Detection and Molecular Characterisation of Genotype Vii Newcastle Disease Virus Isolates From Commercial Chickens in Peninsular Malaysia

Newcastle disease (ND) caused by Newcastle disease virus (NDV) is a significant threat to the global poultry industry, with recurring outbreaks of varying virulence. In Malaysia, NDV has been circulating since its first detection in 1934, with genotype VII being the predominant strain in recent years. This study aimed to characterise NDV isolates from commercial poultry in Peninsular Malaysia between 2021 and 2022, during the COVID-19 pandemic. Nineteen suspected ND cases from various states were investigated through virus isolation, RT-PCR, molecular characterisation, and pathotyping. The F gene was sequenced, revealing that all isolates contained virulent polybasic amino acid motifs at the fusion protein cleavage site. Phylogenetic analysis showed that the isolates belonged to genotype VII, with sub-genotypes VII.2/VIIh, VII.2/VIIi, and VII.1.1 identified. A selected isolate, UPM/NDV/IBS008/2021, exhibited virulence with an intracerebral pathogenicity index (ICPI) of 1.75 and a mean death time (MDT) of 88 hours, classifying it as a velogenic strain. This study underscores the persistent threat of genotype VII NDV, despite vaccination efforts, and highlights the need for continued surveillance and control measures in Malaysia and surrounding regions