No abstract

The roles of Fusion gene in the virulence of Newcastle disease virus has been well established but the extent of its variation among the newly identified XIV, XVII and XVIII genotypes which are predominantly found in Central and West Africa have until recently been understudied and LaSota vaccine strain protection against mortality and morbidity against XIV genotype is the least reported. In this study, F gene of vNDV isolated from samples collected in Nigeria from chicken cadaver from vaccinated chicken flocks showing high mortality, clinical signs and post-mortem lesions attributable to ND during March and April, 2020 were sequenced and analysed for information about genetic changes. Results showed that all isolates from our study have virulent cleavage site sequence 112-RRRKR-116/F117 and clustered within genotype XIVb. Sequence analysis show K78R mutation in the A2 antigenic epitope in all isolates, and more along the F gene which vary in some instances within the isolates. Mutation in this A2 antigenic epitope has been reported to induce escape mutation to monoclonal antibodies generated using NDV LaSota strain. Averages of antigenic variability and percentage homology between the isolates and commonly used vaccines is 0.24; 81.40% and 0.22; 81.90% for LaSota and Komorov vaccines respectively. Nucleotide sequences was assigned accession numbers OK491971-OK491977. Many substitutions were observed in the isolates and some of their functions are yet to be determined.

The roles of fusion gene in the virulence of Newcastle disease virus are well established, but the extent of its variation among the XIV, XVII, and XVIII genotypes reported in Central Africa and West Africa has until recently been understudied. In this study, virulent Newcastle disease virus (vNDV) was isolated from dead chickens among vaccinated flocks between March and April 2020. Fusion (F) gene was sequenced and analysed for characterization and information about genetic changes. Many substitutions were observed along the region and some of their functions are yet to be determined. Results showed that all study isolates have virulent cleavage site sequence 112-RRRKR-116/F117 and clustered within genotype XIVb. Sequence analysis showed K78R mutation in the A2 antigenic epitope in all isolates and more along the F-gene which varied in some instances within the isolates. Mutation in this A2 antigenic epitope has been reported to induce escape mutation to monoclonal antibodies generated using the NDV LaSota strain. The range of percentage nucleotide and amino acid homology between the study isolates and commercially available vaccine strains is 81.14%–84.39% and 0.175–0.211, respectively. This report provides evidence of vNDV among vaccinated chicken flock and molecular information about circulating vNDV strains in Kano State, Nigeria, which is useful for the development of virus matched vaccines. Newcastle disease (ND) surveillance and molecular analysis of circulating strains in this region should be encouraged and reported. Furthermore, ND outbreaks or cases among vaccinated poultry presented to veterinary clinics should be reported to the state epidemiologist. Nucleotide sequences were assigned accession numbers OK491971–OK491977.