Coinfection by Rickettsiae in Amblyomma maculatum: Impact on Disease Transmission

描述（由申请人提供）：近世纪前，落基山斑疹热在美国开始报告，目前病例处于最高水平。然而，在美国，除了立克次体以外的立克次体也能引起斑点热，这一点并没有得到广泛的认识。虽然在过去的二十年中已经确定了其他斑点热群立克次体（SFGR），但现有的“斑点热立克次体病”流行病学知识仍然存在差距，CDC现在使用的命名法代替落基山斑点热。由斑点钝眼蜱传播的帕克氏立克次体最近成为斑点热立克次体病的一个致病因素。然而，“安氏立克次体”，一个新的SFGR也存在于A。斑，是知之甚少，其疾病的影响未知。同域分布的立克次体在同一蜱种内的相互作用如何影响立克次体的传播和维持，在A。maculatum-SFGR系统事实上，这种蜱立克次体系统可能不同于先前描述的革蜱和SFGR。本研究的长期目标是了解蜱中SFGR的生物学和关系，使用A。maculatum-SFGR系统作为模型，以便更准确地描绘斑点热立克次体病的复杂流行病学。为了实现这一目标，R15 AREA应用程序的总体目标是评估R的潜在贡献。parkeri和"Ca. R. andendelysis "in A.斑点热立克次体病之间的相互作用。在脊椎动物上的蜱虫进食期间的斑点。核心假设是“Ca。R. andesterone "不会传染，但会影响R. parkeri。本研究的基本原理是，了解SFGR而不是R。立克次体有助于疾病的传播和立克次体的维持，有助于阐明斑点热立克次体病的流行病学。助理maculatum-SFGR系统是评价蜱-立克次体相互作用的理想模型。为了与区域目标保持一致，学生将参加拟议的 在不接触高致病性物种的情况下研究新出现的病媒生物。在这个修订的R15申请中，提出了两个目的来实现目标：（1）评估"Ca. R. andestruca "和R. parkeri在单独和合并感染A. maculatum，和"Ca. R.和"deletion"对R. parkeri;和（2）评估共喂养和"Ca. R.和"degenerative"的存在，使蜱收购R。parkeri。这项研究意义重大，因为它促进了对潜在的新型蜱-立克次体相互作用的进一步了解。这些知识将有助于准确评估斑点热立克次体病流行病学数据。最终，对这些数据的合理解释将有助于公共卫生政策的制定。最后，拟议的研究是创新的，因为初步数据挑战了跨卵干扰发生在所有蜱传SFGR的假设，这表明在某些系统中可能会流行合并感染。因此，节肢动物中的微生物相互作用可能比目前认为的更复杂。

DESCRIPTION (provided by applicant): Rocky Mountain spotted fever became reportable in the United States nearly a century ago and cases are currently at their highest levels. However, it is not widely recognized that rickettsiae other than Rickettsia rickettsii can cause spotted fevr in the United States. Although other spotted fever group rickettsiae (SFGR) have been identified over the last two decades, there remains a gap in existing knowledge of the epidemiology of "spotted fever rickettsiosis," nomenclature CDC now uses in place of Rocky Mountain spotted fever. Rickettsia parkeri, which is transmitted by Amblyomma maculatum, recently emerged as a contributor to spotted fever rickettsiosis. However, "Candidatus Rickettsia andeanae," a novel SFGR also present in A. maculatum, is poorly understood and its disease implications unknown. How interactions between sympatric rickettsiae within the same tick species may affect rickettsial transmission and maintenance, has not been explored in the A. maculatum-SFGR system. In fact, this tick-rickettsial system may differ from those previously described for Dermacentor ticks and SFGR. The long-term goal of this research is to understand the biology and relationships between SFGR in ticks, using the A. maculatum-SFGR system as a model, in order to more accurately portray the complex epidemiology of spotted fever rickettsiosis. To move toward this goal, the overall objective of this R15 AREA application is to evaluate the potential contribution of R. parkeri and "Ca. R. andeanae" in A. maculatum to spotted fever rickettsiosis by understanding interactions between these SFGR in A. maculatum during tick feeding on vertebrates. The central hypothesis is that "Ca. R. andeanae" will not be infectious but will affect transmission and maintenance of R. parkeri. The rationale for the proposed research is that understanding how SFGR other than R. rickettsii contribute to disease, and to transmission and maintenance of rickettsiae, will help clarify spotted fever rickettsiosis epidemiology. The A. maculatum-SFGR system provides an ideal model with which to evaluate tick-rickettsia interactions. In keeping with AREA goals, students will participate in the proposed research on emerging vector-borne organisms without being exposed to highly pathogenic species. In this revised R15 application, two Aims are proposed to accomplish the goals: (1) to evaluate tissue tropism of "Ca. R. andeanae" and R. parkeri in singly and co-infected A. maculatum, and effect(s) of "Ca. R. andeanae" on transmission of R. parkeri; and (2) to evaluate co-feeding and "Ca. R. andeanae" presence in enabling tick acquisition of R. parkeri. The proposed research is significant because it promotes further understanding of potentially novel tick-rickettsia interactions. This knowledge will assist in accurately evaluating spotted fever rickettsiosis epidemiologic data. Ultimately, rational interpretation of these data will be useful in public health policy making. Finally, the proposed research is innovative because preliminary data challenge the presumption that transovarial interference occurs in all tick-borne SFGR, suggesting that co-infections may prevail in some systems. Thus, microbial interactions in arthropods may be more complex than is currently believed.