Perpetuation of Francisella tularensis

描述(申请人提供)：图拉氏方济氏菌是图拉热症的病原体，图拉热症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在自然界中是通过扁虱、啮齿动物或兔子的循环来维持的，但它的巨大传染性和假定的环境稳定性表明它还有其他永久存在的模式。我们的长期目标是确定图拉热症暴发风险的近期决定因素，特别是在家禽流行性疾病之间如何维持该病原体。具体的假设是，在一个地方性疫源地内，遗传变异的集合种群结构促进了多种传播方式；某些变异可能更适合扁虱，而不是环境宿主。我们的假设基于我们对玛莎葡萄园岛持续爆发的肺炎性图拉热病疫情的调查，其中我们发现(1)11种图拉氏菌变种在我们的岛屿研究地点流行；(2)这些变种中的某些似乎仅与扁虱或动物有关。基于这些观察，我们现在寻求从实验上确定某些变异更有可能被扁虱遗传，在环境中保持稳定，还是导致肺部病理。因此，具体的目标是：1.确定变异体通过扁虱传播的能力是否不同，包括通过遗传维持的能力。我们将从多基因座可变数目串联重复序列分析(MLVA)定义的基因型中克隆菌株，并测量不同扁虱对这些克隆的媒介能力。2.确定变异体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对自由生活或寄生包囊形成原生动物的定殖性。我们将在体外测试每个基因在模拟环境压力下的生存能力和存活率。3.确定变异体对啮齿动物的传染性和毒性是否不同，包括诱发肺部病变或通过血液传播的能力。大鼠和小鼠将通过气管内滴注和肠外给药感染，并对组织进行组织病理学、免疫组化、聚合酶链式反应、培养和细胞因子mRNA表达的检查。综上所述，这些观察结果将为理解图拉热症的病原体如何在玛莎葡萄园岛持续存在，以及为什么肺炎性人类疾病在那里盛行提供了基础。

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.