Efficacy of Two Commercial Newcastle Disease Virus Lentogenic Vaccines Against Virulent Asiatic-Type Newcastle Disease Viruses

Abstract

Seventy-five unvaccinated chickens were divided into three equal groups. Chickens in group A received RDVF [Lentogenic strain of Newcastle disease virus (NDV)] vaccine oculonasally at 7 d of age and through drinking water at 4 wk of age. Chickens in group B were vaccinated with LaSota (Lentogenic strain of NDV) in the same way. Group C birds were kept as unvaccinated challenge controls. Five birds from each of these groups were moved to separate pens at 7 wk of age and were challenged with a field isolate No. 105 of virulent NDV (C1, based on monoclonal antibody grouping or Asiatic type, which was isolated from a disease outbreak). Similarly, five birds from each of the groups were moved to different pens at same age and challenged with the reference strain of the virulent NDV. All the unvaccinated birds died postchallenge, but both vaccinated groups withstood the challenge. Serum samples were collected from all three groups at different times, and antibody levels (against NDV) were measured by hemagglutination inhibition test, passive hemagglutination test, and enzyme-linked immunosorbent assay. The possibility of Asiatic-type NDV causing outbreaks in commercially vaccinated flocks is discussed in this paper.