Molecular characterization of virulent genotype XIII Newcastle disease virus isolates from desi-chickens in Namakkal, South India.

Newcastle disease (ND), one of the most devastating viral infections of poultry, remains a major threat to global poultry production. The main focus of the study was to isolate and characterize the Newcastle disease virus (NDV) circulating among desi-chickens of Namakkal district of Tamil Nadu. Tissue samples were collected from 20 flocks of desi-chickens in and around Namakkal district suspected of NDV outbreaks. Out of 20, all flocks were found to be positive for NDV by RT-PCR amplification of a 535 bp fragment of the F gene. The samples were inoculated into 9–11 days old embryonated chicken eggs via allantoic cavity route and mortality with occipital haemorrhage was observed after 30 h of infection. Histopathological examination of NDV infected embryos revealed severe congestion, mild to extensive hemorrhage and degeneration of white matter in the brain. Further, the samples were also inoculated into chicken embryo fibroblast cell cultures which revealed cytopathic effects viz., cell rounding, cell death and detachment of monolayer after 24 h of infection. Sequence analysis of F gene revealed R-R-Q-K-R-F at 112-117th position of fusion protein cleavage site. Further, the sequences in this study were identical to that of genotype XIII of NDV based on sequencing as well as phylogenetic analysis. It was concluded that velogenic genotype XIII NDV was identified as the cause of recent outbreaks in desi-chickens in the sampled region.