Perpetuation of Francisella tularensis

描述（由申请人提供）：土拉菌弗朗西斯菌是土拉菌病的病原体，土拉菌病是一种急性发热性感染，具有不同的表现和结果。虽然据说这种病原体是通过蜱虫、啮齿动物或兔子的循环在自然界中维持的，但其强大的传染性和假定的环境稳定性表明了其他的延续模式。我们的长期目标是确定土拉菌病暴发风险的近端决定因素，特别是在动物流行病之间如何维持病原体。具体的假设是，在一个地方性疫源地内，遗传变异的超种群结构促进了多种传播模式；与环境宿主相比，某些变异可能更适合蜱虫。我们的假设基于我们对玛莎葡萄园岛正在进行的肺炎土拉菌病暴发的调查，其中我们发现(1)11种土拉菌变体在我们的岛屿研究地点传播；(2)这些变异中的某些似乎只与蜱虫或动物有关。基于这些观察结果，我们现在试图通过实验确定某些变异是否更有可能被蜱虫遗传，在环境中保持稳定，或引起肺部病理。因此，具体目标是：1。确定变种通过蜱传播的能力是否不同，包括通过遗传维持。我们将从多位点可变数串联重复分析（MLVA）定义的基因型中克隆菌株，并测量这些克隆中各种蜱的媒介能力。2. 确定变异在环境中稳定存在的能力是否不同，包括对干燥的抵抗力，在水中的生存能力，以及自由生物或寄生囊肿形成的原生动物的定植能力。我们将在体外模拟环境胁迫下测量每个基因型的生存能力和存活率。3. 确定变异对啮齿动物的传染性和毒力是否不同，包括诱导肺部病理或血源性传播的能力。大鼠和小鼠将通过气管内滴注和肠外给药感染，并通过组织病理学、免疫组织化学、PCR、培养和细胞因子mRNA表达检查组织。综上所述，这些观察结果将为理解土拉菌病是如何在玛莎葡萄园岛持续存在的，以及为什么人类肺炎疾病在那里流行提供基础。

DESCRIPTION (provided by applicant): Francisella tularensis is the causative agent of tularemia, an acute febrile infection with variable presentation and outcomes. Although the agent is said to be maintained in nature by cycles involving ticks and rodents or rabbits, its great infectivity and presumptive environmental stability suggests other modes of perpetuation. Our longterm goal is to determine the proximal determinants of risk for outbreaks of tularemia, and in particular, how the agent is maintained between epizootics. The specific hypothesis is that multiple modes of transmission are facilitated by a metapopulation structure of genetic variants within an enzootic focus; certain variants may be better adapted to ticks as opposed to environmental reservoirs. We base our hypothesis on our investigation of the ongoing pneumonic tularemia outbreak on Martha's Vineyard, wherein we have found (1) that 11 F. tularensis variants circulate in our island study sites; and (2) that certain of these variants appear to be associated solely with ticks or with animals. Based on these observations, we now seek to determine experimentally whether certain variants are more likely to be inherited by ticks, remain stable within the environment, or cause pulmonary pathology. The specific aims, therefore, are to: 1. Determine whether variants differ in their capacity to be transmitted by ticks, including maintenance by inheritance. We will clone strains from the multiple loci variable number tandem repeat analysis (MLVA)-defined genotypes, and measure the vector competence of various ticks for such clones. 2. Determine whether variants differ in their capacity to stably persist in the environment, including resistance to dessication, survival in water, and colonisation of freeliving or parasitic cyst-forming protozoa. We will measure the viability and survival of each genotype under simulated environmental stresses in vitro. 3. Determine whether variants differ in their infectivity to and virulence within rodents, including capacity to induce pulmonary pathology or hematogenously disseminate. Rats and mice will be infected by intratracheal instillation, as well as parenteral delivery, and tissues examined by histopathology, immunohistochemistry, PCR, cultivation, and cytokine mRNA expression. Taken together, these observations will provide a basis for understanding how the agent of tularemia is perpetuated on Martha's Vineyard, and why pneumonic human disease is prevalent there.