Mechanisms of competitive displacement by lineages of mosquito-borne dengue virus

描述（由申请人提供）：蚊媒登革热病毒（DENV-1-4）的四种血清型的感染正在上升;目前估计，在大约100个国家中，每年有近4亿人感染DENV。登革热的表现形式从亚临床感染到经典登革热再到严重疾病，包括登革出血热（DHF）和登革休克综合征（DSS）。在过去五十年中，严重登革热的范围和发病率急剧上升。在异型（第二血清型）继发感染期间，DHF/DSS的风险显著升高，DHF/DSS的这种增加部分归因于给定地区多种血清型的共循环增加。然而，每种DENV血清型涵盖多个基因型，其相差> 6%核苷酸同一性，并且基因型进而包含多个遗传上不同的谱系，其被称为株、进化枝或群。DENV流行病学的一个越来越常见的特征是给定血清型的基因型或毒株侵入区域，并置换相同血清型的天然基因型或毒株。由于基因型和菌株在异型继发感染或原发感染期间引起DHF/DSS的倾向可能显著不同，因此谱系替代事件可能对受影响区域的疾病动态产生重大影响。很明显，DENV中高比例的谱系置换是由蚊子内在感染性的谱系之间的差异介导的，但是一些谱系实现更大的蚊子感染性的机制尚未确定。我们先前研究了与斯里兰卡连续谱系置换相关的三种DENV-3菌株的感染性。1989年，登革出血热后的DENV-3毒株取代了登革出血热前的毒株，导致登革出血热病例激增。2000年，超DHF菌株取代后DHF菌株，DHF发病率再次上升。我们已经证明，后DHF菌株比前DHF菌株对Ae更具感染性。但令人惊讶的是，ultra-DHF菌株对Ae.与DHF后菌株相比。基于对培养的蚊子细胞进行的初步研究，这些蚊子细胞具有或缺乏功能性RNA干扰（RNAi）反应，拟议的研究将测试以下假设，即病毒株与RNAi相互作用的差异导致DHF后毒株相对于DHF前毒株的感染性更强，但不是DHF后毒株的感染性更强。 应变相对于ultra-DHF应变。我们还将寻求，通过转录组分析，新的假说的机制之间的差异，DHF后和ultra-DHF株。在没有登革热疫苗或抗病毒药物的情况下，了解DENV谱系置换的进化驱动因素至关重要，以便最终能够识别并可能遏制特别危险的DENV毒株的传播。

DESCRIPTION (provided by applicant): Infections with the four serotypes of mosquito-borne dengue virus (DENV-1-4) are one the rise; it is currently estimated that almost 400 million people are infected with DENV annually in approximately 100 countries. Dengue disease ranges in manifestation from subclinical infection to classical dengue fever to severe disease, including dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). The range and incidence of severe dengue disease have risen dramatically in the last five decades. Risk of DHF/DSS is significantly elevated during a heterotypic (second serotype) secondary infection, and in part this increase in DHF/DSS is attributable in increasing co-circulation of multiple serotypes in a given locality. However each DENV serotype encompasses multiple genotypes, which differ by > 6% nucleotide identity, and genotypes in turn comprise multiple, genetically-distinct lineages, which have been termed strains, clades or groups. An increasingly common feature of DENV epidemiology is the invasion of a region by a genotype or strain of a given serotype and displacement of the native genotype or strain of that same serotype. Because genotypes and strains may differ significantly in their tendency to cause DHF/DSS during a heterotypic secondary infection or during primary infection, lineage replacement events can have a substantial impact on disease dynamics in the affected region. It is clear that a high proportion of lineage displacements in DENV are mediated by differences between lineages in intrinsic infectivity for mosquitoes, but the mechanisms by which some lineages achieve greater mosquito infectivity have not been identified. We have previously studied the infectivity of three strains of DENV-3 associated with consecutive lineage displacements in Sri Lanka. In 1989, the post-DHF strain of DENV-3 displaced the pre-DHF strain, resulting in a surge of DHF cases. In 2000, the ultra-DHF strain displaced the post-DHF strain, and DHF incidence rose again. We have shown that the post-DHF strain is more infectious than the pre-DHF strain for Ae. aegypti, but, surprisingly, that the ultra-DHF strain is less infectious for Ae. aegypti than the post-DHF strain. Building on preliminary studies in cultured mosquito cells that either possess or lack a functional RNA interference (RNAi) response, the proposed research will test the hypothesis that differences in virus strain interactions with RNAi account for the greater infectivity of the post- DHF strain relative to the pre-DHF strain but not for the greater infectivity of the post-DHF strain relative to the ultra-DHF strain. We will also seek, via transcriptome analysis, novel hypotheses for the mechanisms underpinning differences between the post-DHF and ultra-DHF strains. In the absence of a dengue vaccine or antiviral drugs, it is critical to understand the evolutionary drivers of DENV lineage displacement in order, eventually, to be able to identify and perhaps contain the spread of particularly dangerous DENV strains.