ABSTRACT
@#Abstract: Objective To investigate the molecular characteristics of the H9N2 avian influenza virus (AIV) causing human infection in Yunnan Province in 2019, and to provide the scientific basis for the prevention and control of avian influenza in Yunnan Province. Methods Influenza virus typing was performed by real-time RT-PCR in two influenza-like illness samples, and the Illumina Miseq high-throughput sequencer was used to determine the viral genome sequence. HA and NA gene sequence alignment and phylogenetic tree construction were performed using Mega7.0 software. Results Real-time RT-PCR results showed that two influenza-like illness samples were positive for H9N2 subtype. The full length of HA and NA were obtained by genomic sequencing. Sequence system evolution analysis showed that the HA and NA of the two AIVs in Yunnan Province were in the same evolutionary clade as A/Chicken/Zhejiang/HJ/2007 and belonged to the G57 type. The HA nucleotide and amino acid homology of the two AIVs were 93.92% and 95.00%, respectively, and the NA nucleotide and amino acid homology was 93.31% and 82.03%, respectively. The nucleotide (amino acid) homology of HA was 92.29%-96.94% (93.77%-98.43%) and 92.84%-94.92% (94.18%-96.23%), respectively, and NA nucleotide homology (amino acid) were 91.81%-97.60% (77.82%-94.83%), 94.38%-97.22% (85.47%-94.55%), respectively, compared with that of human infected H9N2 epidemic strains obtained in China from 2015 to 2020. Both AIVs HA protein cleavage site sequences were PSRSSR↓GLF, which was in line with the characteristics of low pathogenic influenza. The analysis of HA protein receptor binding site showed that amino acids at positions 109, 161, 163, 191, 202, 203 and 234 were consistent with the reference strains, while amino acids at position 198 were mutated to T. N166D and 168N mutations were also found in HA protein, and both AIVs had 7 potential glycosylation sites. Analysis of the erythrocyte binding site of NA gene found that there were amino acid mutations at positions 369, 402, 403, and 432, and amino acid deletion at positions 63-65 was found in the NA genes. There were 4 and 5 potential glycosylation sites in the two AIVs, respectively, and no drug resistance site mutations were found. Conclusions The receptor binding sites, erythrocyte binding sites and glycosylation sites of HA and NA genes of H9N2 AIV in Yunnan Province have different degrees of variation, and monitoring and prevention and control should be strengthened.