Microbiological bases of obsessive‑compulsive disorder - the role of viruses, bacteria, and parasites in the onset and progression of OCD.

Obsessive‑compulsive disorder (OCD) is a current topic of discussion nowadays. OCD presents a variety of different etiologies including environmental, viral, cognitive, or genetic aspects. In this article, we focused on the possible correlation between various infectious diseases as well as generally the relationship between viruses, bacteria, and parasites, and an increased OCD risk. In this narrative review, we analyzed different types of articles found on PubMed, Google Scholar, and Scopus, as well as the articles of the National Institute of Mental Health. Searching criteria included articles from 1991 till the end of November, research involving human and animal patients (including monkeys and rats), and research published in English. Research showed a relationship between Herpes simplex virus, Rubella virus, Human immunodeficiency virus, Borna disease virus, Mycoplasma pneumoniae, Toxoplasma gondii, streptococcal infections, as well as gut microbiota and increased OCD risk. The possible mechanisms of this relation include neuroinflammation, brain tissue damage, autoimmune processes, and impairments in neurotransmitter levels. Infections caused by Varicella zoster virus, Measles virus, Mumps virus, Epstein‑Barr virus, Cytomegalovirus, or Borrelia Burgdorferi may also contribute to the increased risk of OCD. Reports showed an increased frequency of OCD occurrence in a group of infected people compared to a healthy group. However, there is no evidence of the influence of Influenza virus, Coxsackie virus, Poliovirus, Parvovirus B19, Enterovirus 71, West Nile virus, Treponema Pallidum, or Toxocara infections on the OCD risk. There is a significant relationship between various infectious diseases and an increased OCD risk. However, further studies are crucial to discover the exact pathomechanisms of these correlations and the potential influence of other pathogens on the onset of OCD.