Genetic characterization of LPAI-H4N2 and H4N8 viruses recovered from free-grazing ducks in Thailand

nfluenza A viruses (IAVs) can infect birds and various mammals. In this study, we retrospectively isolated and characterized IAVs (n=8) from oropharyngeal and cloacal swab samples of free-grazing ducks collected during December 2018 to December 2021, by using egg inoculation and whole-genome sequencing. The IAVs could be subtyped as IAV-H4N2 (n = 3) and IAV-H4N8 (n = 5) using real-time RT-PCR assays. Genetic and phylogenetic analyses revealed that all eight genes of Thai IAV-H4 belong to the Avian Eurasian lineage. Both Thai IAV-H4N2 and IAV-H4N8 exhibited low pathogenic avian influenza (LPAI) characteristics and were susceptible to oseltamivir and amantadine. This study did not detect any reassortant viruses among IAV-H4N2 and IAV-H4N8. Overall, our findings suggest that IAV-H4N2 and IAV-H4N8 are endemic and circulating among free-grazing ducks in Thailand. Therefore, routine surveillance of IAVs in free-grazing ducks is necessary to monitor the emergence of new reassortant and potential virulent viruses.