A Newcastle disease live virus vaccine is safe and efficacious at various storage conditions

Pure, potent and efficacious vaccines could help in the control of Newcastle disease (ND). The present study was designed to evaluate the thermo-stability of a live-attenuated ND virus vaccine containing the Mukteswar strain and to genetically characterize the seed virus. Moreover, the presence of extraneous agents (Fowl adenovirus, Mycoplasma, Salmonella Pullorum, and Salmonella Gallinarum) was assessed using polymerase chain reactions (PCR) optimized for detection in a panel. The vaccine was evaluated for its potency and efficacy after storage at 4°C, 25°C and 37°C for 36, 48, 96 and 144 hours. A total of 100 commercial broiler chickens were randomly divided into six groups and immunized with the vaccine stored at specified temperatures for the given times. Blood samples were collected on days 0, 7, 14, 21 and 28 post-vaccination, sera were separated and antibody titers were assessed using hemagglutination inhibition (HI) assay. The data were analyzed by two-way analysis of variance (ANOVA) and multivariate analysis of variance (MANOVA). Reverse-transcription  PCR targeting the F gene of Newcastle disease virus (NDV) and subsequent sequence analysis confirmed the presence of NDV in the vaccine seed (deposited to GenBank Acc. Nos. MK310260 and MK310261). Phylogenetic analysis revealed a close resemblance of the vaccine virus with other Avian Avulaviruses (NDV class II Genotype III viruses and more specifically with NDV Mukteswar vaccine strains), yet it was distinct from NDV class II Pakistani field isolates, which grouped into genotype XIII.2.1. The PCR testing confirmed that the vaccine was free from extraneous agents. The present study's findings propose an alternative rapid PCR-based method to evaluate the purity of NDV live vaccines. Together these data suggest that the tested vaccine is pure, potent and efficacious, yet continuous maintenance of the cold chain for vaccine storage is recommended to maintain its potency and efficacy.