Consequences of Transstadial Transmission on Tick-borne Virus Genetic Diversity

 描述(申请人提供)：目前节肢动物传播病毒(虫媒病毒)进化的范式是权衡假说，该假说认为不同脊椎动物和无脊椎动物宿主之间的循环对虫媒病毒的遗传变化提出了显著的限制。研究蚊媒病毒中的这些限制因素使人们对流行性疾病和病毒出现有了新的理解。然而，权衡假说是基于蚊媒病毒的，并被认为对扁虱传播的病毒也是正确的。这代表了该领域的一个关键差距，因为扁虱传播病毒和蚊媒病毒的传播周期在关键特征上不同，这些特征对病毒的永久传播起着重要作用，例如垂直传播和经性病传播。在扁虱传播的病毒中，克里米亚-刚果出血热病毒(CCHFV)是导致严重和致命人类疾病的最广泛的原因，每年有数千例病例。由于缺乏疫苗、高死亡率和可能对公共卫生造成重大影响，NIAID最近将CCHFV提升为A类优先病原体。与其他虫媒病毒相比，CCHFV在不同毒株之间显示出非凡的遗传多样性。它的多样性与人类毒力的增加和新环境中的出现有关，并阻碍了诊断工具和对策的开发。最近，我们利用边缘透明线虫(主要载体)和小鼠建立了CCHFV在BSL4中的第一个实验性传播模型。通过使用下一代测序，我们在CCHFV中检测到大量的非同义突变，这些突变仅在一次经肠道传播后从扁虱中恢复。在从哺乳动物宿主获得的CCHFV中未检测到高突变频率。这些发现与权衡假说相矛盾，并表明在扁虱中CCHFV的选择压力比之前预期的更大。根据这些数据，我们假设通过TICK载体的经途径传播是CCHFV遗传多样性的主要决定因素，而蜕皮阶段是扩大CCHFV宿主内多样性的关键过程。目的1将分析CCHFV在多次传播和传播到哺乳动物宿主后的变异和病毒多样性，以表征CCHFV随时间的选择压力。AIM 2将跟踪CCHFV在蜕皮期间在扁虱中的传播，以确定潜在的病毒扩展热点，并了解经肠道传播如何导致宿主内更大的多样性。这些研究产生的信息将使我们对形成这种新兴病毒基因组多样性的扁虱-病毒-宿主相互作用有一个新的理解，并将导致 从壁虱传播病毒的角度对权衡假说进行重新评估。确定影响CCHFV遗传可塑性的因素对于了解病毒对不断变化的环境的适应以及确定病毒逃避载体和宿主免疫反应将是重要的。

 DESCRIPTION (provided by applicant): The current paradigm for evolution of arthropod-borne viruses (arboviruses) is the trade-off hypothesis, which proposes that cycling between different vertebrate and invertebrate hosts, presents significant constraints on genetic change of arboviruses. Studying these constraints in mosquito-borne viruses has led to a new understanding of epizootics and virus emergence. However, the trade-off hypothesis was based on mosquito- borne viruses and is assumed to be correct for tick-borne viruses too. This represents a critical gap in the field because the transmission cycles of tick-borne versus mosquito-borne viruses differ in key features that play a major role in virus perpetuation, such as vertical and transstadial transmission. Among the tick-borne viruses, Crimean-Congo hemorrhagic fever virus (CCHFV) is the most widespread cause of severe and fatal human disease with thousands of cases annually. The NIAID has recently promoted CCHFV to a Category A priority pathogen due to the lack of vaccines, high mortality rates, and potential for major public health impact. Compared to other arboviruses, CCHFV shows an extraordinary amount of genetic diversity among strains. Its diversity has been linked to increased virulence in humans and emergence in new environments and impedes diagnostic tool and countermeasure development. We recently established the first experimental transmission model for CCHFV in BSL4 by utilizing Hyalomma marginatum ticks (the main vector) and mice. By using next generation sequencing, we detected a significant number of non-synonymous mutations in CCHFV recovered from ticks after only a single transstadial transmission. The high mutation frequency was not detected in CCHFV obtained from the mammalian host. These findings are in contradiction to the trade-off hypothesis and suggested a greater selection pressure for CCHFV in the tick than previously expected. Given these data, we hypothesize that transstadial transmission by the tick vector is a major determinant of the genetic diversity of CCHFV, and the molting phase is the key process responsible for expanding CCHFV intra-host diversity. Aim 1 will analyze CCHFV mutations and viral diversity after multiple transstadial transmissions and transmission to the mammalian host to characterize the CCHFV selection pressure over time. Aim 2 will track CCHFV dissemination in the tick during molting to identify potential viral expansion hotspots and understand how transstadial transmission leads to greater intra-host diversity. The information generated from these studies will give us a new understanding of the tick-virus-host interaction that shapes the genomic diversity of this emerging virus, and will lead to a reevaluation of the trade-off hypothesis from a tick-borne virus perspective. Characterizing the forces that shape CCHFV genetic plasticity will be important in the understanding of virus adaptations to changing environments and in determining viral evasion of the vector and host immune response.