新城疫病毒某水禽分离株经鸡体传代后由非致病型转变为速发型的研究

最近，一株无毒力的新城疫病毒（NDV）在鸡体内繁殖时，变成了强毒株，但致今尚未能证实，经鸡体传代的野生水禽新城疫病毒是否也具有变成速发型毒株的能力，为了通过实验证明从水禽中分离的非致病型NDV可以转变为速发型病毒，我们通过在鸡体内传播鹅源性无毒力株，经气囊接种连续传代9次，随后再在鸡脑内传代5次，结果显示，该病毒的毒力变得很强，致死率可达100%，通过致病性试验证实，其具有典型的速发型病毒特征；融合蛋白裂解位点的序列分析表明，原始的分离株含有无毒力型毒株共有的裂解序列；E-R-Q-E-R/L，而通过鸡体反复传代后，该序列变为致癞 性毒株共有的序列：K-R-Q-K-R/F，这些结果表明，野生水禽中自然存在的无毒力毒株，具有无毒力株相应的序列，但当其在鸡群中传播时，则具有变成高致病性病毒的能力，同时研究表明，鸡体提供了该病毒从非致病型向致病型转变的选择机制。

Generation of Velogenic Newcastle Disease Viruses from a Nonpathogenic Waterfowl Isolate by Passaging in Chickens

A benign Newcastle disease virus (NDV) recently became highly virulent during replication in domestic chickens. It is still unclear whether NDVs circulating among wild waterfowl also have the potential to become highly pathogenic (velogenic) in chickens. To demonstrate experimentally the generation of velogenic NDV from a nonpathogenic waterfowl isolate, we passaged an avirulent goose isolate in chickens. After nine consecutive passages by air sac inoculation, followed by five passages in chick brain, the virus became highly virulent in chickens, producing a 100% mortality, and demonstrating typical velogenic properties in pathogenicity tests. Sequence analysis at the fusion protein cleavage site showed that the original isolate contained the typical virulent type:K-E-Q-E-R/L, which progressed incrementally to a typical virulent type, K-R-Q-K-R/F, during repeated passages in chickens. These results demonstrate that avirulent viruses, maintained in wild waterflow in nature and bearing the consensus avirulent type sequence, have the potential to become velogenic after being transmitted to and circulating in chicken populations. The results also suggest that chickens provide a mechanism for the selection of virulent viruses from an avirulent background.