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Abstract
In ovo vaccination has been used commercially for over 20 years to control avian diseases due to its significant advantages over conventional vaccination. The advantages of in ovo vaccination include a significant reduction in costs, induction of earlier immunity, uniform vaccine delivery, and reduction of stress. In ovo vaccination programs currently available for Newcaste disease virus (NDV) have limitations, including interference by maternal antibodies (MatAbs) and the inability to induce protective immunity until four weeks post vaccination. Current biosecurity measures and vaccination protocols have been unable to stop the occurrence of outbreaks with virulent vNDV around the world particularly in developing countries. Thus, it is imperative to develop new effective vaccines able to overcome the maternal antibody inhibition and confer the earliest protection against vNDV. The poultry industry needs vaccines able to boost both cellular and humoral immune response and to achieve clearance of the challenge virus without compromising the flocks health. In a first set of experiments, attenuated recombinant NDV vaccines containing either an antisense chicken IL-4 insert (ZJ1-L-IL4R), IL-2 expressing variant (-IL2), IL-10 expressing variant (-IL-10) or IFN expressing variant (-IFN) were tested as vaccine candidates against homologous challenge with a genotype VIId NDV. Results show that strain ZJ1-L-IL4R may serve as a viable vaccine candidate for in ovo vaccination against NDV, as it compared favorably to the commercial strains regarding protection to challenge, yet displayed lower mortality rates compared with the in ovo live vaccine candidates for NDV. In another set of experiments, we evaluated the modulatory effects of an attenuated recombinant Newcastle disease virus vaccine containing an antisense chicken interleukin 4 insert (IL4R) on the chicken adaptive immune response. Our results did not confirm that the improvement in survival and body weight seen in birds vaccinated with ZJ1-L-IL4R compared to ZJ1-L is due actions by the antisense RNA.