上海兽医所发现新城疫病毒毒力演化新机制
近日，从中国农业科学院上海兽医研究所获悉，该所水禽病毒病创新团队发现，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。相关结果近期在线发表于的著名国际学术期刊《病毒学杂志（Journal of Virology）》上。据该团队首席科学家丁铲研究员介绍，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。
【标题】：Evolution of Newcastle Disease Virus Quasispecies Diversity and Enhanced Virulence after Passage through Chicken Air Sacs
【作者】：Meng, C.; Qiu, X.; Yu, S. (...)
【来源】：J Virol, 2015, 90(4), 2052-2063
【摘要】：It has been reported that lentogenic Newcastle disease virus (NDV) isolates havethe 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 sacs. The velogenic properties of this selected variant were determined using mean death time (MDT) assays, intracerebral pathogenicity index (ICPI), the intravenous pathogenicity index (IVPI), histopathology, and the analysis of host tissue tropism. In 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 tobe nearly identical, suggesting that both JS10-A10 and JS10-E20 were directly generated from JS10. To investigate the mechanism for virulence enhancement, thepartial genome covering the F0 cleavage site of JS10 and its variants were analyzed using ultradeep pyrosequencing (UDPS) and the proportions 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. IMPORTANCE:An avirulent isolate, JS10, was passaged through chicken air sacs and embryos, and the pathogenicity of the variants was assessed. A virulent variant, JS10-A10, was generated from consecutive passage in air sacs. We developed a deep-sequencing approach to detect low-frequency viral variants across the NDV genome. We observed that virulence enhancement of JS10 was due to the selective accumulation of velogenic quasispecies and the concomitant disappearance of lentogenic quasispecies. Our results suggest that because it is difficult to avoid contact between natural waterfowl reservoirs and sensitive poultry operations, circulating lentogenic NDV strains may represent a potential reservoir for emergent velogenic NDV strains that could cause outbreaks in chickens.
http://www.ncbi.nlm.nih.gov/pubmed/26656697?dopt=Abstract 谢谢分享
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