Abstract
Two velogenic Newcastle disease viruses (NDV) obtained from outbreaks in domestic ducks in China were characterized in this study. Phylogenetic analysis revealed that both strains clustered with the class II viruses, with one phylogenetically close to the genotype VII NDVs and the other closer to genotype IX. The deduced amino acid sequence of the cleavage site of the fusion (F) protein confirmed that both isolates contained the virulent motif 112RRQK/RRF117 at the cleavage site. The two NDVs had severe pathogenicity in fully susceptible chickens, resulting in 100% mortality. One of the isolates also demonstrated some pathogenicity in domestic ducks. The present study suggests that more than one genotype of NDV circulates in domestic ducks in China and viral transmission may occur among chickens and domestic ducks.
Highlights
Newcastle disease virus (NDV) belongs to genus Avulavirus in the family Paramyxoviridae and has been designated as avian paramyxovirus 1 [1]
NDV strains are classified as high virulence, intermediate or low virulence based on some biological parameters, such as the mean death time (MDT) of chicken embryos infected with the minimum lethal dose of virus, the intracerebral pathogenicity index (ICPI) in 1-day-old chicks and the intravenous pathogenicity index (IVPI) in 6-week-old chickens
The prevailing NDV strains have significant differences from the current vaccine strains in their biology, serology and genetics, which might be considered as reasons for the outbreaks [2,22,28,30]
Summary
Newcastle disease virus (NDV) belongs to genus Avulavirus in the family Paramyxoviridae and has been designated as avian paramyxovirus 1 [1]. Two nonstructural proteins (V and W) may be generated due to an mRNA-editing event in which one (V) or two (W) G residues are inserted at a specific position within the P gene mRNA [3,4]. NDV strains are classified as high virulence (velogenic), intermediate (mesogenic) or low virulence (lentogenic) based on some biological parameters, such as the mean death time (MDT) of chicken embryos infected with the minimum lethal dose of virus, the intracerebral pathogenicity index (ICPI) in 1-day-old chicks and the intravenous pathogenicity index (IVPI) in 6-week-old chickens. The mesogenic strains cause moderate respiratory signs with occasional nervous signs while the lentogenic strains typically cause subclinical infections or mild respiratory disease [5,6,7]. The molecular basis for NDV pathogenicity is dependent on the cleavability of precursor F (F0) to active F1 and F2 polypeptides by cellular proteases [2,8]
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