Coinfection by Rickettsiae in Amblyomma maculatum: Impact on Disease Transmission

描述（由申请人提供）：落基山斑疹热在近一个世纪前在美国开始报告，目前病例处于最高水平。然而，在美国，人们还没有广泛认识到除了立克次体以外的立克次体也能引起斑疹热。虽然在过去的二十年中已经发现了其他斑点热组立克次体（SFGR），但对“斑点热立克次体病”的现有流行病学知识仍然存在差距，CDC现在使用命名法代替落基山斑疹热。由斑状无眼肿传播的白氏立克次体，最近作为斑点热立克次体病的一种贡献者出现。然而，“候选立克次体”，一种新的SFGR也存在于a . maculatum中，人们对其了解甚少，其疾病含义尚不清楚。同一蜱种内同域立克次体之间的相互作用如何影响立克次体的传播和维持，尚未在斑点蜱- sfgr系统中进行探讨。事实上，这种蜱-立克次体系统可能不同于先前描述的革螨蜱和SFGR。本研究的长期目标是了解蜱虫SFGR的生物学和相互关系，以斑点a . maculata -SFGR系统为模型，以便更准确地描述斑点热立克次体病的复杂流行病学。为了实现这一目标，本R15区域应用的总体目标是通过了解蜱虫捕食脊椎动物过程中斑斑拟虫SFGR之间的相互作用，评估斑斑拟虫中的parkeri和Ca. R. andeanae对斑点热立克次病的潜在贡献。中心假设是，“andeanae Ca. R. andeanae”不会具有传染性，但会影响parkeri的传播和维持。提出这项研究的基本原理是，了解除了立克次体之外的SFGR是如何导致立克次体的疾病以及传播和维持立克次体的，将有助于澄清斑点热立克次体病的流行病学。该系统为蜱-立克次体相互作用的评价提供了一个理想的模型。为了与区域目标保持一致，学生将参与拟议的

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.