Abstract
OBJECTIVES: Norovirus genotype GII.3[P12] strains have been an important pathogen for sporadic gastroenteritis infection. In previous studies of GII.3[P12], the number of specimens and time span are relatively small, which is difficult to truly reflect the infection and evolution of this type of norovirus. Here we report a molecular epidemiological study of the NoVs prevalent in Jiangsu between 2010 and 2019 to investigate the evolution of the GII.3[P12] strains in China. METHODS: In this study 60 GII.3[P12] norovirus strains were sequenced and analyzed for evolution, recombination, and selection pressure using bioanalysis software. RESULTS: The GII.3[P12] strains were continuously detected during the study period, which showed a high constituent ratio in males, in winter and among children aged 0-11 months, respectively. A time-scaled evolutionary tree showed that both GII.P12 RdRp and GII.3 VP1 sequences were grouped into three major clusters (Cluster I-III). Most GII.3[P12] strains were mainly located in sub-cluster (SC) II of Cluster III. A SimPlot analysis identified GII.3[P12] strain to be as an ORF1-intragenic recombinant of GII.4[P12] and GII.3[P21]. The RdRp genes of the GII.3[P12] showed a higher mean substitution rate than those of all GII.P12, while the VP1 genes of the GII.3[P12] showed a lower mean substitution rate than those of all GII.3. Alignment of the GII.3 capsid sequences revealed that three HBGA binding sites of all known GII.3 strains remained conserved, while several amino acid mutations in the predicted antibody binding sites were detected. The mutation at 385 was within predicted antibody binding regions, close to host attachment factor binding sites. Positive and negative selection sites were estimated. Two common positively selected sites (sites 385 and 406) were located on the surface of the protruding domain. Moreover, an amino acid substitution (aa204) was estimated to be near the active site of the RdRp protein. CONCLUSIONS: We conducted a comprehensive analysis on the epidemic and evolution of GII.3[P12] noroviruses and the results suggested that evolution was possibly driven by intergenic recombination and mutations in some key amino acid sites.