Abstract
From January 2015 to December 2018, 213 norovirus outbreaks with 3,951 patients were reported in Jiangsu, China. Based on viral RdRp and VP1 genes, eight genotypes, GII.2[P16] (144, 67.6%), GII.3[P12] (21, 9.9%), GII.6[P7] (5, 2.3%), GII.14[P7] (4, 1.9%), GII.4 Sydney[P31] (3, 1.4%), GII.1[P33] (1, 0.5%), GII.2[P2] (3, 1.4%), and GII.17[P17] (16, 7.5%) were identified throughout the study period. These genotypes were further regrouped as GII.R (Recombinant) and GII.Non-R (Non-recombinant) strains. In this report we showed that GII.R strains were responsible for at least 178 (83.6%) of 213 norovirus-positive outbreaks with a peak in 2017 and 2018. Most norovirus outbreaks occurred in primary schools and 94 of 109 (86.2%) outbreaks in primary schools were caused by GII.R, while GII.Non-R and GII.NT (not typed) strains accounted for 6 (5.5%) and 9 (8.3%) norovirus outbreaks, respectively. The SimPlot analysis showed recombination breakpoints near the ORF1/2 junction for all six recombinant strains. The recombination breakpoints were detected at positions varying from nucleotides 5009 to 5111, localized in the ORF1 region for four strains (GII.2[P16], GII.3[P12], GII.6[P7], and GII.14[P7]) and in the ORF2 region for the other (GII.4 Sydney[P31] and GII.1[P33]). We identified four clusters, Cluster I through IV, in the GII.P7 RdRp gene by phylogenetic analysis and the GII.14[P7] variants reported here belonged to Cluster IV in the RdRp tree. The HBGA binding site of all known GII.14 strains remained conserved with several point mutations found in the predicted conformational epitopes. In conclusion, gastroenteritis outbreaks caused by noroviruses increased rapidly in the last years and these viruses were classified into eight genotypes. Emerging recombinant noroviral strains have become a major concern and challenge to public health.
Highlights
The epidemiology of norovirus is strongly influenced by norovirus evolution through recombination or accumulation of mutations[7]
Our analysis showed that recombinant strains increased significantly in norovirus outbreaks between 2015 and 2018 and the GII.2[P16] recombinant strains were responsible for most outbreaks
A total of 213 norovirus outbreaks with 3,951 patients were reported to the Jiangsu Center for Disease Control and Prevention (CDC) from January 2015 to December 2018
Summary
The epidemiology of norovirus is strongly influenced by norovirus evolution through recombination or accumulation of mutations[7]. Recombination often occurs at the ORF1/ORF2 junction that leads to new combinations of capsid and RdRp types, further increasing genetic diversity[8]. These new recombinant strains might have increased fitness and transmissibility over their parental strains[9]. The same capsid genotype can be associated with different RdRp genotypes, which may offer a temporary selective advantage through altering the efficiency of virus replication[2]. To better understand epidemiologic and genotypic trends of evolving norovirus recombinant strains in the field, we examined and analyzed norovirus outbreak data and strains collected between January
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