Objective To analyze the genetic evolution and molecular characteristics of H5N8 avian influenza viruses (AIVs) isolated from the poultry in a live poultry market (LPM) in Urumqi, Xinjiang.

Methods Oropharyngeal and cloacal swabs of poultry were collected from a LPM in Urumqi in 2016. AIVs were isolated by inoculating swab samples into chicken embryos. Hemagglutination test and RT-PCR were used to identify the AIVs. The genes of isolated AIVs were amplified with the universal primers of AIV and whole-genome sequencing was also performed. Pairwise sequence alignment and analysis of phylogenetic and molecular characteristics were performed using BLAST, Clustal W, MEGA-X and DNAStar software.

Results Five H5N8 AIVs were isolated from poultry. These strains shared a nucleotide identity of 99.70%-100.00%, which indicated that they were from the same source, and were named XJ-H5N8/2016. Phylogenetic analysis based on hemagglutinin(HA), NS and PB2 genes showed that these isolates were clustered together with H5N8 AIVs isolated from the migratory swans in Hubei, Shanxi and Sanmenxia, and the ducks in India during 2016 to 2017. Moreover, they were also clustered together with H5N6 AIVs isolated from minks in China and the first case of human infection in Fujian. The phylogenetic tree of neuraminidase(NA) gene indicated the five isolates clustered together with H5N8 AIVs isolated from ducks in India in 2016, and the phylogenetic trees of PB1, MP, PA and NP genes showed that they were clustered together with H5N8 AIVs isolated from wild birds and poultry in Egypt, Cameroon, Uganda, Congo and other African countries in 2017. The HA cleavage sites of XJ-H5N8/2016 contained five consecutive basic amino acids, indicating high pathogenicity. Multiple mutations in the genes of XJ-H5N8/2016 could enhance its virulence and pathogenicity to mammals.

Conclusions The five strains of H5N8 AIVs isolated from the LPM were highly pathogenic and closely related to the H5N8 AIVs isolated from migratory birds and poultry in Hubei, Shanxi, Sanmenxia area, Africa and India during 2016 to 2017. Meanwhile, some of the viral genes were also closely related to the H5N6 AIVs isolated from the minks and human in China. Multiple mutations could increase the virulence and pathogenicity of AIVs to mammals, which could pose a potential threat to public health.