Studies On Embryo Vaccination Of A Recombinant Newcastle Disease Virus Expressing VP2 Gene Of Infectious Bursal Disease Virus

Chicken embryo immunization can generate immune response sooner than conventional approach, lead low stress response and reduce vaccine pollution, inject accurate and consistent, decrease labor costs.This method has been the research focus of scholars in the worldwide.A recombinant Newcastle disease virus(rL-VP2) expressing the VP2 gene of vvIBDV Gx strain was used in the study.After determining the EID₅₀, MDT, ICPI and IVPI of rL-VP2, the vaccine was proved that kept the low pathogenicity similar with LaSota vaccine strain and replicated with high-titer similar to that of parental NDV strain LaSota in chicken embryos.The vaccine was administered through amnion cavity to 18-day-old specific-pathogen-free embryos with different doses. The percentage hatchability of each group was counted. To evaluate the efficacy of the recombinant vaccine against NDV and IBDV, the antibody titers were detected at 9th day, 14th day and 21st day post hatching. The results showed that the hatchability or 3rd week survivability did not decrease and the hatched chicks could obtain specific active immunity with higher antibody levels than other groups when the dose of 104 EID₅₀/egg was administered. According to the results, the optimum dose of rL-VP2 using in ovo was 104 EID₅₀/egg.The group which administered with the dose of 104 EID₅₀/egg was challenged with a highly virulent NDV strain F48E9 and vvIBDV Gx strain at four weeks post-hatched. The result showed that 100% of chickens was protected from challenge, the weight of the chickens did not have significant difference(P>0.05) from the control group, and bursa of Fabricius did not present significant damage in this group.These results are promising for the development of embryo safe efficacious IBDV and NDV vaccines for in ovo application.