Characterization of the novel H6N1 avian influenza viruses in a broiler duck farm in Korea from 2023 to 2024.

Low-pathogenicity avian influenza (LPAI) viruses of the H6Nx subtypes are widely detected in wild birds and occasionally infect poultry. During the avian influenza virus (AIV) surveillance programme in South Korea in 2023-2024 winter season, H6N1 AIVs were detected in wild birds and a broiler duck farm and the farm experienced recurrent H6N1 AIV infection. To characterise the genetic features and potential epidemiological relationships between these H6N1 AIVs, we analysed samples subjected to whole-genome sequencing (WGS), and representative isolates were selected for phylogenetic and genotype constellation analyses. We identified 18 H6N1 isolates, comprising 14 from wild birds and four from the affected farm. These isolates were classified into eight genotypes (G1-G8); notably, G1 was the most prevalent in wild birds, and all farm isolates belonged to G1. Our results strongly suggest that wild birds likely contributed to the initial introduction of G1 H6N1 AIV into the farm, and that the subsequent occurrence on the farm indicates viral persistence in the farm environment. These findings underscore that strengthened biosecurity, including thorough cleaning and disinfection of farm facilities, is required to reduce the risk of recurrent circulation of LPAI viruses in poultry production systems.