Depression is associated with cytomegalovirus and West Nile virus, and the protozoan parasite Toxoplasma gondii. It is thought that depression may be precipitated by the effect of immune signals (such as pro-inflammatory cytokines) reaching the brain from infections located in the peripheries of the body.Major depressive disorder is associated with bornavirus, as well as Bartonella and Borrelia species bacteria.Seasonal affective disorder is associated with Epstein-Barr virus.
