Virology and Microbiology

Norovirus (NoV) is responsible for most cases of pandemic and sporadic non-bacterial gastroenteritis outbreaks worldwide. Chronic infections have been described recently and will become more prevalent with increasing numbers of immunocompromised patients. Here, we studied the longitudinally genetic variability leading to immune escape and development of new quasi-species in chronically infected patients. To this aim, a quantitative ELISA was developed to measure NoV-specific IgG level chronically infected patients at different time points after infection. Evolution of NoV capsid gene was then assessed by next-generation sequencing (NGS), molecular dynamic analysis (SASA, RMSD, RMSF, and Radius of gyration) and structural modeling in a total of 20 samples from 5 chronically infected patients. Consensus sequences of all samples were used for genotyping and multiple sequence alignment. Quasi-species was reconstructed with assembly tool. NoV-specific IgG level increased over time, however in one of the patients decreasing the level of antibody was detected 6 months post-infection indicating immune escape of the virus. Alignment analysis revealed several mutations in the capsid gene, especially in the p domain leading to changes in accessibility and confirmation of the B-cell epitopes. A number of reconstructed quasi-species was found to be increased at the onset of infection and decreased after a certain period in chronically infected patients which leads to cure. In conclusion, the present study showed the fast evolution of NoV capsid gene in chronically infected patients leading to structural change and generation of new quasi-species.