To analyze the genetic evolution and molecular characteristics of the H5N6 avian influenza virus A/Changsha/1/2022(H5N6) in a human infection case in Changsha City, providing insights for the prevention and control of H5N6 avian influenza transmission to humans. Methods The sample underwent whole-genome sequencing on a thirdgeneration sequencing platform. Reference sequences were downloaded from the NCBI and GISAID databases for comparison.
The phylogenetic tree was constructed and key amino acid mutation sites were analyzed using MEGA7 software. Results The sequence analysis results revealed that the strain studied belongs to the H5 subtype Clade 2.3.4.4b branch. The PB1 gene shared 99.69% homology with the H5N6 virus A/duck/Hunan/S40199/2021(H5N6) from Hunan Province; PB2 had 98.58% homology with A/Whooper swan/Sanmenxia/Y36/2020(H5N8); and other sequences showed high homology with the strain A/Guangdong/1/2021(H5N6) discovered in Guangzhou in 2021. These results indicate that an infection with a recombinant H5N6 subtype avian influenza virus caused the case. The amino acid composition of the cleavage site was RERRRKR ↓ GLF, consistent with high-pathogenicity avian influenza characteristics. The HA sequence showed no mutations at the Q226L and G228S sites, indicating the preservation of characteristics binding to avian receptors. However, mutations at the S127P, S137A, T160A, T192R, and A267T sites increased the virus´s affinity for humans. A deletion found in positions 59-70 of the NA protein stalk implies enhanced viral virulence in mammals. Mutations were noted in the internal genes; S622G in PB1, K389R and V598T in PB2, N409S in PA, N30D and T215A in M1, and P42S in NS1, which may enhance the virulence of avian influenza virus in infecting mice. Conclusions The H5N6 virus strain detected in a human case in Changsha City in this study is highly pathogenic, prone to bind to avian receptors, but numerous mutations at key amino acid sites facilitate infection in humans. Continuous monitoring and research on H5N6 avian influenza virus should be strengthened.