The role of peripheral serotonin in SARS-CoV-2 infectivity, COVID-19 treatment and long COVID.

Gastrointestinal symptoms have emerged as a common, but underappreciated, cause of morbidity in relation to SARS-CoV-2 infection and the COVID-19 pandemic. This manifests as a range of indications including diarrhea, anorexia, nausea, vomiting and abdominal pain. In addition, the gastrointestinal tract may represent a route of viral entry via the epithelial cell layer lining the gut wall. This route of entry could be a significant component of disease pathogenesis, including effects on the nervous system via the gut-brain axis. In this review, we provide an assessment of the effects of COVID-19 on the gastrointestinal system, its involvement in disease severity and potential pathways for viral entry and infection in the gastrointestinal tract. We also examine evidence that gut-derived serotonin is affected by SARS-CoV-2 infection, how this may link to symptoms and disease pathogenesis and the potential link to the efficacy of selective serotonin reuptake inhibitors in reducing COVID-19 severity.