West Nile Viral Determinants of Avian Pathogenesis

描述（由申请人提供）：自1999年引入以来，西尼罗河病毒（WNV）已成为美国虫媒病毒性脑炎的主要病因。与西尼罗河病毒在北美迅速出现有关的最显著的流行病学因素是鸟类中病毒滴度高的发展和野生鸟类种群的死亡。尽管使用乌鸦死亡率作为西尼罗河病毒活动的哨兵，西尼罗河病毒在鸟类中致病性的潜在病毒遗传基础以及增加的鸟类毒力在西尼罗河病毒传播中的作用尚不清楚。在西尼罗河病毒禽库复制的基础上生成基础数据将填补我们在西尼罗河病毒传播知识方面的一个关键空白，并有助于改进现有的监测战略和预测出现模型，以预防人畜疾病。假设西尼罗河病毒在北美的出现是由于引入了一种能够有效复制禽类的新病毒基因型，这一假设将通过以下研究目标得到解决：(1)通过在禽强毒株和无毒株之间产生病毒嵌合体，确定导致乌鸦毒力差异的西尼罗河病毒遗传决定因素。由此产生的嵌合体将被测试其在乌鸦体内产生高病毒血症和发病率的能力，以及在体外复制系统中在高温下复制的能力。(2)阐明不同西尼罗河病毒在乌鸦发病机制上的差异，以确定禽类毒力差异背后的致病机制。组织趋向性、神经侵袭性和病毒持久性将与特定的遗传决定因素相关。蚊子的传染性将通过产生剂量感染模型来评估，该模型允许估计不同嵌合体对蚊子具有传染性的时间。(3)通过将先前确定的最小毒力决定因素整合到与禽类死亡率无关的替代西尼罗河病毒遗传主干中，评估出现替代西尼罗河病毒基因型的可能性。还将研究无毒西尼罗河病毒基因型对乌鸦的适应性，以衡量鸟类毒力选择作为北美西尼罗河病毒基因型出现的机制。关于病毒复制的作用和调节禽库内自然病毒种群毒力的机制的关键基本信息，将有助于更有效地实施疫苗接种规划和预测未来的西尼罗河病毒暴发。此外，病毒复制和发病机制的基础知识将为疫苗和抗病毒策略的开发提供见解。

DESCRIPTION (provided by the applicant): Since its introduction in 1999, West Nile virus (WNV) has become the leading cause of arboviral encephalitis in the United States. The most notable epidemiological factors associated with the rapid emergence of WNV in North America have been the development of high viral titers within birds and mortality among wild bird populations. Despite the use of crow mortality as a sentinel for WNV activity, the underlying viral genetic basis for WNV pathogenicity in birds and the role of increased avian virulence in the transmission of WNV are poorly understood. Generation of fundamental data on the basis of replication within the WNV avian reservoir will fill a critical gap in our knowledge of WNV transmission and aid in the improvement of existing surveillance strategies and predictive emergence models for the prevention of human and veterinary disease. The hypothesis that the emergence of WNV within North America has been the result of the introduction of a new viral genotype capable of efficient avian replication will be addressed with the following research aims: (1) Identify WN viral genetic determinants responsible for differential crow virulence through the generation of viral chimeras between avian virulent and avirulent WNV strains. The resulting chimeras will be tested for their ability to produce high viremia and morbidity within crows as well as replicate at elevated temperatures in an in vitro replication system. (2) Elucidate differences in crow pathogenesis between WNVs in order to identify the pathogenic mechanism(s) that underlie differential avian Virulence. Tissue tropism, neuro-invasion and viral persistence will be correlated with specific genetic determinants. Mosquito infectivity will be assessed through the generation of a dose-infection model, allowing for the estimation of the time to which different chimeras will be infectious to mosquitoes. (3) Assess the potential for the emergence of alternative WNV genotypes through the incorporation of the minimal virulence determinants previously identified into alternative WN viral genetic backbones that have not been associated with avian mortality. Adaptation of avirulent WNV genotypes to crows will also be investigated to gauge selection for bird virulence as a mechanism for the emergence of the North American WNV genotype. Critical basic information on the role of viral replication and mechanisms that modulate virulence in natural viral populations within avian reservoir will allow for more efficient implementation of an vaccination programs and the prediction of future WNV outbreaks. In addition, fundamental knowledge of viral replication and pathogenesis will provide insight for the development of vaccine and antiviral strategies.