Enteric microbiota influences enteric viral infections, and host response to these pathogens and vaccines. Using gnotobiotic (Gn) pigs transplanted with human gut microbiota (HGM), we studied the effects of HGM on the immune response to oral rotavirus vaccination and rotaviral disease. We also used HGM transplanted Gn pigs to determine the effects of HGM on human norovirus infection. Despite commercially available vaccines, human rotavirus is a leading acute gastroenteritis in children, especially those in developing countries. Human norovirus (HuNoV) is a leading cause of acute gastroenteritis in all age groups worldwide, and no vaccines are commercially available. Further understanding of how enteric microbiota influences these viral diseases may identify therapeutic targets.

In our rotavirus study, pigs were colonized with HGM from an infant with low fecal concentrations of enteropathy biomarkers and responded well to their first dose of oral rotavirus vaccine (healthy human gut microbiota "HHGM"); or pigs were colonized with HGM from an infant with high fecal concentrations of enteropathy biomarkers and a poor response to the first dose of oral rotavirus vaccine (unhealthy human gut microbiota "UHGM"). HHGM colonized pigs had stronger cell-mediated and mucosal immune response to oral rotavirus vaccine compared to UHGM pigs based on the number of rotavirus-specific IFN-γ producing T cells in the ileum, spleen, and blood, and trends towards higher rotavirus specific antibody titers in intestinal contents, respectively. Significant correlations between multiple Operational Taxonomic Units (OTUs) of bacteria and frequencies of IFN-γ producing T cells at the time of human rotavirus challenge existed, suggesting that certain members of the microbiota influenced the immune response to the vaccine. After the vaccinated pigs were challenged with human rotavirus, HHGM pigs had less severe and shorter duration of viral shedding and diarrhea compared to UHGM pigs, suggesting that HHGM facilitated development of stronger protective immunity. These results demonstrated that composition of the enteric microbiota influenced host immune response to oral vaccination.

In the norovirus study, Gn pigs were colonized with HHGM to determine the effects of microbiota on HuNoV infection. Colonized pigs shed more virus for a longer duration than non-colonized pigs, and also had higher viral titers in the duodenum and distal ileum. Diarrhea was more severe 4-10 days post-infection and lasted longer in colonized compared to non-colonized pigs. Twenty-seven genes related to the immune system were highly upregulated in HuNoV infected, colonized pigs compared to non-colonized controls. These result showed that HHGM influenced infectivity of HuNoV in the Gn pig model and altered host gene expression related to the immune system.

These studies showed that HHGM can improve the host immune response and efficacy of rotavirus vaccine, but it can also enhance infection and clinical disease in HuNoV infected Gn pigs. Depending on the virus, gut microbiota may be beneficial or detrimental to the host. Those developing future treatments aimed at altering microbiota to prevent or ameliorate one viral pathogen need to consider the potential for enhancing a different pathogen. These studies demonstrated the usefulness of HGM transplanted Gn pigs for evaluation of microbiota influence on infection and immunity of enteric viral pathogens.