Could depression be caused by an infectious agent?

The gut-brain axis:
Emerging evidence in health and disease

'Absence of evidence' is not the same as 'evidence of absence'. No reliable evidence has been found to show that depression is caused by an infectious disease, but that might be because we've not searched for an infectious agent (a parasite, bacterium, or virus) before, says NHS Choices.

"Instead of conceptualizing Major Depressive Disorder (MDD) as an emotional disorder, Turhan Canli suggests to reconceptualize it as some form of an infectious disease."

"I suggest that some unknown pathogen(s) could play a causal role, and that the immune response is secondary to the infection; interventions that only target the immune response may bring symptom relief but would not address the root cause of the illness."

Inflammatory markers of infectious disease in depressive patients have been found (Interleukin (IL)-6, tumour necrosis factor alpha (TNF-alpha) and soluble interleukin-2 receptors (sIL-2R)).

"I think it would be worthwhile to conduct large-scale studies of carefully characterized depressed patients and healthy controls, using gold-standard clinical and infectious disease-related study protocols, as have already been developed for bacteria and viruses. Such efforts, if successful, would represent the ‘end of the beginning’, as any such discovery would represent the first step toward developing a vaccination for major depression."

NHS Choices report findings of a peer-reviewed journal. More....

Links To The Headlines

Could depression be an INFECTIOUS DISEASE? Condition is caused by parasites, bacteria or virus and could be prevented with a jab, expert claims. Mail Online, November 27 2014

What If We're Wrong About Depression? New York Times, November 26 2014

Links To Science

Canli T. Reconceptualizing major depressive disorder as an infectious disease. Biology of Mood and Anxiety Disorders. Published online October 21 2014