Evolutionary dynamics of GII.17 norovirus.

Background: During the winter of 2014-2015, a rarely reported norovirus (NoV) genotype GII.17 was found to have increased its frequency in norovirus outbreaks in East Asia, surpassing the GII.4 NoV infections. GII.17 genotype has been detected for over three decades in the world. The aim of this study is to examine the evolutionary dynamics of GII.17 over the last four decades.

Methods: NoV GII.17 sequences with complete or nearly complete VP1 were downloaded from GenBank and the phylogenetic analyses were then conducted.

Results: The maximum likelihood analysis showed that GII.17 genotype could be divided into four different clades (Clades A-D). The strains detected after 2012, which could be the cause of the outbreaks, were separated into Clades C-D with their mean amino acid distance being 4.5%. Bayesian Markov chain Monte Carlo analyses indicated that the rate of nucleotide substitution per sites was 1.68 × 10-3 nucleotide substitutions/site/year and the time of the most recent common ancestor was 1840. The P2 subdomain of GII.17 was highly variable with 44% (56/128) amino acids variations including two insertions at positions 295-296 and one deletion at position 385 (Clades C and D) and one insertion at position 375 (Clade D). Variations existed in Epitopes A, B and D corresponding to GII.4 and human histo-blood group antigens binding site I in P2 subdomain.

Conclusion: The novel GII.17 strains that caused outbreaks in 2013-2015 may have two new variants. The evolvement of HBGAs binding site and epitopes in P2 subdomain might contribute to the novel GII.17 strains predominance in some regions.