Introduction of a Newcastle disease virus challenge strain (sub-genotype VII.۱.۱) isolated in Iran

Newcastle disease virus (NDV) sub-genotype VII.۱.۱ is the most common circulating NDV in Iran. In this study, a velogenic NDV isolate was plaque purified and then characterized according to Office International des Epizooties (OIE) standard protocols. The biological properties of the purified isolate named CH/RT۴۰/IR/۲۰۱۱ were characterized using sequencing and phylogenetic analysis, measurement of pathogenicity indexes and challenge studies. The isolate was plaque purified on chicken embryo fibroblast cells for three rounds and then characterized using molecular and biological approaches. Phylogenetic and evolutionary distance analysis of fusion and hemagglutinin-neuraminidase genes classified the virus in sub-genotype VII.۱.۱. No mutation was observed in the glycosylation and neutralizing epitope sites of the fusion and hemagglutinin-neuraminidase proteins compared to other reported Iranian NDV VII.۱.۱ isolates. The presence of the ۱۱۲RRQKRF۱۱۷ motif in the fusion protein cleavage site together with mean death time, intracerebral pathogenicity index and intravenous pathogenicity index of ۵۷ hr, ۱.۸۰ and ۲.۵۰ respectively, revealed that the RT۴۰ isolate was a velogenic NDV. In the challenge study, all chickens were inoculated via eye drop, and intranasal route with RT۴۰ isolate died within a week. While all chickens in the vaccinated and challenged group survived and showed no clinical signs. In conclusion, according to genetic analysis, pathotyping and challenge study, the RT۴۰ isolate was similar to virulent NDVs in Iran and was a suitable candidate for a national standard challenge strain, vaccine trials and vaccine production in commercial levers.

Keywords:

Challenge strain , Fusion gene , Hemagglutinin-neuraminidase gene , Newcastle disease virus , Sub-genotype VII.۱.۱