Intensive reassortment and frequent intercontinental transmission revealed by long-term genetic analysis of H10 avian influenza viruses in Taiwan

H10 subtype avian influenza viruses primarily circulate among wild waterfowl but can occasionally infect mammals, including humans, and recent sporadic human cases have raised significant public health concerns. In this study, we sequenced and analysed 59 H10 subtype viruses isolated from wild birds in Taiwan. Results showed that all isolates were genetically distinct from human and other mammalian H10 subtype isolates. Taiwanese isolates exhibited high genetic diversity and could be categorized into 34 distinct genotypes, with each genotype circulating only in a single migratory season and not recurring during subsequent seasons. Additional analyses revealed that certain gene pools frequently circulate in the Pacific Rim, with evidence of North American lineage genes establishing long-term populations in Eurasia and vice versa. Although no characteristics indicative of mammalian adaptation was found in the Taiwanese isolates, temporal changes in the haemagglutinin cleavage site sequences were observed. This study provides a comprehensive overview of the evolutionary dynamics of H10 avian influenza viruses isolated from wild birds in Taiwan, emphasizing the complexity of intercontinental gene flow and viral reassortment. Currently, no consistent molecular markers indicating the impact of H10 avian influenza viruses on mammals or poultry have been identified. Notably, the observed changes in the haemagglutinin cleavage site sequences among Eurasian viruses suggest potential antigenic variations, indicating a need for further investigation into these changes. This potential highlights the necessity of ongoing surveillance to track the evolution and transmission dynamics of these viruses.