COVID-19 and the Microbiome: The Gut-Lung Connection

The world is currently experiencing a major pandemic due to COVID-19, a disease caused by SARS-CoV-2 infection. This virus is highly transmissible and clinically presents with a wide range of manifestations. The microbiome has a profound effect on the development of host immunity and susceptibility to infection. In severe COVID-19 patients, alterations of the gut and lung microbiome were detected. Emerging evidence indicates bidirectional crosstalk through a gut-lung axis, in which microbial metabolites, such as short-chain fatty acids, play pivotal roles in human health. In this review we will discuss the gut and lung microbiome in health and during viral infection, with a focus on SARS-CoV-2 infection.