Molecular Characterization of Newcastle Disease Virus Strains Circulating in Backyard Poultry Flocks in Nasarawa State

Newcastle disease (ND) is a highly contagious and economically devastating viral disease affecting poultry globally, with virulent strains causing near-total flock losses in unvaccinated backyard chickens. Backyard poultry production is a primary livelihood strategy for rural households in Nasarawa State, North Central Nigeria, yet ND surveillance data from this area are limited. This study molecularly characterized Newcastle disease virus (NDV) strains circulating in backyard poultry flocks across five local government areas in Nasarawa State. Cloacal and tracheal swabs were collected from 160 chickens exhibiting respiratory and neurological signs. RNA was extracted and RT-PCR performed targeting the NDV fusion (F) gene. Positive samples were sequenced to determine pathogenicity indices based on deduced cleavage site motifs. NDV was confirmed in 36.9% of symptomatic birds. Cleavage site analysis classified 78% of positive isolates as velogenic, possessing the polybasic amino acid motif associated with virulent strains. Phylogenetic analysis clustered circulating strains within Genotype XVII, a lineage previously associated with outbreaks in sub-Saharan Africa. These findings confirm velogenic NDV circulation in Nasarawa backyard flocks and indicate the failure of current vaccination coverage to prevent virulent strain introduction. Keywords: Newcastle disease virus, fusion gene, velogenic, backyard poultry, Nasarawa State.