli, Slavich points out that people feel miserable when they have an infectious disease. They get bored, fatigued, irritable, and just want to lie on the couch. This also describes many people with depression, and suggests there may be a common cause. Slavich sees inflammation as a sign that the immune system is fighting an infectious intruder.

Other scientists are skeptical of the pathogen-depression connection since the inflammation associated with depression can also be triggered by a fatty, sugary diet, obesity, and even loneliness. Still, the arguments for depression being an infectious illness are compelling, and scientists such as Canli hope for extensive research into this possibility.

Sources: Biology of Mood and Anxiety Disorders; The Guardian

Also published on Psyweb

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