Genetic characterization of Duck Hepatitis A Viruses isolated in China

In recent years, the spread of Duck Hepatitis A Viruses (DHAVs) has represented a serious threat and significant economic impact in duck industry of China. The sixteen reported DHAV isolates (15 DHAV-1 strains and one DHAV-3) were identified from infected ducks with clinical symptoms in China between 2009 and 2012. In the present study, the virulence of these viruses and complete sequences of the virion protein 1 (VP1) genes of the 16 DHAVs were characterized. The median embryonic lethal doses (ELD50) of the second generation duck embryo allantoic fluid of the 16 DHAV isolates were calculated on duck and chicken embryos. The results demonstrated that the various DHAV-1 strains have shown different pathogenic ability in embryos, and duck eggs were more susceptible to DHAV than chicken eggs. The histopathological examination revealed significant signs of virus infection, severe vacuolation, and hepatocyte necrosis. Phylogenetic analyses indicated that the 15 DHAV-1 viruses display significant correlation in their geographic distribution. The DHAV-1 strains isolated from Shandong Province were more evolutionarily divergent than the JX strains. There were two hypervariable regions in the VP1 protein, which may determine the virulence of DHAV-1 isolates in chicken eggs but not virulence in duck eggs. These results demonstrate the genetic and biological diversity of DHAVs in China and aid in understanding the epidemiology and evolution of DHAVs.