Analysis on genetic characteristics of HA gene of influenza A(H1N1)pdm09 viruses in Weifang city,Shandong province from 2013 to 2020
Objective To analyze the genetic evolution characteristics of the HA gene of A(H1N1)pdm09 influenza viru-ses in Weifang city,Shandong province from 2013 to 2020,and to understand the mutation of the A(H1N1)pdm09 sub-type,so as to provide scientific evidence for early detection of new variants and precise prevention and control.Methods From 2013 to 2020,positive samples of the A(H1N1)pdm09 influenza virus were collected in Weifang city,Shandong province,and virus isolation was subsequently performed.Over the years,18 strains of the virus were selected for next-generation sequencing to obtain their HA gene sequences.A phylogenetic tree was constructed using the Maximum Likeli-hood(ML)method with RAxML software,amino acid site variations were analyzed using BioEdit software,HA glycosy-lation sites were analyzed using the NetNGlyc 1.0 Server,and selective pressure analysis was performed using the Data-Monkey online software with Single Likelihood Ancestor Count(SLAC)model and Fixed Effects Likelihood(FEL)mod-el.Results The 18 A(H1N1)pdm09 isolates were categorized into subclades 6B,6B.1,and 6B.2.With nucleotide ho-mology greater than 97.3％,most strains(17/18)belonged to the same subclade as the corresponding vaccine strains of each year.Amino acid sequence analysis revealed 12 to 22 mutations per strain,including mutations in antigenic determi-nants such as L161I,S162N,K163Q,S164T in the Sa region;S185T,T185I in the Sb region;H138 Y,S203T in the Ca re-gion;and S74R in the Cb region.Approximately 83.3％of the viruses had 2 or more antigenic determinant muta-tions.Mutations Q223R in the receptor-binding 220-loop and nearby S183P and I216T were also observed.Frequent chan-ges in glycosylation sites began in 2016,including the loss of 11NSTD,addition of 162NQSY,and variations in 162NQTY.Selective pressure analysis showed dN/dS values of 0.65 and 0.279,with no positively selected sites identified.Conclusion From 2013 to 2020,the HA genes of A(H1N1)pdm09 influenza viruses in Weifang city were generally similar to those of the corresponding vaccine strains,but exhibited con-tinuous variation at the nucleotide and amino acid levels,thus necessitating enhanced surveillance.
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