Molecular characterization and phylogenetic study of velogenic Newcastle disease virus isolates in Iran

The pathogenicity and genetic characterizations of six Newcastle disease virus (NDV) isolates obtained from chicken farms in six different regions in Iran were carried out using conventional and molecular techniques. Based on the pathogenicity indices (MDT, ICPI, and IVPI), all of these isolates were found to be velogenic (highly virulent) strains. A sequence analysis of the full-length mRNA encoding the fusion glycoprotein precursor (F-0) of the NDV's fusion proteins F-1 and F-2 in these six isolates showed the presence of point mutations in form of nucleic acid substitutions at positions 82((C -> T)), 83((T -> C)), 736((A -> G)), and 1,633((G -> A)). However, the nucleic acid residues at positions 330-347 of the precursor F-0 gene, corresponding to the cleavage site of the F-0 protein, were found to have remained conserved among the six NDV isolates. A phylogenetic comparison between the six Iranian isolates and the NDVs whose F-0 gene sequences were previously deposited in GenBank Database showed that all of the newly characterized Iranian NDV isolates belonged to genotype VII.