SARS-CoV-2 Interacts with Mucosal Dysbiosis to Cause the Wide Range of Disease Seen in Covid-19

Hypothesis: SARS-CoV-2 amplifies pre-existing dysbiosis induced mucosal inflammation and this can cause a severe systemic inflammatory disease. The microbial flora perturbation can persist long after the virus has been eliminated leading to a wide range of long Covid symptoms. Evidence: Dysbiosis induced mucosal inflammation increases with age and is strongly associated with the metabolic syndrome (obesity, type 2 diabetes mellitus, ischaemic heart disease, hypertension, and depression). These are risk factors for the conversion of mild to severe Covid-19. Certain common strains of Staphylococcus aureus, which is commonly carried in pharyngeal mucosa, can trigger a cytokine cascade as seen in severe Covid-19. Blood group A and vitamin D deficiency, which are risk factors for hospitalisation in Covid-19 are also associated with increased S. aureus pharyngeal carriage rates. Multi-inflammatory syndrome in children is a post Covid condition which resembles toxic shock syndrome and Kawasaki disease (the former is known to be caused by staphylococcal pyrogenic toxins). A number of studies have shown dysbiosis of the oral mucosa and rectal mucosa in patients who progress to severe Covid-19. The wide range of pathology seen during and following SARS-CoV-2 infection is more in keeping with dysbiosis induced inflammation (multiple pathogenic bacteria at multiple sites) than with an otherwise simple viral induced respiratory tract infection. Implication: Optimization of the microbial flora, prior to encountering the virus, could have reduced the severity of the pandemic. The consumption of fermented foods, especially yoghurt, holds the most promise for reducing dysbiosis induced mucosal inflammation and preventing a wide range of complications. Reduced mucosal inflammation brings not only health but also happiness in which oxytocin has a key role