Genetic characterization of hepadnaviruses associated with histopathological changes in the liver of duck and goose embryos

Avian hepadnaviruses are etiological agents of hepatitis B, that has been identified primarily in ducks, and more recently in various avian species. In this paper, 16 hepadnaviruses were detected by polymerase chain reaction (PCR) in the field samples from dead embryos of commercially reared domestic duck and goose. Based on the molecular analysis of the S-protein gene sequences and phylogenetic Neighbor-joining tree, identified viruses were clustered in the same genetic group, indicating no host-related diversity. Both duck and goose-origin hepadnaviruses were grouped within the cluster consisting of “Western-country” and “Chinese” duck hepatitis B (DHBV) isolates, showing more evolutionary distances with other known avian hepadnaviruses. Histopathologically, the lesions observed in the liver tissue from hepadnavirus positive duck and goose embryos varied from low to mild degree of perivascular mononuclear cells and mixed cell infiltrations, followed by mild vacuolar changes. Small focal necrotic changes in the liver parenchyma, and bile ductular proliferation were also found in examined liver samples. Generally, the microscopic findings resemble those described in experimentally infected ducks, while this was the first description of hepadnavirus associated lesions in domestic goose. Although hepadnaviruses are considered to have a very narrow host range, this study showed that domestic ducks and geese are susceptible to infection with genetically almost identical hepadnaviruses, that were likely to produce similar microscopic changes in the liver of both duck and goose embryos. The impact of naturally occurred hepadnavirus infection and possible synergistic interactions with other infectious or non-infectious agents on embryo viability needs further investigation.