Determinants of Usutu virus bird-to-mosquito transmission

项目摘要 西尼罗河病毒(WNV)、圣路易斯脑炎病毒(SLEV)和Usutu病毒(USUV)关系密切 蚊媒病毒会导致人类神经侵袭性疾病。所有这三种病毒都在 重叠的鸟类/蚊子周期，对人类产生溢出效应。西尼罗河病毒于1999年引入美国 由于禽类的交叉免疫反应，迅速取代了以前循环的SLEV。然而，a 最近在美国出现了SLEV的新基因，导致2015年爆发，我们发现 在体外，WNV在禽类中的免疫反应不能中和新的SLEV基因。USUV最近出现 在欧洲，它至少从非洲引进了三次。我们发现了家麻雀 (Passer Home Ticus)和致倦库蚊(Culex Ququiefasciatus)对西NV和SLEV有很强的抵抗力 也容易受到USUV的影响。这个项目的长期目标是了解影响小说的因素 黄病毒的出现，以便预测在人类中的爆发。这项研究的目标是确定 合格的北美鸟类和蚊子对USUV和确定西尼罗河病毒免疫的作用 在SLEV和USUV上出现的鸟类。假设是新的SLEV基因和USUV具有 由于有能力在北美建立或有可能建立传播周期 当地禽鸟和蚊子以及禽类对西尼罗河病毒免疫的逃避，从而导致患上西尼罗病毒的风险增加 人类的神经侵袭性疾病。两个具体的目标将解决这一假设：1)确定诺斯 美国鸟类和蚊子对USUV有能力；2)评估以前 暴露于西尼罗河病毒对SLEV和USUV感染禽类。在第一个目标中，我们将捕获三种野鸟 以确定当地鸟类对USUV的易感性。我们将量化USUV的感染阈值 通过在受感染的禽类上喂食蚊子，然后在感染的禽类身上检测传染性病毒，从而实现鸟与蚊子之间的传播 受感染蚊子的唾液。在第二个目标中，西尼罗河病毒预暴露对后续工作的影响 新的SLEV基因和USUV的感染将在禽类中进行评估。接种过的禽类的血清将被 测试对所有三种病毒的体外中和活性，以确定诊断能力 用血清学鉴定黄病毒感染。这里提出的研究是创新的，因为它 使用一种新的禽类研究了一种新的SLEV基因型和USUV，它们是被忽视的新兴病毒 实验模型。在成功完成拟议的研究后，这项研究的预期贡献 工作将是确定USUV水库和病媒种类以及影响地方病的因素 SLEV和USUV的变速器。这一贡献预计将是重大的，因为理解 新出现的黄病毒的传播周期将导致预测人类疾病的能力。

Project Summary West Nile virus (WNV), St. Louis encephalitis virus (SLEV), and Usutu virus (USUV) are closely-related mosquito-borne viruses that cause neuroinvasive disease in humans. All three viruses are maintained in overlapping bird/mosquito cycles, with spillover to humans. The introduction of WNV into the U.S. in 1999 quickly displaced the previously-circulating SLEV due to cross-reactive immune responses in birds. However, a novel genotype of SLEV recently emerged in the U.S., causing an outbreak in 2015, and we have found that WNV immune responses in birds do not neutralize the novel SLEV genotype in vitro. USUV recently emerged in Europe, where it has been introduced at least three times from Africa. We have found that House sparrows (Passer domesticus) and Culex quinquefasciatus mosquitoes, which are competent for WNV and SLEV, are also susceptible to USUV. The long-term goal of this project is to understand the factors that influence novel flavivirus emergence in order to predict outbreaks in humans. The objectives of this study are to identify competent North American avian and mosquito species for USUV and to determine the role of WNV immunity in birds on SLEV and USUV emergence. The hypothesis is that the novel SLEV genotype and USUV have established or have the potential to establish transmission cycles in North America due to the competence of local birds and mosquitoes and the evasion of WNV immunity in birds, thus leading to an increased risk of neuroinvasive disease in humans. Two specific aims will address this hypothesis: 1) Determine whether North American passerines and mosquitoes are competent for USUV; and 2) Assess the influence of previous exposure to WNV on SLEV and USUV infection in birds. In the first aim, we will trap three species of wild birds to determine the susceptibility of local birds to USUV. We will quantify the infectious threshold of USUV for bird-to-mosquito transmission by feeding mosquitoes on infected birds and then measure infectious virus in the expectorate of infected mosquitoes. In the second aim, the effect of WNV pre-exposure on subsequent infection by the novel SLEV genotype and USUV will be evaluated in birds. Sera from inoculated birds will be tested for in vitro neutralizing activity against all three viruses to determine the capacity for diagnostically identifying flavivirus infections using serology. The research proposed here is innovative because it investigates a novel SLEV genotype and USUV, which are neglected, emerging viruses, using a novel avian experimental model. Upon successful completion of the proposed research, the anticipated contribution of this work will be the identification of USUV reservoir and vector species and factors that influence enzootic transmission of SLEV and USUV. This contribution is expected to be significant because understanding the transmission cycle of emerging flaviviruses will lead to the ability to predict disease in humans.