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

描述(申请人提供)：感染蚊媒登革热病毒(DENV-1-4)的四种血清型是上升的原因之一；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50年中，严重登革热疾病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的风险显著增加，在一定程度上，DHF/DSS的增加可归因于特定地区多种血清型的共同循环增加。然而，每种DENV血清型都包含多种不同的基因类型，它们的核苷酸同源性相差6%，而基因类型又包括多个遗传上不同的谱系，这些谱系被称为毒株、分支或群。DENV流行病学的一个日益常见的特征是，某一特定血清型的某一基因或毒株入侵某一地区，并取代该同一血清型的本地基因或毒株。由于在异型继发感染或初次感染期间，基因类型和菌株在引起DHF/DSS的倾向上可能存在显著差异，世系更替事件可能对受影响地区的疾病动态产生重大影响。很明显，DENV中很高比例的谱系移位是由不同谱系对蚊子的内在感染性差异所介导的，但一些谱系获得更大蚊子感染性的机制尚未确定。我们之前已经研究了与斯里兰卡连续血统转移相关的三种DENV-3毒株的传染性。1989年，登革出血热后的DENV-3株取代了出血热前的株，导致出血热病例激增。2000年，超DHF株取代了后DHF株，DHF发病率再次上升。我们已经证明，对Ae来说，DHF后的菌株比DHF前的菌株更具传染性。埃及伊蚊，但令人惊讶的是，超DHF菌株对Ae的传染性较低。埃及伊蚊比DHF后的菌株。基于对具有或缺乏功能性rna干扰(RNAi)反应的蚊子培养细胞的初步研究，这项拟议的研究将检验这样一个假设，即病毒株与rNAi相互作用的差异可以解释后dhf株相对于dhf前株的更大传染性，但不能解释后dhf株更大的传染性。 相对于超DHF菌株的菌株。我们还将通过转录组分析，为后DHF和超DHF菌株之间的差异机制寻找新的假说。在缺乏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控制特别危险的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.