What about the gut microbiota?
The gut microbiota is a mix of microorganisms (bacteria, viruses, fungi…) making up a complex environment that interacts with the viruses responsible for gastroenteritis. Since each individual has a unique microbial ecosystem, these interactions, as well as the nature and severity of the symptoms, vary from person to person.11.
No matter what virus is responsible, viral gastroenteritis leads to a decrease in diversity of species composing the gut microbiota and impacts the abundance of three species12 : Prevotella, Staphylococcus and Atopobium. The resulting imbalance (called “intestinal dysbiosis”) is the source of several symptoms observed in patients. For instance, abundant diarrhea that characterizes rotavirus-induced gastroenteritis is the result of disorganization of the microbiota that leads to the destruction of microbial barrier.
Is the gut microbiota a frenemy?
Dysbiosis alone cannot explain the whole story: for example, the norovirus can merge with “commensal” bacteria (i.e. beneficial and naturally present in the microbiota) or act together with “harmful” bacteria (pathogens) and cause inflammation. The body therefore produces natural antiviral substances, such as interferons. However, as a result of strong stimulation, these substances turn against the body and attack it, thus causing severe intestinal lesions. The underlying mechanisms ruling over the interactions between these agents are still poorly understood and are the subject of many research studies. But relations between norovirus and gut microbiota can also be beneficial: experiments in mice have shown that intestinal dysbiosis caused by antibiotics may prevent or mitigate norovirus infection.
The role of genetics
These findings give us an overview of the complex relations existing between viruses originating from our environment and microorganisms living in our intestines. In fact, they seem to depend on a third player: our genes. Based on studies carried out in rodents, we are not equal when it comes to fighting norovirus infections: there is an individual susceptibility which depends on our genetic makeup, our gut microbiota and the presence of concomitant infections, that leads to a great variety of symptoms and long-term effects.
11. Dinleyici EC et al. Time series analysis of the microbiota of children suffering from acute infectious diarrhea and their recovery after treatment. Front Microbiol. 2018 Jun 12
12. Chen SY, Tsai CN, et al. Intestinal microbiome in children with severe and complicated acute viral gastroenteritis. Sci. Rep. 7:46130.