Norovirus: A Friendly Virus?

Many Stanford students can remember the norovirus outbreak that struck our campus last year.  First it was FloMo hall, then it was Theta house, and then the freshman dorms were hit.  Before we knew it single handicapped bathrooms were devoted to students suffering from the telltale signs, diarrhea and vomiting, and individual meals were prepackaged at the dining halls.  Although most people see this non-enveloped single-stranded RNA virus, in the family Caliciviridae, as the bad guy, could there be a beneficial role for norovirus in our lives?

A small percent of the bacteria in our bodies is harmful. The remaining bacteria are largely beneficial, and a substantial portion of these bacteria resides in our gastrointestinal tract performing a multitude of functions keeping us healthy.  This population of bacteria is included in our microbiome.  Recent studies suggest that there is an equally important microvirome that performs similar functions in our bodies.  A recent experiment aimed to evaluate the effects that Murine Norovirus (MNV) infection had on germ-free and antibiotic treated mice. The results showed the MNV infection preserved normal GI morphology and immune system conditions without causing symptoms in the mice.  Germ-free mice were used to see whether or not MNV could mimic the functions of bacteria.  Persistent MNV infection in these germ-free mice showed the restoration of normal intestinal physiology as well as increased immune response measured by T cell count, lymphocyte differentiation, and interferon expression.  These observations were recorded across several populations of germ-free mice and provided sufficient evidence that MNV could mimic the effect of commensal bacteria in the gut.
The study also looked at MNV infections in mice being treated with antibiotics.  This was a population of concern because many people being treated with antibiotics often suffer from vomiting, diarrhea, and abdominal cramps due to the elimination of gut bacteria.  Mice were treated for 2 weeks with antibiotics and had the same abnormalities as germ free mice.  After the 10^th day of infection in these antibiotic treated mice, the villus width increased, T cell count increased, Paneth cell granules increased (the main cell type in the epithelium of the small intestines), and interferon expression in T cells increased.  Basically infection with MNV could prevent the unwanted side effects of antibiotic use.

Although this study focuses on mice, it is easy to see how this research applies to humans.  While Stanford students automatically think of ground zero FloMo when they hear the word “norovirus”, maybe we should think about all the friendly bacteria in our stomachs and how norovirus could become a friendly virus. 


-Nalani Wakinekona 

References

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13960.html