The Evolutionary and Biological Bases of Host Switching in Viruses

描述（由申请人提供）：这个项目的总体目标是定义疾病出现过程的一个关键方面所涉及的进化步骤；病毒从一个宿主物种到另一个宿主物种的传播和随后的传播我们将使用比较分析来揭示病毒出现的不同阶段的长期系统发育模式，然后通过实验研究来揭示决定这些模式的潜在过程。我们将研究在不同动物系统内完成跨物种传播的两种不同病毒，其中既有供体宿主物种中的祖先病毒，也有来自受体宿主物种的新出现病毒，但它们对宿主病毒的适应程度不同；犬细小病毒（一种猫病毒的变种）的出现，以及H3N8流感病毒在马的跨物种传播后在犬类中出现。因此，这些研究将揭示涉及病毒出现的适应性过程，并对理解，更重要的是，预防此类事件具有广泛的意义。该项目的一个主要目的是检查与细小病毒出现有关的特定突变的适应性。本研究的第一部分将涉及全基因组序列数据的比较分析。然后，我们将确定在细小病毒出现的两个阶段中间病毒的适应性；首先是猫和最初的犬病毒之间的关系，其次是犬病毒在狗体内的适应性改进，这也导致了感染猫细胞的新能力。这些中间病毒提供了在跨物种传播过程中可能隐含的进化权衡的独特信息。这些病毒将在组织培养中测试其生存能力和其他生物学特性。在少数情况下，还将测试病毒在动物体内复制的能力。作为第二个主要目标，我们将研究病毒在其供体和受体宿主中复制时病毒序列的宿主内遗传多样性，例如狗的猫细小病毒（导致限制性胸腺感染）或狗的H3N8马流感病毒。我们将检查病毒在不同宿主中生长后发现的序列多样性的程度和结构，并使用比较序列分析来确定所见的变化是受到正面或负面选择压力的影响，还是仅仅反映了内在的突变谱。至关重要的是，我们还将分析病毒在经历一轮宿主-宿主传播后的多样性程度和结构，这可能会施加额外的和/或不同的选择压力。作为比较，我们还将使用细胞培养进行选择研究，在那里我们将测量细小病毒和流感病毒的抗体逃逸突变体的出现率，以及细小病毒的受体选择突变体

DESCRIPTION (provided by applicant): The overall goal of this project is to define the evolutionary steps involved in a key aspect of the process of disease emergence; the transmission and subsequent spread of viruses from one host species to another. We will use comparative analyses to reveal the long-term phylogenetic patterns of different stages of viral emergence, followed by experimental studies to reveal the underlying processes which determine these patterns. We will examine two different viruses which have accomplished cross-species transmission within different animal systems, where we have both the ancestral viruses in the donor host species and the emerged virus from the recipient host species, but which differ in their degree of host-virus adaptation; the emergence of the canine parvovirus as a variant of a virus of cats, and the emergence of H3N8 influenza virus in canines following cross-species transmission from horses. These studies will therefore reveal the adaptive processes involved in viral emergence and have broad implications for understanding, and more importantly, forestalling such events. A major aim of the project is to examine the fitness of specific mutations associated with the emergence of the parvoviruses. The first part of this study will involve the comparative analysis of complete genome sequence data. We will then determine the fitness of intermediate viruses at two stages of parvovirus emergence; first between the feline and initial canine virus, and second the adaptive improvement of canine viruses within dogs, which also resulted in a renewed ability to infect feline cells. These intermediate viruses provide unique information on the evolutionary trade-offs that may be implicit in the process of cross-species transmission. These viruses will be tested for their viability, and other biological properties, in tissue culture. In a small number of cases, the viruses will also be tested for their ability to replicate in animals. As a second major aim we will examine the intra-host genetic diversity of viral sequences when the viruses are replicating in either their donor and recipient host, such as feline parvovirus in dogs (leading to a restricted thymic infection), or H3N8 equine influenza virus in dogs. We will examine the extent and structure of sequence diversity found after growth of the virus in the different hosts, and use comparative sequence analysis determine whether the changes seen were subject to positive or negative selection pressure, or simply reflect the intrinsic mutational spectrum. Crucially, we will also analyze the extent and structure of diversity after viruses are allowed to undergo a single round of host-host transmission, which may impose additional and/or different selection pressures. As a comparison we will also conduct selection studies using cell culture, where we will measure the rate of emergence of antibody escape mutants for both the parvoviruses and influenza viruses, as well as receptor-selected mutants of the parvoviruses