Epidemiological and recombination analysis of duck hepatitis B virus in domestic ducks from Hunan province, China.

Duck hepatitis B virus (DHBV), a member of the Avihepadnavirus genus, serves as an important model for human hepatitis B virus (HBV) due to shared genomic and replication features. Although typically asymptomatic in adult ducks, DHBV infection is associated with substantial economic losses in commercial flocks, including reduced egg hatchability and impaired duckling development. As the world's largest producer of waterfowl, China faces significant economic threats from such endemic viruses, highlighting the importance of understanding DHBV epidemiology in local populations. In this study, we conducted an epidemiological investigation of DHBV in central China by analyzing 101 liver samples from domesticated ducks in Hunan province. A high infection prevalence of 46.5% (47/101; 95% CI: 37.1-56.2%) was detected by nested PCR. Genetic characterization based on 25 complete genomes revealed that all local strains clustered within the DHBV-I and DHBV-II genotypes, with no evidence of the Western-associated DHBV-III. Phylogenetic analysis suggested cross-species transmission between ducks and geese and indicated inter-provincial circulation of viral lineages. Importantly, we identified four statistically supported recombination events among the co-circulating strains, demonstrating active sympatric recombination as a key driver of viral diversity. These findings confirm the endemic circulation and ongoing evolution of DHBV in Chinese duck populations, underscoring the need for sustained genomic surveillance to monitor the emergence of novel variants.