Newcastle disease (ND) is prevalent worldwide and causes significant clinical and economic losses to the poultry industry. Current vaccine programs using live attenuated vaccines and inactivated vaccines have limitations, and new vaccines with distinct features are needed. To offer an alternative solution to control ND, a turkey herpesvirus vector Newcastle disease vaccine (HVT/ND) expressing the fusion gene of Newcastle disease virus (NDV) has been developed. First, immunogenicity of the HVT/ND was evaluated in specific-pathogen-free layer chickens after vaccination by the in ovo route to 18-day-old embryos or by the subcutaneous route to 1-day-old chicks. Antibodies against NDV were detected at 24 days of age using a commercial NDV enzyme-linked immunosorbent assay (ELISA) kit and the hemagglutination inhibition test. At least 90% of chickens were protected against challenge with velogenic neurotropic NDV Texas GB strain (genotype II; pathotype velogenic) at 4 wk of age, while none of the nonvaccinated, challenged controls were protected from challenge. Second, the age at which a vaccinated chicken elicits an immunologic response to the HVT/ND prepared for this study, and thus is protected from ND virus, was assessed in commercial broiler chickens after in ovo vaccination of 18-day-old embryos. Challenge was conducted using a low-virulence NDV strain (genotype II; pathotype lentogenic) via the respiratory tract each week between 1 and 5 wk of age, in order to mimic the situation in areas where virulent NDV strains do not normally exist and low-virulence strains cause mild respiratory symptoms leading to economic losses. Protection was evaluated by the presence or absence of isolated virus from tracheal swabs at 5 days postchallenge. Partial protection was observed at 3 wk of age, when 6 out of 10 (60%) chickens were protected. Full protection was obtained at 4 and 5 wk of age, when 9 out of 10 (90%) and 10 out of 10 (100%) chickens were protected, respectively. Finally, protection against challenge with virulent Texas GB strain at 19 wk of age was evaluated in commercial female layer chickens vaccinated at 1 day of age with HVT/ND. All of the vaccinated chickens were protected, while all of the challenge controls succumbed to the challenge. Furthermore, anti-NDV antibodies measured by ELISA were maintained through 50 wk of age.
Protección y respuesta de anticuerpos por una vacuna contra la enfermedad de Newcastle con un herpesvirus de los pavos como vector.
La enfermedad de Newcastle (ND) es prevalente en todo el mundo y causa pérdidas clínicas y económicas significativas para la industria avícola. Los programas de vacunación actuales con vacunas vivas atenuadas y vacunas inactivadas tienen limitaciones, y se necesitan nuevas vacunas con características diferentes. Para ofrecer una solución alternativa para controlar a la enfermedad de Newcastle, se desarrolló una vacuna contra la enfermedad de Newcastle utilizando a un herpesvirus de pavo como vector (HVT/ND) que expresa el gene de fusión del virus de la enfermedad de Newcastle (NDV). En primer lugar, se evaluó la inmunogenicidad de la vacuna HVT/ND en aves de postura libres de patógenos específicos después de la vacunación in ovo a los 18 días de desarrollo embrionario, o por vía subcutánea en pollos de un día de edad. Se detectaron anticuerpos contra la enfermedad de Newcastle a los 24 días de edad con un estuche comercial del ensayo de inmunoabsorción con enzimas ligadas (ELISA) para Newcastle y por la prueba de inhibición de la hemaglutinación. Al menos el 90% de los pollos estuvieron protegidos contra el desafío con la cepa velogénica neurotrópica GB Texas (genotipo II; patotipo velogénico) a las cuatro semanas de edad, mientras que ninguna de las aves control no vacunadas, estuvo protegida ante el desafío. En segundo lugar, se evaluó la edad a la que los pollos vacunados desarrollaban u
