Abstract: Based on the detection of H9 subtype avian influenza in 57 chicken farms in Yunnan province from January to June 2019,two H9 subtype avian influenza positive samples from Shilin and Chuxiong were selected for virus isolation.Total RNA was extracted from the isolated embryonic allantoic fluid of H9N2 subtype avian influenza virus,and HA and NA genes were amplified by RT-PCR with specific primers.The PCR products were purified and sequenced.Sequence alignment and phylogenetic analysis showed that the nucleotide sequence homology of HA and NA genes for two H9N2 of Yunnan strain in 2019 was 94.2% and 93.6%,respectively.Phylogenetic analysis showed that HA and NA genes of Yunnan H9N2 subtype avian influenza virus in 2019 belonged to ADKHKY28097 branch (Y280-like) of Eurasian lineage.The homology of HA gene of ACKYN12019 and ACKYN72019 was 94.3%,and the highest homology with the reference strain ACKJX2448 was 95.6% to 98.5%,the low homology with the popular H9N2 representative strains and vaccine strains in China.The cleavage site of HA protein 333-340 was PSRSSR↓GLF,which had the molecular characteristics of low pathogenicity avian influenza virus.The receptor binding sites all had mutations of E198T and Q234L,and had the characteristics of human receptor binding.There were 6 glycosylation sites at 29,141,298,305,313 and 492 amino acids.The homology of NA gene of ACKYN12019 and ACKYN72019 was 93.6%,and the homology with the representative strain of Y280-like were 97.1% to 97.5% and 93.7% to 94.6%,respectively.There were 6 potential glycosylation sites at 44,69,86,146,200 and 234 amino acids deleted in NA protein,and 368-369,399-403 were found by analysis of RBC binding sites of NA protein.There were variations in amino acids at position 432.The results showed that H9N2 subtype avian influenza virus had been mutating continuously,so its monitoring and control should be strengthened.

Key words: H9N2 avian influenza virus; hemagglutinin (HA) gene; neuraminidase (NA) gene; molecular characteristics