![]() ![]() NDV is a continuously evolving virus, with evidence of extremely rapid evolution of virulent strains. ĭespite extensive vaccination and strict biosecurity measures, ND outbreaks are prevalent in both vaccinated and non-vaccinated flocks. The velogenic strain can be further divided into viscerotropic velogenic and neurotropic velogenic strains. Also, the severity of the disease in hosts can be used to classify NDV into three pathotypes: lentogenic, mesogenic, and velogenic. ![]() Virulent NDV strains (vNDV) have a cleavage site with polybasic amino acids at the C-terminus of the F2 protein with pattern 112RRQK/RR 116 and phenylalanine (F) at the N-terminus of the F1 protein (residue 117). The F protein, and more specifically the amino acid sequence of its cleavage site, is known to be a key determinant of NDV pathogenicity. Reportedly, PPMV-1 isolates with MDT ranging from 62.4 to 79.2 h are considered as mesogenic, , ]. The key characteristics determining NDV virulence are mean death time (MDT), intracerebral pathogenicity index (ICPI), fusion (F) protein cleavage site motifs and hemagglutinin-neuraminidase (HN) protein. Class II viruses have been found in both domestic and wild birds worldwide, causing at least five ND panzootics. Class II NDV viruses are currently divided into 21 genotypes (I-XXI), some of which have multiple sub-genotypes. Class I viruses have a single genotype and three sub-genotypes (1.1.1 (former 1a), 1.1.2 (former 1b), and 1.2 (former 1c and 1d)), are mostly avirulent, and have primarily been found in waterfowl and shorebirds. Genetically, Newcastle disease virus (NDV) isolates are divided into two main groups: class I and class II based on their full-length F-gene coding sequences. It is a single-stranded, non-segmented, negative-sense enveloped RNA virus with a genome of about 15.2 kb pairs. ![]() Both APMV-1 and PPMV-1 virus belong to the Avulavirus genus, the Paramyxoviridae family, and the Mononegavirales order. Newcastle disease is caused by Avian paramyxovirus type 1 (APMV-1) and in pigeons the virus is known as pigeon paramyxovirus type 1 (PPMV-1), which represents a variant of APMV-1, , ]. In conclusion, genotype XXI.1.2 NDVs are circulating in the pigeon population of Bangladesh since 1990s, produce high mortality in pigeons with pneumonia, hepatocellular necrosis, renal tubular degeneration, and neuronal necrosis in pigeons, and may infect chickens without overt signs of clinical disease and are likely to shed viruses via the oral or cloacal routes.Īccording to the World Organization for Animal Health (WOAH), Newcastle disease (ND), is amongst the most important poultry diseases around the world, affecting a wide range of species including chickens, pigeons, and at least 239 other bird species. qRT-PCR revealed the replication of the virus in both pigeons and chickens however, higher viral RNA loads were observed in oropharyngeal and cloacal swabs, respiratory tissues, and spleen of infected pigeons than the chickens. In contrast, only slight congestion was found in lungs of the infected chickens. Histologically, consolidation in the lungs with collapsed alveoli and edema around the blood vessels, hemorrhages in the trachea, severe hemorrhages and congestion, focal aggregation of mononuclear cells, and single hepatocellular necrosis in the liver, severe congestion, multifocal tubular degeneration, and necrosis, as well as mononuclear cell infiltration in the renal parenchyma, encephalomalacia with severe neuronal necrosis with neuronophagia were noticed in the brain in infected pigeons. The infected pigeons showed extensive and systemic lesions including hemorrhagic and/or vascular changes in the conjunctiva, respiratory and digestive system and brain, and atrophy in the spleen, while only mild congestion in the lungs was noticed in the inoculated chickens. Experimental infection of chickens and pigeons revealed no or minimum clinical signs in chickens, while a relatively high morbidity (70%) and mortality (60%) were observed in pigeons. Pathogenicity testing using mean embryo death time pathotyped the viruses as mesogenic, while all isolates carried multiple basic amino acid residues at the fusion protein cleavage site. The Bayesian Markov Chain Monte Carlo analysis revealed that the ancestor of Bangladeshi pigeon NDVs and the viruses from sub-genotype XXI.1.2 existed in the late 1990s. Molecular phylogenetic analysis based on the complete fusion gene sequences classified the three study isolates into genotype XXI (sub-genotype XXI.1.2) together with recent NDV isolates obtained from pigeons in Pakistan (2014–2018). Here, we performed molecular and pathogenic characterization of a Newcastle disease virus (NDV) isolate from pigeons in Bangladesh.
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