Abstract
BackgroundNewcastle disease (ND) is one of the most deadly diseases of poultry around the globe. The disease is endemic in Pakistan and recurrent outbreaks are being reported regularly in wild captive, rural and commercial poultry flocks. Though, efforts have been made to characterize the causative agent in some of parts of the country, the genetic nature of strains circulating throughout Pakistan is currently lacking.Material and methodsTo ascertain the genetics of NDV, 452 blood samples were collected from 113 flocks, originating from all the provinces of Pakistan, showing high mortality (30–80%). The samples represented domesticated poultry (broiler, layer and rural) as well as wild captive birds (pigeons, turkeys, pheasants and peacock). Samples were screened with real-time PCR for both matrix and fusion genes (1792 bp), positive samples were subjected to amplification of full fusion gene and subsequent sequencing and phylogenetic analysis.ResultsThe deduced amino acid sequence of the fusion protein cleavage site indicated the presence of motif (112RK/RQRR↓F117) typical for velogenic strains of NDV. Phylogenetic analysis of hypervariable region of the fusion gene indicated that all the isolates belong to lineage 5 of NDV except isolates collected from Khyber Pakhtunkhwa (KPK) province. A higher resolution of the phylogenetic analysis of lineage 5 showed the distribution of Pakistani NDV strains to 5b. However, the isolates from KPK belonged to lineage 4c; the first report of such lineage from this province.ConclusionsTaken together, data indicated the prevalence of multiple lineages of NDV in different poultry population including wild captive birds. Such understanding is crucial to underpin the nature of circulating strains of NDV, their potential for interspecies transmission and disease diagnosis and control strategies.
Highlights
Phylogenetic analysis of hypervariable region of the fusion gene indicated that all the isolates belong to lineage 5 of Newcastle disease virus (NDV) except isolates collected from Khyber Pakhtunkhwa (KPK) province
A higher resolution of the phylogenetic analysis of lineage 5 showed the distribution of Pakistani NDV strains to 5b
Taken together, data indicated the prevalence of multiple lineages of NDV in different poultry population including wild captive birds
Summary
Newcastle disease is caused by avian paramyxovirus serotype-1 (APMV-1), which is known as Newcastle disease virus (NDV). NDV is classified in the genus Avulavirus within subfamily Paramyxovirinae, family Paramyxoviridae and order Mononegavirales [1] This enveloped virus has a negativesense, non-segmented, single stranded RNA genome of 15186, 15192 or 15198 nucleotides in length [1,5,6]. Clinical manifestation or severity of the ND depends largely upon the isolates involved in disease outbreak [1,2] Based upon pathogenicity, these strains are commonly categorized into velogenic, mesogenic and lentogenic types [4]. The amino acid sequence in more virulent, velogenic and mesogenic strains is 112R/K-R-Q-R/K-R↓F117 This sequence is cleavable by a variety of cellular proteases in various organs, resulting in wider systemic infection in respiratory system, gastro-intestinal tract and nervous system. Efforts have been made to characterize the causative agent in some of parts of the country, the genetic nature of strains circulating throughout Pakistan is currently lacking
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