Generation by reverse genetics of an effective attenuated Newcastle disease virus vaccine based on a prevalent highly virulent Chinese strain

To investigate whether the differences between the circulating Newcastle disease virus (NDV) isolates and the used vaccine might account for the current ND outbreaks in vaccinated poultry flocks. A reverse genetics system using prevalent genotype VIId isolate SG10 was constructed and a mutant virus, named aSG10, was developed by changing the virulent F protein cleavage site motif "(112)RRQKRa dagger"F-117" into an avirulent motif "(112)GRQGRa dagger"L-117". The attenuated pathogenicity of aSG10 was confirmed from the mean death time and intracerebral pathogenicity index. aSG10 and LaSota both protected vaccinated birds from death after challenge with highly virulent genotype VII NDV, strain SG10. However, aSG10 significantly reduced the challenge virus shedding from the vaccinated birds compared to LaSota vaccine. We also generated a recombinant virus, aSG10-enhanced green fluorescent protein (EGFP), which expresses EGFP. aSG10-EGFP stably expressed EGFP for at least 10 passages. The mutant, aSG10, can be safely used as a vaccine vector and is a potential vaccine candidate in increasing the protective efficacy for the control of current ND epidemic in China.