Sequence analysis of Hemagglutinin of influenza A(H1N1)pdm09 viruses in Tangshan

Objective To analyze the evolutionary characteristics' of hemagglutinin (HA) gene of pandemic influenza A (H1N1) pdm09 virus isolated from Tangshan city during influenza seasons druing 2010-2016. Methods A total of 24 influenza A(H1N1)pdm09 virus strains isolated from patients with influenza-like illness (ILI) in 3 sentinel hospitals in Tangshan were selected, and the full-length sequences of HA gene were obtained. The bioinformatical and statistical softwares were applied to align and to analyze all the sequences. Results Compared with the vaccine strain A/California/7/2009, the HA genes of 24 A (H1N1) pdm09 strains showed 97.0%-99.0% nucleotide identity and 97.0%-98.5% amino acid sequence identity. Phylogenetic analysis showed all the 24 A (H1N1) pdm09 strains fell into HA genetic clades 1, 7, 6C, 6B, 6B1, and 6B.2, respectively. Amino acid analysis of the isolates revealed the presence of 8-16 changes in HA gene compared to the vaccine strain, seven of which occurred in three antigenic sites: H138Q/Y and S203T in Ca; N125S, K153E, S162N and K163T/Q in Sa; and S185T in Sb. The S162N substitution, specific to subclade 6B.1, generated a new potential N-glycosylation motif within the Sa antigenic site. Conclusions Compared to vaccine strain, the genetic drift of the Tangshan influenza A(H1N1) pdm09 viruses in Tangshan occurred as time went on, we should pay attention to the changes of epidemic strains in 6B branch. Key words: Influenza A (H1N1) pdm09 virus; Haemagglutinin; Sequence analysis; Phylogenetic tree