Circulation and recombination-driven diversity of duck hepatitis B virus in domesticated geese in Guangdong, southern China.

Duck hepatitis B virus (DHBV) is a valuable comparative model for human hepatitis B virus (HBV) due to its shared genomic organization and reverse transcription-based replication, despite having only ∼40% nucleotide identity. Infection is generally asymptomatic in adult birds but causes reduced hatchability, impaired embryo development, and growth retardation in young waterfowl, leading to economic losses. As a major waterfowl producer, China faces risks from this endemic virus. This study analyzed 901 deceased domesticated geese liver samples from five regions in Guangdong province, southern China. Nested PCR screening revealed an overall infection prevalence of 34.1% (307/901). Amino acid analysis of the preS domain of the large envelope protein showed extensive variability, including the G133E mutation in 47.7% (21/44) of strains and genotype-associated substitutions at residues 117 and 120. Genetic characterization of 44 complete genomes revealed exclusive circulation of genotypes I and II (DHBV-I and DHBV-II), with no detection of the Western-associated DHBV-III. Phylogenetic analysis indicated frequent duck-goose host-switching and viral circulation between provinces, likely facilitated by the live-poultry trade. We identified 20 recombination events, six of which involved our sequences as parental strains, demonstrating that active recombination among co-circulating strains drives viral heterogeneity in Guangdong. These findings highlight the ongoing circulation and evolutionary complexity of DHBV in southern China and underscore the need for longitudinal genomic surveillance to detect emerging variants.