Occurrence and Molecular Characterization of Newcastle Disease Virus Strains in Chicken Flocks in Ibadan, Nigeria: Implications for Vaccine Strain Compatibility

Newcastle Disease (ND) poses a significant threat to poultry health and economic stability in Nigeria, with outbreaks affecting both smallholder and commercial farms. Despite vaccination efforts, the persistence of ND outbreaks is attributed to the genetic diversity of circulating Newcastle disease virus strains, which often differ from vaccine strains. This study investigated the occurrence and molecular characteristics of ND virus in chicken flocks within Ibadan between June and September 2024. A cross-sectional study was conducted by collecting samples from chickens that were tentatively diagnosed as ND at Poultry Diagnostic Centers in Ibadan. The presence of ND virus was confirmed through haemagglutination and haemagglutination inhibition tests, followed by molecular analysis using reverse transcription-polymerase chain reaction (RT-PCR) targeting the F-gene. Genetic sequencing and phylogenetic analysis assessed the relationship between detected strains and available vaccine strains. Out of 297 poultry cases submitted for diagnostic evaluation, 26 were suspected to be ND based on clinical signs and pathological findings, yielding an occurrence rate of 8.8%. Following haemagglutination and haemagglutination inhibition tests using ND-specific antiserum, 12 samples (4.04%) tested positive for ND virus. At the same time, PCR analysis confirmed the presence of the ND virus in 11 out of the 12 cases, with strains showing high genetic similarity to local field strains but notable variations from existing vaccine strains. The analysis indicated that the strains belonged to the avian paramyxovirus 1 lineage, with a sequence identity of 99.63% among them. The study highlights the need for ongoing molecular surveillance of ND virus in Nigeria to guide vaccination strategies considering the genetic diversity of circulating strains.