Genetic determinants of adaptation of two flaviviruses

描述(申请人提供)：西尼罗河病毒(西尼罗河病毒；黄病毒科；黄病毒)在整个西半球的出现和迅速的生物地理扩张，以及其他具有重要医学意义的病毒的重新出现，突显了美国对新的和重新出现的病毒病原体的脆弱性。为了了解人畜共患病病毒在引入新的栖息地后如何进化，有必要解决形成病毒适应的选择压力。具体地说，我们必须确定在决定病毒种群与不同宿主相互作用的可塑性(单个基因型对许多宿主通用的能力)和适应性(快速产生更合适的基因型的能力)方面的重要因素，以便评估地理扩展到新环境的能力。解释一种病毒在新环境中成功定居的机制的特征很差。在自然相关宿主上的实验研究通常缺乏病毒适应研究。这些研究需要为适应性提供合理和相关的机制解释。拟议的研究将通过使用自然和生态相关的蚊子和鸟类宿主进行的实验室研究，解决知识状况的这一根本差距。实验室研究是对影响病毒适应的因素进行系统评估的最佳方式。我们选择与两种黄病毒，西尼罗河病毒和圣路易斯脑炎病毒(SLEV)进行比较研究。这两种病毒在抗原性、基因和结构上都非常接近。然而，近年来，它们在西半球的流行模式有很大不同。西尼罗河病毒不断扩大其宿主和地理范围，自它出现以来，每年在美国都会产生大量的疾病。另一方面，SLEV只表现出相对受控的周期性暴发。西尼罗河病毒在北美的活动是否最终会模仿SLEV的活动仍有待观察，但对当前基因类型的比较研究应该阐明定义可变流行病学模式的遗传相关性。我们实验室最近的实验研究表明，SLEV和WNV在体外适应方面存在明显差异。我们广泛的BSL-3实验室、昆虫和间隔室将使我们能够在自然宿主体内确认和扩大体外结果，并进一步表征在不同宿主和新环境中限制和促进虫媒病毒活动的重要因素。据我们所知，这些是利用自然脊椎动物和蚊子宿主来阐明病毒适应机制的首批研究之一。 公共卫生相关性：我们选择与两种黄病毒--西尼罗河病毒和圣路易斯脑炎病毒(SLEV)进行比较研究。我们实验室最近的实验研究表明，SLEV和WNV在体外适应方面存在明显差异。我们广泛的BSL-3实验室、昆虫和间隔室将使我们能够在自然宿主体内确认和扩大体外结果，并进一步表征在不同宿主和环境中限制和促进虫媒病毒活性的重要因素。

DESCRIPTION (provided by applicant): The emergence and rapid biogeographic expansion of West Nile Virus (WNV; Flaviviridae; Flavivirus) throughout the western hemisphere, as well as the re-emergence of other medically significant viruses, highlight the vulnerability of the United States to both novel and reemerging viral pathogens. To understand how zoonotic viruses evolve following introduction to new habitats, it is necessary to address the selective pressures shaping viral adaptation. Specifically, we must characterize factors important in determining the plasticity (ability of individual genotypes to generalize to many hosts) and adaptability (ability to rapidly produce fitter genotypes) of virus populations interacting with different hosts in order to evaluate the capacity for geographic expansion into new environments. The mechanisms that account for success of a virus in colonization of new environments are poorly characterized. Experimental studies in naturally relevant hosts are generally lacking in virus adaptation studies. These studies are required to provide plausible and relevant mechanistic explanations for adaptability. The proposed research will address this fundamental gap in the state of knowledge through laboratory studies using natural and ecologically relevant mosquito and avian hosts. Studies in the laboratory are the best way to conduct a systematic evaluation of the factors that influence viral adaptation. We have chosen to undertake a comparative study with two flaviviruses, WNV and St. Louis encephalitis virus (SLEV). These two viruses are very closely related antigenically, genetically, and structurally. Nevertheless, their epidemiological patterns in the western hemisphere have differed strongly in recent years. WNV has continued to expand both its host and geographic ranges, producing significant levels of disease in the U.S. every year since its emergence. SLEV, on the other hand, exhibits only periodic outbreaks which remain relatively contained. Whether WNV activity in North America will ultimately mimic that of SLEV remains to be seen, but a comparative study of current genotypes should elucidate genetic correlates which define variable epidemiological patterns. Recent experimental studies in our laboratory have revealed apparent differences in in vitro adaptation between SLEV and WNV. Our extensive BSL-3 laboratory, insectary, and vivarium will allow us to confirm and expand the in vitro results in vivo in natural hosts and further characterize important factors that both constrain and facilitate arbovirus activity in disparate hosts and new environments. These are among the first studies, to the best of our knowledge, using natural vertebrate and mosquito hosts to elucidate mechanisms of viral adaptation. PUBLIC HEALTH RELEVANCE: We have chosen to undertake a comparative study with two flaviviruses, WNV and St. Louis encephalitis virus (SLEV). Recent experimental studies in our laboratory have revealed apparent differences in in vitro adaptation between SLEV and WNV. Our extensive BSL-3 laboratory, insectary, and vivarium will allow us to confirm and expand the in vitro results in vivo in natural hosts and further characterize the important factors that both constrain and facilitate arbovirus activity in various hosts and environments.