Evolutionary analysis of hemagglutinin gene of influenza A(H1N1) pdm09 virus in Huairou district of Beijing, 2013−2018

Abstract

Objective To analyze the mutations in hemagglutinin (HA) gene of influenza A(H1N1)pdm09 virus in Huairou district from 2013 to 2018, so as to understand the characteristics of genetic evolution. Methods Forty-two strains of influenza that were positive by cell culture and were identified as influenza A(H1N1)pdm09 virus in Huairou district were selected from different periods of surveillance during 2013 to 2018. HA gene sequences were obtained by RT-PCR and sequencing. MEGA6.0 software was used to analyze the molecular characteristics of HA and to construct the phylogenetic tree. Results The average genetic distances of nucleotides in HA gene between influenza A(H1N1)pdm09 virus strains isolated in each year from 2013 to 2018 and vaccine strains A/California/07/2009 were 0.017, 0.020, 0.028, 0.027 and 0.033, respectively. The phylogenetic tree show that the influenza A(H1N1)pdm09 virus strains formed two main branches. The strains isolated from 2013 to 2015 aggregated to A/California/07/2009 while the strains from 2016-2018 aggregated to A/Michigan/ 45/2015 (6B.1). There were 10 mutations in HA antigenic sites, including S220T, P154S, H155Y, E252G, S91R, K180Q, S181T, S179N, S202T and A203V. Conclusions The HA gene of influenza A(H1N1)pdm09 virus strains in Huairou District from 2013 to 2018 was constantly mutating, and the distance to the vaccine strain in 2009 was gradually increasing. Increments of both mutation frequency of antigenic sites and genetic diversity indicated the importance of surveillance for the molecular characteristics of influenza virus. Key words: Influenza A(H1N1) pdm09 virus; Hemagglutinin; Molecular characteristics; Evolutionary analysis