ABSTRACT
BACKGROUND: Virulent Newcastle disease virus (vNDV) causes great economic losses to the poultry industry throughout the world. Despite the endemicity of Newcastle disease (ND) and occurrence of recurrent outbreaks, the nature and genetic features of circulating NDV strains in Iran are largely unknown. Aims: This study was conducted to characterize 13 NDV isolates obtained from different outbreaks in various regions of Iran during 1999-2000 by sequencing and phylogenetic analysis of complete coding sequences of haemagglutinin-neuraminidase (HN) gene. METHODS: All isolates were analyzed based on the previously determined in vivo pathogenicity indices and amino acid (aa) sequences of fusion (F) protein cleavage site (FPCS). RESULTS: Phylogenetic analysis based on the HN gene coding region revealed a very close relationship of these viruses with the recently defined genotype XIII, and more specifically, subgenotype XIIIa viruses. Analysis of HN gene nucleotide (nt) sequences revealed that all studied isolates encode for a protein length of 571 aa and there is no C-terminal extension on HN aa sequences. Sequence analysis revealed multiple aa residue substitutions at antigenic sites or neutralizing epitopes on the HN glycoprotein of studied viruses compared with commonly used vaccinal strains. CONCLUSION: In this study, molecular characterization of vNDV isolates, obtained from commercial poultry farms in Iran, were conducted through complete sequencing and analysis of HN gene. Isolation and molecular characterization of further NDV isolates from other parts of Iran and from neighboring countries in the region will be helpful to identify the nature and origin of indigenous viruses.
ABSTRACT
Pigeons are considered as one of the major natural reservoirs in the epidemiology of Newcastle disease (ND). In this study, the partial sequence of fusion protein gene of 17 pigeon-origin ND viruses (NDVs) isolated during 2012-2013 in Iran was analysed. Since the studied isolates showed F0 protein cleavage sites compatible with velogenic NDVs, all were considered as virulent NDVs. Two isolates carried 112RRQKRF117 as the cleavage site motif, whereas the rest demonstrated 112KRQKRF117 motif which just recently has been reported among Iranian virulent NDVs. Phylogenetic analysis divided all these diverse isolates in two distinct clusters within class II genotype VI. Based on the partial fusion protein gene sequence, 15 out of 17 isolates showed the highest genetic identity to subgenotype VIb/2 and the other two isolates were placed in a distinct genetic group of genotype VI. Based on recent findings, at least two different sublineages of genotype VI are causing the ND outbreaks in the pigeon population and are circulating simultaneously along with virulent NDVs of genotype VII in various species in Iran. The continuing circulation of a diverse group of virulent NDVs as an enzootic in widespread species such as pigeon can cause outbreaks in commercial poultry flocks and also failure in controlling programmes. Therefore, the constant monitoring and awareness of the virus characteristics should be considered in controlling programmes against ND in Iran.
