An Attenuated Recombinant Newcastle Disease Virus of Genotype VII Generated by Reverse Genetics.

Genotype VII Newcastle disease virus (NDV) has been confirmed as the predominant epidemic strain in China. Traditional vaccine strains fail to provide complete immune protection when challenged with an epidemic strain. NDV vaccines with phylogenetic relationships closer to those of the endemic viruses demonstrate improved protective efficacy in reducing viral shedding and transmission. This research seeks to develop attenuated vaccine strains that are specifically aligned with NDV genotype VII. A reverse genetics system for the genotype VII NDV HB strain was developed, successfully rescuing the attenuated recombinant virus aHB by substituting the fusion protein (F) cleavage site motif "112R-R-Q-K-R↓F117" with "112G-R-Q-G-R↓L117." Recombinant aHB virus attenuation was verified by assessing the mean death time (MDT) and intracerebral pathogenicity index (ICPI). The attenuated aHB strain demonstrated greater proliferation titers than did the virulent HB and rHB strains both in vivo and in vitro. Furthermore, the genome exhibited significant genetic stability even after 10 passages in chicken embryos. When challenged with the HB strain of NDV genotype VII, the aHB-inactivated vaccine provided 100% protection to chickens and effectively prevented viral shedding. These findings indicate that recombinant aHB may serve as an effective vaccine candidate.