Geographic distribution and genetic diversity of Newcastle disease virus in pigeons from Pakistan

Newcastle disease virus (NDV) is among the most important viruses of poultry; however, variants also cause clinical diseases in birds of the family Columbidae. From 2014 onwards, notable mortality rates have been observed in racing and rock pigeons, with a correlation to subgenotypes XXI.1.1 and XXI.1.2 of genotype XXI in Pakistan. In this study, we performed isolation and genetic characterization of 29 pigeon-derived NDV isolates of sub-genotypes XXI.1.1, XXI.1.2 and VII.2. Phylogenetic analysis based on complete fusion gene sequences classified seven (n = 7) isolates into sub-genotype XXI.1.1 and they were genetically closely related to isolates previously characterized in Pakistan (0.05-0.43% nucleotide divergence), and in Iran, Russia, Egypt, Nigeria, Kazakhstan and Ukraine (3.75% to 6.67% nucleotide divergence) in the period from 2005-2018. In addition, nineteen (n = 19) isolates were clustered with viruses previously isolated in Pakistan (2014-2018) in sub-genotype XXI.1.2. In addition, three (n = 3) F-gene sequences assigned to subgenotype VII.2 were identified along with viruses repeatedly isolated (2011-2020) from several poultry and non-poultry avian species in Pakistan. The analysis showed that all isolates of sub-genotypes XXI.1.1 and XXI.1.2 were mesogenic (1.42-1.49) and the isolates belonging to sub-genotype VII.2 were velogenic (1.63-1.71) in nature according to the intracerebral pathogenicity index (ICPI). This study delivers a comprehensive description of the prevalence of sub-genotypes XXI.1.1 and XXI.1.2 in Pakistan since 2014. Additionally, it underscores the role of free-range pigeons as effective carriers of virulent sub-genotype VII.2 viruses, impacting both poultry and non-poultry avian species reared in open environments.RESEARCH HIGHLIGHTSVirulent NDV genotypes were repeatedly isolated from pigeons.Evidence of epidemiological links among viruses isolated from various locations.Distinct phylogenetic branches suggest separate, simultaneous evolution of NDVs.Study information could be helpful in the development of an effective vaccine.