Full-length genome analysis of two genotype III velogenic Newcastle diseases virus strains reveals their close relationship with vaccine Mukteswar

Abstract:

Abstract：[Objective]The purpose of this research is trying to uncover the homology between two velogenic genotype III Newcastle disease virus (NDV) isolates with NDV strain Mukteswar, which was commonly used as vaccine in China. [Methods]The full-length genome of NDV isolates, JS/7/05/Ch and JS/9/05/Go, were determined by RT-PCR and then analyzed. [Results]The full-length genome of 2 genotype III velogenic NDV isolates shared 99.7% nucleotide identity with that of Mukteswar. The results of alignment of 6 viral genes showed that JS/7/05/Ch and JS/9/05/Go shared nucleotide and amino acid identities of 99.6 %～99.9% and 98.8%～99.8% with that of Mukteswar, respectively. Furthermore, the IVPI score of JS/7/05/Ch and JS/9/05/Go was 2.18 and 1.33, remarkablely higher than that of Mukteswar, while the 3 NDV strains shared the consensus cleavage site of virulent NDV strains (112RRQRRF117). Virulence of NDV is mainly determined by the amino acid sequence of the fusion (F) protein cleavage site, since host proteases that cleave the F protein of virulent strains are present in more tissues than those that cleave the F protein of lentogenic strains. However, 3 NDV strains with same F protein cleavage site showed different virulence. The entire genomic sequence of JS/7/05/Ch, JS/9/05/Go and Mukteswar was further analyzed. Three strains shared some gene-start signal, gene-end signal, intergenic region and six highly identical viral genes. Most amino acid differences among JS/7/05/Ch, JS/9/05/Go and Mukteswar were found in the predicted HN and L protein, and the predicted NP, P, V, W, M and even F protein had few amino acid differences. [Conclusion]First, it is concluded that field isolates JS/7/05/Ch and JS/9/05/Go are derived from Mukteswar and more attention must be paid to the virulence enhancement of vaccine strains. Second, it is proposed that the differences in the amino acid sequence of HN and L protein may give rise to the significant virulence differences between two NDV isolates and Mukteswar.