Expression of duck hepatitis A virus type 1 VP3 protein mediated by avian adeno-associated virus and its immunogenicity in ducklings.

The avian adeno-associated virus (AAAV) is a replication-defective nonpathogenic virus that has been proved to be useful as a viral vector in gene delivery. In this study, the feasibility of AAAV for transgenic expression of duck hepatitis A virus (DHAV) VP3 structural protein and its ability to induce protective immunity in ducklings was assessed. The recombinant AAAV (rAAAV-VP3) expressing the VP3 protein was prepared by co-infection of Sf9 cells with recombinant baculovirus (rBac-VP3) containing VP3 gene flanked by inverted terminal repeats (ITRs) of AAAV and the other two recombinant baculovirus expressing AAAV functional and structural genes, respectively. The generation of rAAAV-VP3 was demonstrated by electron microscopy, immunofluorescence assay, and western blot analysis. One day old ducklings were inoculated with rAAAV-VP3 or commercial attenuated vaccine and then challenged with DHAV-1 strain SH two weeks post vaccination. Anti-DHAV-1 antibodies were detected in all vaccinated groups by ELISA, and the titers between the rAAAV-VP3 group and the attenuated vaccine group were not statistically significant. Real time RT-PCR analysis showed that the virus copy numbers in the livers of the PBS control group were significantly higher than that of the rAAAV-VP3 and attenuated vaccine groups. In conclusion, we demonstrated that the VP3 expression mediated by rAAAV in ducklings could induce protective immunity against DHAV challenge, and this could be a candidate vaccine for the control of duck viral hepatitis. Keywords: avian adeno-associated virus; duck hepatitis A virus; VP3 gene; immunogenicity.