Genome analysis and recombination characterization of duck hepatitis B virus isolated from ducks and geese in central China, 2017 to 2019.

Owing to its high similarity to human hepatitis B virus (HBV), duck HBV (DHBV) is often used as an essential model for HBV research. Although intergenotypic recombination of HBV is common, it remains unclear whether the intergenotypic recombination of human HBV is exactly the same as that of DHBV. In this study, 119 serum samples of duck and goose were collected from 51 farms (29 duck and 22 goose farms) in the central and eastern regions of China. A total of 22 strains isolated from the 22 DHBV positive flock were sequenced. Genome sequence alignment revealed that the duck- and goose-origin strains shared the highest and lowest similarities (99.7 and 90.52%, respectively). The complete genomes of these DHBV and 31 reference strains were analyzed using phylogenetic methods and classified into 3 clusters, which corresponded to the previously identified DHBV-I, DHBV-II, and DHBV-III branches. Recombination analyses of the 53 DHBV genomes indicated 2 major intergenotypic recombination events with high confidence values. These recombination events occurred between the genotypes of the Chinese isolates Y180813HB (Chinese branch [DHBV-Ⅰ]) and E170101AH (Chinese branch [DHBV-Ⅱ]) and the Western isolate DHBV-XY (Western branch [DHBV-Ⅲ]), resulting in the emergence of 2 Chinese recombinant isolates Y190303HN and Y170101HB. In addition, 40% (2/5) goose-origin and 58.8% (10/17) duck-origin DHBV in this study harbored the mutation site of G133E in preS, which promote the pathogenicity of DHBV. This is the first study to report on the genome analysis and recombination characterization of DHBV isolated from Chinese geese. Further, continuous investigation and molecular identification of DHBV should be conducted to attract researchers' attention.