Infectious Diseases may Cause Major Depressive Disorder

By: Marianna Catege

Depression may actually be infectious, according to Dr. Turhan Canli, the Associate Professor of Psychology and Radiology at Stony Brook University. His claim puts Major Depressive Disorder (MDD) in a new light, one that suggests it can be caused by parasitc bacterial or viral infections. In this highly prevalent disease, with roughly 7 percent of the U.S. population developing MDD, symptoms can include fatigue and other inflammatory biomarkers, which suggest an infectious origin (1). This may finally provide an explanation for MDD, a disease which previously had no clearly defined cause. Canli’s findings are published in Biology of Mood and Anxiety Disorders in November 2014.

Dr. Canli explains that patients affected by parasites, bacteria, and viruses often display changes in their emotional behavior similar to the changes caused by MDD. He further states that the human body is an ecosystem for these kinds of microorganisms, which we know are capable of affecting human gene expression. Thus, it is highly probable that microorganisms can cause MDD, a disease also associated with an interference in various genetic factors.

Based on the correlations Dr. Canli has observed between MDD and infectious agents, more research on the topic is warranted. As he states, “Future research should conduct a concerted effort search of parasites, bacteria, or viruses that may play a causal role in the etiology of MDD” (2).


  1. Kessler RC, et al. Prevalence, severity, and comorbidity of 12-month DSM-IV disorders in the National Comorbidity Survey Replication. Gen Psychiatry. 62. 617-627. (2005).
  2. Could Depression Actually Be a Form of infectious Disease? 2014. Stony Brook Newsroom.
  3. Lohoff, F. 2011. Overview of the Genetics of Major Depressive Disorder. PMC.