INTERSPECIFIC COMPETITION BETWEEN RICKETTSIAE IN TICKS

描述（由申请人提供）：我们的初步研究和其他研究清楚地表明，一种斑点热组立克次体在蜱虫媒介、变种革螨和安德氏弓形虫中占主导地位。在蒙大拿州、俄亥俄州、加利福尼亚州和马里兰州进行的广泛蜱虫调查显示，非致病性立克次体在蜱虫种群中占主导地位。非致病性蜱虫共生体的存在可能解释了立克次体在安德氏弓形虫和变异弓形虫中的低感染率，从而导致美国落基山斑疹热的人类病例呈斑块状分布。本项目旨在探讨蜱类多重立克次体感染的分子后果和流行病学意义。我们提出蜱个体内专性细胞内立克次体之间的相互作用可能具有足够的相关性和强度来改变蜱的媒介能力。因此，我们重点研究了变异性蜱经口获得的立克次体共生体，即山地立克次体和孔雀立克次体。本文研究了山田鼠经生殖道干扰变异蜱的流行率和相对效率。我们还关注了蜱卵巢组织中响应立克次体感染的差异表达的变异性迪克氏菌基因。我们从感染和未感染的变异弧菌中构建了几个组织特异性cDNA文库。为了更新应用，我们建议进一步完善和表征跨卵巢干扰的分子机制。在第一个目标下的研究确定了确定的分子的功能作用，这些分子开始排除蜱卵巢的继发性立克次体感染。第二个目标将集中在调查选定的蜱分子在立克次体的维持和传播中的作用。

DESCRIPTION (provided by applicant): Our preliminary studies and those of others clearly demonstrate a dominance of a single species of spotted fever group rickettsiae in ixodid tick vectors, Dermacentor variabilis and D. andersoni. Extensive tick surveys in Montana, Ohio, California, and Maryland revealed the dominance of nonpathogenic rickettsiae in tick populations. The presence of nonpathogenic tick symbionts may account for the low infection rates of Rickettsia rickettsii in D. andersoni and D. variabilis thus resulting in patchy distribution of human cases of Rocky Mountain spotted fever in the US. This project was initiated to investigate the molecular consequences and epidemiological significance of multiple rickettsial infections in ticks. We have proposed that the interactive effects between obligate intracellular rickettsiae within individual ticks may be of sufficient relevance and magnitude to alter the vector competence of ticks. Thus, we have focused on rickettsial symbionts acquired transovarially by D. variabilis ticks, namely Rickettsia montanensis and R. peacockii. We have investigated the prevalence and relative efficiency of transovarial interference of R. montanensis within D. variabilis ticks as mediated by R. rhipicephali. We have also focused on the D. variabilis genes that are differentially expressed in response to rickettsial infection within tick ovarian tissues. We have constructed several tissue-specific cDNA libraries from infected and uninfected D. variabilis. For the renewal application, we are proposing to further refine and characterize molecular mechanisms underlying transovarial interference. Studies under first aim define the functional role of identified molecules that initiate the exclusion of secondary rickettsial infections of tick ovaries. The second aim will be focused on investigating the role of the selected tick molecules in the maintenance and transmission of rickettsiae.