Back to the Future: The Role of Infections in Psychopathology. Focus on OCD.

Objective: Recently, there has been a resurgence of interest in the relationship between infections and psychopathology, given the increasing data on the neurotropism and neurological/psychiatric morbidity of the SARS-COV2 virus, responsible for the current worldwide pandemic. Although the majority of observations were those obtained in mood and schizophrenic disorders, a few data are also available on the presence of bacterial or viral infections in patients suffering from obsessive-compulsive disorder (OCD). Therefore, given the limited information, the present paper aimed at reviewing the most updated evidence of infections in neuropsychiatric disorders and their possible mechanisms of actions, with a narrow focus on microbes in OCD. Method: This paper is a narrative review. The databases of PubMed, Scopus, Embase, PsycINFO and Google Scholar were accessed to research and collect English language papers published between 1 January 1980 and 31 December 2021. The data on PANDAS/PANS and those observed during severe brain infections were excluded. Results: Several pathogens have been associated with an increased risk to develop a broad spectrum of neuropsychiatric conditions, such as schizophrenia, mood disorders, autism, attention-deficit/hyperactivity disorder, anorexia nervosa, and post-traumatic stress disorder. Some evidence supported a possible role of infections also in the pathophysiology of OCD. Infections from Herpes simplex virus 1, Borna disease virus, Group A-Beta Hemolytic Streptococcus, Borrelia spp., and Toxoplasma gondii were actually found in patients with OCD. Although different mechanisms have been hypothesized, all would converge to trigger functional/structural alterations of specific circuits or immune processes, with cascade dysfunctions of several other systems. Conclusions: Based on the current evidence, a possible contribution of different types of microbes has been proposed for different neuropsychiatric disorders including OCD. However, the currently available literature is meager and heterogeneous in terms of sample characteristics and methods used. Therefore, further studies are needed to better understand the impact of infectious agents in neuropsychiatric disorders. Our opinion is that deeper insights in this field might contribute to a better definition of biological underpinnings of specific clinical pictures, as well as to promote psychiatric precision medicine, with treatments based on altered pathological pathways of single patients. This might be particularly relevant in OCD, a disorder with a high proportion of patients who are resistant or do not respond to conventional therapeutic strategies.