近日，著名国际学术期刊《JouRNAl of Virology》上在线发表中国农业科学院上海兽医研究所水禽病毒病创新团队丁铲研究员的一项研究论文，文章指出来自家养水禽的弱毒新城疫病毒在鸡的气囊中连续传代后，通过准种的体内自然选择，进化为对鸡高致病性的强毒，此发现为动物传染病预警预报提供了重要借鉴。
丁铲研究员介绍，新城疫是一种急性高度致死性的烈性传染病，给世界养禽业带来严重的经济损失，是国际兽疫局(OIE)规定的必须上报疫病。然而，自然界野生鸟类存在的大量天然弱毒株，一定程度已成为我国养禽业的潜在威胁。
该团队经过数年攻关，将分离自鸭群的新城疫天然弱毒株分别经过鸡胚和雏鸡气囊连续传代，获得一系列变异株，生物学特性测定表明毒株之间的毒力差异显著，但基因组序列却几乎相同。随后对病毒融合蛋白位点F0进行高通量测序，经生物信息学分析发现变异株之间仅在数个氨基酸之间有变化，且不同的病毒序列以典型的准种形式共存于一株病毒中，但比例有明显差异。这些准种在易感鸡体内的复制速率差异很大，强毒准种要比弱毒准种快约80-100倍，通过自然选择，逐渐实现了强毒准种对弱毒准种的替代，从而导致鸡的临床发病。
这项研究成果揭示了病毒的准种形式在新城疫病毒毒力演化中的作用，同时为新城疫流行病学监测方法提供了新的思路。
原文链接：
evolution of Newcastle disease virus quasispecies diversity and enhanced virulence after passage through chicken air sacs
原文摘要：
It has been reported that lentogenic Newcastle disease virus (NDV) isolates have the potential to become velogenic after their transmission and circulation in chickens, but the underlying mechanism is unclear. In this study, a highly velogenic NDV variant, JS10-A10, was generated from the duck-origin lentogenic isolate JS10 through 10 consecutive passages in chicken air sac. The velogenic properties of this selected variant was determined using mean death time (MDT) assays, intracerebral pathogenicity indices (ICPI), the intravenous pathogenicity index (IVPI), histopathology, and the analysis of host tissue tropism. By contrast, JS10 remained lentogenic after 20 serial passages in chicken eggs (JS10-E20). The JS10, JS10-A10, and JS10-E20 genomes were sequenced and found to be nearly identical, suggesting that both JS10-A10 and JS10-E20 were directly generated from JS10. To investigate the mechanism for virulence enhancement, the partial genome covering the F0 cleavage site of JS10 and its variants were analyzed using ultra-deep-pyrosequencing (UDPS) and the proportion of virulence-related genomes in the quasispecies were calculated. Velogenic NDV genomes accumulated as a function of JS10 passaging through chicken air sacs. Our data suggest that lentogenic NDV strains circulating among poultry might be a risk factor to future potential velogenic NDV outbreaks in chickens.
http://www.bio1000.com/gnjz/immunology/505192.html
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