Molecular and Pathological Evaluation of a Velogenic Newcastle Disease Virus Strain Circulating in Vietnam

The Newcastle disease virus (NDV) poses a major challenge to poultry farming in Vietnam as it continues to threaten both economic and food security. Despite vaccination efforts, outbreaks caused by velogenic NDV strains continue to occur, indicating gaps in our understanding of the pathogenicity of these viruses. In this study, a velogenic NDV strain (genotype VII.2) was isolated from vaccinated chickens during an outbreak in southern Vietnam. Whole genome sequencing and phylogenetic analyses confirmed that this isolate belongs to a genotype associated with virulent NDV strains. The strain had an intracerebral pathogenicity index (ICPI) of 1.81 and a mean-death-time (MDT) of 56 hours. Experimental infection of domestic chickens showed a rapid onset of severe clinical signs, extensive tissue damage, and a high mortality rate, even in co-housed, uninfected chickens. Virus excretion via the oral cavity and cloaca of the experimental chickens facilitated rapid transmission within the flock. These results underscore the urgent need for enhanced epidemiological surveillance and tailored vaccination strategies to mitigate the impact of NDV outbreaks in Vietnam. This study provides important insights into the pathogenicity, transmission, and lesion profile of NDV genotype VII.2, contributing to the development of effective control measures.