Biological and Molecular Characterization of Circulating Newcastle Disease Virus in Chickens of Trishal, Mymensingh, Bangladesh

Velogenic Newcastle disease virus (VNDV) causes a highly contagious disease in poultry, with mortality rates reaching 100% in susceptible populations during severe outbreaks. The study aimed to evaluate the biological and molecular characteristics of circulating NDVs in chickens in Trishal, Mymensingh, Bangladesh, from May 2023 to February 2024. A total of 35 samples suspected of ND (lung, trachea, and caecal tonsils) were collected, processed, prepared as inocula, and inoculated into 10–12-day-old ECEs through the allantoic cavity. Following 24 hours of inoculation, 27 (77%) isolates from ECEs were initially identified as NDV by reverse transcription polymerase chain reaction (RT-PCR) using matrix (M) and fusion (F) gene-specific primers and confirmed by partial sequencing of the M and F genes. The pathogenicity of the isolated NDVs was evaluated using the mean death time (MDT), intracerebral pathogenicity index (ICPI), intravenous pathogenicity index (IVPI), and cytopathic effects (CPEs) in chicken embryo fibroblast (CEF) cells. MDT <60 hours, ICPI >1.5, IVPI >1.7, and CPEs (cellular granularity, cell rounding, cytoplasmic vacuolation, and syncytia formation) indicated that the isolates had a velogenic pathotype. Further, the pathotype and genotype were confirmed by sequencing of the F gene and phylogenetic analysis. The F-gene cleavage motif “RRQKRF” at amino acid positions 112–117 indicated that the isolate was velogenic, whereas the phylogenetic tree and BLAST analysis showed 100% identity with the velogenic sub-genotype XIII.2.3 of genotype XIII NDVs.The study demonstrated the circulation of velogenic G-XIII.2.3 NDVs among the poultry population in Trishal Upazila, Mymensingh District, Bangladesh, resulting in chicken mortality.