Molecular Evolution of Human Norovirus GII.2 Clusters

Xingguang Li,Erik M Volz,Sergei L Kosakovsky Pond,Haizhou Liu,Brittany Rife Magalis

doi:10.3389/fmicb.2021.655567

Abstract

BackgroundThe human norovirus GII.2 outbreak during the 2016–2017 winter season was of unprecedented scale and geographic distribution.MethodsWe analyzed 519 complete VP1 gene sequences of the human norovirus GII.2 genotype sampled during the 2016–2017 winter season, as well as prior (dating back to 1976) from 7 countries. Phylodynamic analyses of these sequences were performed using maximum likelihood and Bayesian statistical frameworks in order to estimate viral evolutionary and population dynamics associated with the outbreak.ResultsOur results revealed an increase in the genetic diversity of human norovirus GII.2 during the recent Asian outbreak and diversification was characterized by at least eight distinct clusters. Bayesian estimation of viral population dynamics revealed a highly fluctuating effective population size, increasing in frequency during the past 15 years.ConclusionDespite an increasing viral diversity, we found no evidence of an elevated evolutionary rate or significant selection pressure in human norovirus GII.2, indicating viral evolutionary adaptation was not responsible for the volatility of or spread of the virus during this time.

Highlights

Human norovirus (HuNoV) is a pathogenic agent that contributes substantially to the global burden of sporadic cases and outbreaks of acute gastroenteritis across all settings and age groups in humans (Ahmed et al, 2014)
Our findings suggest that close monitoring of the global spread of this emergent GII.2 strains is necessary for the prevention and mitigation of HuNoV acute gastroenteritis outbreaks
The results suggested that the evolutionary dynamics of the VP1 gene of HuNoV GII.2 strains in this data set were influenced largely by natural evolutionary forces, rather than adaptation to selective pressure from the host immune system, which was consistent with the previous study (Tohma et al, 2017)

Summary

Introduction

Human norovirus (HuNoV) is a pathogenic agent that contributes substantially to the global burden of sporadic cases and outbreaks of acute gastroenteritis across all settings and age groups in humans (Ahmed et al, 2014). HuNoV is classified into at least 10 genogroups (GI–GX) and 48 genotypes, based on phylogenetic analyses of the capsid gene (Zheng et al, 2006; Vinje, 2015; Chhabra et al, 2019, 2020). Among these different genogroups, genotypes belonging to the GI, GII, and GIV are primarily responsible for the acute gastroenteritis cases in humans (Kroneman et al, 2013; Vinje, 2015). The human norovirus GII. outbreak during the 2016–2017 winter season was of unprecedented scale and geographic distribution

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Conclusion