Genetic and evolutionary characteristics of an avian influenza A (H5N8) virus isolated from migratory bird

  Objective  To analyze the genetic and evolutionary characteristics of an avian influenza A (H5N8)virus strain isolated from a dead swan at a migratory bird monitoring station in Feidong county of Anhui province.

  Methods  Virus RNA extraction was conducted by using the samples collected from the dead swan, and real-time fluorescence quantitative RT-PCR was used the subtyping of influenza virus. HA and NA gene sequencing after amplification of the positive samples were conducted by first-generation sequencing method. Bioinformatics software was used to construct phylogenetic evolutionary tree and analyze its molecular characteristics.

  Results  The nasal swab, beak swab and cloacal swab from the dead swan in Feidong, which were received on December 1, 2020, were all positive for H5 subtype by PCR. Sequencing results showed that the strains from three samples shared the same sequence of avian influenza A (H5N8) virus. Phylogenetic analysis showed that the virus belonged to 2.3.4.4 lineage and had high similarity with the isolates from Egypt and Russia. The HA and NA genes were in Eurasian lineage and had been adapted to different hosts. The HA cleavage site of the virus showed highly pathogenic molecular characteristics, carried 6 glycosylation sites and contained the amino acid mutations of S133L, S137A, T160A, D187N, K193N, Q196K and S227R. There were K389R and V589T mutations in PB2 protein, N409S mutations in PA protein, N30D and T215A mutations in M1 protein, S31N mutations in M2 protein, and P42S mutations in NS1 protein.

  Conclusion  The receptor binding site of avian influenza A (H5N8) virus isolated in this study was still avian origin receptor, but it had the molecular characteristics of human origin receptor. Mutations in other amino acid sites suggested the risk of increased virulence of avian influenza virus, and further surveillance is needed.