中文摘要：

【目的】研究基因Ⅲ型新城疫（Newcastle disease，ND）强毒分离株JS／7／05／Ch和JS／9／05／Go与中等毒力疫苗株Mukteswar的亲缘性关系，分析三株新城疫病毒（Newcastle disease virus，NDV）的全基因差异。【方法】采用RT-PCR方法获得两株NDV分离株的全基因组核苷酸序列，与GenBank中公布的Mukteswar序列比对分析。【结果】强毒分离株与中等毒力疫苗株Mukteswar全基因组核苷酸同源性均为99.7％；病毒6个阅读框核苷酸序列与Mukteswar同源性为99.6％-99.9％；预测的8种病毒编码蛋白同源性在98.8％-99.8％。然而，测定MDT，ICPI和IVPI发现JS／7／05／Ch和JS／9／05／Go毒力明显强于Mukteswar，其中JS／7／05／Ch株的IVPI达到了2.18。【结论】综合3株NDV的遗传分析结果和已有的流行病学资料可以推断分离株JS/7／05／Ch和JS／9／05／Go是由疫苗株Mukteswar自然进化而来的返强毒株。因此，必须停止使用中等毒力疫苗以免造成更大的危害。

英文摘要：

[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.