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Abstract
Newcastle disease (ND) is one of the most economically important poultry diseases. Despite intensive efforts with current vaccination programs, this disease still occurs worldwide, causing significant mortality even in vaccinated flocks. This has been partially attributed to a gap in immunity during the post-hatch period due to the presence of maternal antibodies that negatively impact the replication of the commonly used live vaccines. In ovo vaccines have multiple advantages and present an opportunity to address this problem. Currently employed in ovo ND vaccines are recombinant herpesvirus of turkeys (HVT)-vectored vaccines expressing Newcastle disease virus (NDV) antigens. Although proven efficient, these vaccines have some limitations, such as delayed immunogenicity and the inability to administer a second HVT vaccine post-hatch. The use of live ND vaccines for in ovo vaccination is currently not applicable, as these are associated with high embryo mortality. In this study, recombinant NDV-vectored experimental vaccines containing an antisense sequence of avian interleukin 4 (IL4R) and their backbones were administered in ovo at different doses in 18-day-old commercial eggs possessing high maternal antibodies titers. The hatched birds were challenged with virulent NDV at 2 weeks-of-age. Post-hatch vaccine shedding, post-challenge survival, challenge virus shedding, and humoral immune responses were evaluated at multiple timepoints. Recombinant NDV (rNDV) vaccinated birds had significantly reduced post-hatch mortality compared with the wild-type LaSota vaccine. All rNDV vaccines were able to penetrate maternal immunity and induce a strong early humoral immune response. Further, the rNDV vaccines provided protection from clinical disease and significantly decreased virus shedding after early virulent NDV challenge at two weeks post-hatch. The post-challenge hemagglutination-inhibition antibody titers in the vaccinated groups remained comparable with the pre-challenge titers, suggesting the capacity of the studied vaccines to prevent efficient replication of the challenge virus. Post-hatch survival after vaccination with the rNDV-IL4R vaccines was dose-dependent, with an increase in survival as the dose decreased. This improved survival and the dose-dependency data suggest that novel attenuated in ovo rNDV-based vaccines that are able to penetrate maternal immunity to elicit a strong immune response as early as 14 days post-hatch, resulting in high or full protection from virulent challenge, show promise as a contributor to the control of Newcastle disease.
Highlights
Newcastle disease (ND), a devastating poultry disease that can reach 100% mortality in naïve birds, is caused by virulent strains of Newcastle disease virus (NDV) [1]
Previous studies with chickens of different ages have demonstrated that chickens vaccinated with strains that were antigenically matched to the challenge virus shed significantly less amount of the challenge virulent NDV (vNDV) than the amount excreted by chickens vaccinated with heterologous vaccines [15,16,17]
There were no significant differences in survival between the experimental ZJ1*L, ZJ1*L-IL4R, and LS-IL4R vaccine groups and the Hatch, brain heart infusion (BHI), and recombinant HVT (rHVT)-ND control groups, but the percentage survival in these control groups was numerically higher, with a negative correlation between vaccine dose and post-hatch survival observed
Summary
Newcastle disease (ND), a devastating poultry disease that can reach 100% mortality in naïve birds, is caused by virulent strains of Newcastle disease virus (NDV) [1]. This virus species, recently renamed Avian orthoavulavirus 1, is a member of the family Paramyxoviridae [2,3]. Several avian vaccines, engineered to co-express immunostimulatory cytokines, have been suggested to improve protective immunity [12]. Another approach that has been explored is the use of antigenically matched vaccines. Passively transferred maternal anti-NDV antibodies, protecting chickens during the crucial early weeks of life, interfere with development of host immunity following vaccination [18]
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