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<em><sup>a</sup>The Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences (SLU), Ulls v&auml;g 2B, SE-751 89 Uppsala, Sweden<br />
<sup>b</sup>Department of Virology, Immunobiology and Parasitology, National Veterinary Institute (SVA), Ulls v&auml;g 2B, SE-751 89 Uppsala, Sweden<br />
<sup>c</sup>Quality Control Laboratory, Veterinary Research Institute, Lahore, Pakistan<br />
<sup>d</sup>Disease Section, Poultry Research Institute, Rawalpindi, Pakistan<br />
<sup>e</sup>University Diagnostic Laboratory, University of Veterinary and Animal Science, Lahore, Pakistan<br />
<sup>f</sup>Department of Microbiology, Quaid-i-Azam University, Islamabad, Pakistan</em><br />
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<p style="text-align: justify;"><strong>Abstract</strong></p>
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Newcastle disease (ND) is a contagious viral disease of many avian species particularly domestic poultry, and is responsible for devastating outbreaks in the poultry industries around the globe. In spite of its importance and endemicity in Southern Asia, data on the genetic nature of the viruses and epizootiological information of the disease is scarce. In this study, six isolates from an emerging wave of ND outbreaks in the north of Pakistan and two isolates from healthy poultry flocks were biologically and genetically characterized. Based on pathogenicity indices such as intracerebral pathogenicity index (ICPI), mean death time (MDT) and cleavage motifs in the fusion protein, all these isolates were classified as virulent. Phylogenetic analysis of the fusion (F), hemagglutinin-neuraminidase (HN) and matrix (M) genes indicated the emergence of a novel genetic group within lineage 5, distinct from isolates previously reported in the region. Several mutations in the neutralizing epitopes and functionally important motifs of the F and HN genes pose a need for re-evaluation of the currently used vaccine and vaccination practices. The characteristics of Newcastle disease virus (NDV) as virulent (F protein cleavage site, ICPI and MDT) in apparently healthy backyard poultry (BYP) explain that BYP can play crucial role in the epizootiology and spread of the disease. The present investigation provides essential information on the genetic nature of NDV circulating in Pakistan and its implication on disease diagnosis and control. Furthermore, these investigations emphasize the importance of continuous surveillance of ND in developing countries.</p>
<p style="text-align: justify;"><strong>Keywords:</strong> Newcastle disease, Pakistan, Poultry, Sequencing, Phylogenetic analysis</p>