Evolutionary dynamics of GII.17 norovirus

Area of Science:

• Virology
• Molecular Evolution
• Epidemiology

Background:

• Norovirus (NoV) genotype GII.17 increased in frequency during 2014-2015 outbreaks in East Asia, surpassing GII.4 strains.
• GII.17 genotype has been detected globally for over three decades.
• Understanding the evolutionary dynamics of GII.17 is crucial for tracking its spread and impact.

Purpose of the Study:

• To examine the evolutionary dynamics of norovirus (NoV) GII.17 over the past four decades.
• To identify key genetic changes contributing to the recent predominance of GII.17 strains.

Main Methods:

• Downloaded complete or nearly complete VP1 sequences of NoV GII.17 from GenBank.
• Conducted phylogenetic analyses using maximum likelihood and Bayesian Markov chain Monte Carlo methods.
• Analyzed amino acid variations in the P2 subdomain, including insertions, deletions, and epitope changes.

Main Results:

• Phylogenetic analysis divided GII.17 into four clades (A-D), with post-2012 outbreak strains in Clades C-D.
• Estimated nucleotide substitution rate at 1.68 × 10⁻³ per site per year, with the most recent common ancestor in 1840.
• Identified high variability in the P2 subdomain (44% amino acid variation) with insertions/deletions and alterations in epitopes A, B, and D.

Conclusions:

• Novel GII.17 strains causing outbreaks in 2013-2015 likely possess two new variants.
• Evolvement of the human histo-blood group antigen (HBGA) binding site and epitopes within the P2 subdomain may drive GII.17 predominance.
• These genetic adaptations could enhance viral fitness and regional outbreak potential.