Analysis of the characteristics of hemagglutinin and neuraminidase genes of influenza A/H1N1(09pdm) viruses isolated in Yancheng area in 2014-2017

Objective To analyze the genetic characteristics of the hemagglutinin(HA) and neuraminidase(NA) genes of the influenza A/H1N1(09pdm) viruses isolated in the city of Yancheng in 2014-2017. Methods The throat swab specimens of patients with influenza-like illness (ILI) from sentinel surveillance hospitals and outbreak sites were detected using the method of real time RT-PCR. The influenza A/H1N1(09pdm) viruses were isolated using MDCK cell culture method in 2014-2017. The strains in 2014-2017 were selected randomly and their sequences of the HA1 and NA genes were amplified through one step RT -PCR method and the PCR products were sequenced. The mutations of genes and acid locus were analyzed and the evolutional trees were generated using bioinformatics software. Results The clustering relationships of the respective branches of HA1 and NA genes of seventeen A/H1N1(09pdm) strains isolated in Yancheng area were basically the same and the phylogenetic trees of HA1 and NA genes were respectively clustered into four evolutionary branches. Compared with the vaccine strain A/California/07/2009(H1N1pdm)in the Northern Hemisphere, a total of three antigen epitopes (Ca, Sa, Sb) in HA1 genes of strains in Yancheng area were involved in six antigenic sites (K154R, S162N, K163Q, S185T, L191I, S203T); there were three mutations (D222G/N, G223R, E224K) in the 220 ring and one locus (L191I) in the 190 helix of the receptor binding sites; the two strains (A/Jiangsu-YC/SWL1540/2017, A/Jiangsu-YC/SWL1545/2017) isolated in 2017 increased the 162NQS glycosylation site. Because the strains of the antigen epitopes, receptor binding sites and glycosylation sites in the HA1 genes had a certain degree of variations in Yancheng area in 2014-2017, the protective effects of vaccine strain A/California/07/2009 (H1N1pdm) was limited at the gene level. The two strains (A/Jiangsu-YC/SWL1540/2017 and A/Jiangsu-YC/SWL1545/2017) isolated in 2017 were clustered with vaccine strain A/Michigan/45/2015(H1N1pdm) and had better protective effects. Seventeen A/H1N1(09pdm) strains had no mutations in catalytic residues and drug resistant sites of NA genes, but a part of strains had a certain degree of variations in glycosylation sites of NA genes. Conclusions These results indicated the HA1 and NA genes of influenza A/H1N1(09pdm) viruses circulated in Yancheng area in 2014-2017 changed gradually. The accumulation of these mutations would result in antigenic drift of influenza A/H1N1(09pdm) viruses. Key words: Influenza A/H1N1(09pdm) virus; RT-PCR; Hemagglutinin gene; Neuraminidase gene; Sequencing