Epidemiological and Phylogenetic Analysis of Reassorted H10Nx Avian Influenza Viruses in Guangdong Province, China.

AIMS: H10 subtype avian influenza viruses circulate widely among wild and domestic birds worldwide. These viruses have crossed species barriers to infect mammals, including humans, with cases of H10N3, H10N5 and H10N8 reported. During active surveillance in Guangdong Province, China, between 2023 and 2025, we isolated 10 H10Nx influenza A viruses from wild birds and domestic ducks. To characterise their epidemiology and evolutionary dynamics, we analysed public sequence and surveillance data and found H10 viruses across all inhabited continents, including more than 400 isolates from China. METHODS: Bayesian phylogeographic analysis revealed that China is an important transmission hub for Eurasian-lineage H10 viruses. RESULTS: Phylogenetic analysis of the 10 H10 genes placed them within the North American lineage. Reassortment analysis indicated that these 10 isolates underwent complex gene exchange with multiple influenza A subtypes, resulting in five distinct genotypes. Some gene segments were identical to those found in avian H10N5 viruses that infect humans, indicating genetic relatedness to human-infected strains, likely resulting from reassortment events. Notably, these isolates harboured several amino acid substitutions associated with mammalian adaptation. Frequent transmission at the wild bird-poultry interface highlights potential zoonotic risks. CONCLUSIONS: Our findings highlight the importance of H10 viruses as a public health risk and the need for intensified active surveillance in wild birds and poultry.