Characteristics of highly pathogenic avian influenza A (H5) viruses in clade 2.3.4.4b in China, 2010−2023

Objective Based on the global spread of highly pathogenic avian influenza A (H5) viruses in clade 2.3.4.4b, this study analyzed the transmission and phylogenetic evolution characteristics of the clade 2.3.4.4b viruses in China.

Methods The hemagglutinin （HA） gene sequences of H5 subtype clade 2.3.4.4b viruses were collected from Global Initiative of Sharing All Influenza Database. Combined with metadata such as host source, sampling time and geographical distribution of the viruses, a phylogenetic tree was constructed based on the maximum likelihood method, and the transmission path was inferred by phylogeography method to analyze the host source, temporal and spatial transmission and genetic evolution characteristics of H5 subtype clade 2.3.4.4b viruses in China from 2010 to 2023.

Results H5N1, H5N6 and H5N8 subtypes avian influenza viruses spread in wild waterfowl and poultry in China with different host sources. H5N1 and H5N8 viruses were mainly from wild waterfowl, and H5N6 viruses were mainly from poultry. Phylogenetic analysis showed that clade 2.3.4.4b viruses formed three obvious clusters （I, Ⅱ, Ⅲ） according to the evolutionary time, which were consistent with the trends of three global epidemics. Phylogenetic geographic analysis showed that the transmission and evolution of H5 subtype clade 2.3.4.4b viruses originated from central China.

Conclusion  Influenza A(H5) viruses in clade 2.3.4.4b continue to spread in China, and there is a high risk for virus importation through wild bird migration and poultry trade. All-round avian influenza surveillance and early warning in people, poultry and wild waterfowl should be continued. This study provided evidence for the risk assessment of H5 subtype avian influenza virus in China.