The Ecology and Classification of Rickettsia Species Phylotype G022, an Uncharacterized Bacterium from Ixodes pacificus Ticks

项目摘要/摘要 虽然壁虱和壁虱传播的病原体已经迅速成为对人类和 兽医公共卫生，越来越多的证据表明，许多由立克次体感染引起的硬蜱传播疾病可能是 由于其在人类和家畜中的不典型症状，在北美被低估了报告。硬壳纲 太平洋乳杆菌是美国太平洋西海岸病原菌和内共生菌的主要传播媒介。 与在加利福尼亚州其他物种中发现的致病性立克次体相比，致病性立克次体的生态学和生物学 太平洋立克次体在很大程度上仍未被发现。我们实验室发现了一个新的立克次体物种--立克次体 2011年、2013年和2020年，在加利福尼亚州北部的三个县寻找太平洋硬蜱成虫时，发现了G022系统型。 由于G022‘S的系统发育型，太平洋对虾在成体中的患病率很低(2-4.5%)，并发表了系统发育树，将 在其他致病性斑点热群里氏杆菌中，我们的假设是G022是一种病原性 立克次体。这项拟议的研究最终是我们先前关于生态和 太平洋立克次体致病机理的研究。我们的研究追求以下具体目标：1)我们将进行 通过收集G022型立克次体在太平洋伊蚊若虫体内的流行情况的调查 现场采集若虫及荧光定量PCR检测细菌；2)研究立克次体传播途径 以新西兰大白兔为食收集不同生长期硬蜱的G022种系 3)进行立克次体的繁殖和分离 利用扁虱胚胎细胞系和有限稀释试验分离到G022血型；4)我们将 立克次体系统型G022分离株的多位点序列分型 调查北加州家犬中是否存在立克次体种型G022感染。这 研究不仅将导致通过对纯细菌分离物的分型来正式命名G022系统型，而且还将使我们能够 开始收集关于细菌传播动态以及其潜在致病性的数据，长期 我们实验室的研究目标，对北加州的人类和动物宿主。

Project Summary/Abstract While both ticks and tick-borne disease agents have rapidly become a serious and growing threat to human and veterinary public health, mounting evidence indicates that many tick-borne diseases due to rickettsial infection may be under-reported in Northern America because of their uncharacteristic symptoms in humans and domestic animals. Ixodes pacificus is a principal vector for pathogenic and endosymbiotic bacteria on the Pacific West Coast of the United States. Compared to pathogenic rickettsiae identified in other tick species in California, the ecology and biology of pathogenic rickettsiae in I. pacificus remains largely unexplored. Our lab detected a novel Rickettsia species, Rickettsia species phylotype G022, in questing adult ticks of I. pacificus in three counties of Northern California in 2011, 2013, and 2020. Due to phylotype G022’s low prevalence (2-4.5%) in adult I. pacificus and published phylogenetic trees placing the bacterium within other pathogenic spotted fever group rickettsiae, our hypothesis is that phylotype G022 is a pathogenic Rickettsia. The proposed study ultimately serves as a continuation of our previous findings regarding the ecology and pathogenesis of Rickettsia species in I. pacificus. Our research pursues the following specific aims: 1) We will conduct a survey to estimate the prevalence of Rickettsia species phylotype G022 in nymphal ticks of I. pacificus by collecting the nymphs from the field and detecting the bacterium by real-time PCR; 2) We will study transmission routes of Rickettsia species phylotype G022 in I. pacificus by collecting all life stages of the ticks via feeding on New Zealand white rabbits and detecting the bacterium by real-time PCR; 3) We will perform the propagation and isolation of the Rickettsia phylotype G022 isolate from I. pacificus using tick embryonic cell lines and limiting dilution assay; 4) We will perform the molecular typing of the Rickettsia species phylotype G022 isolate by Multilocus Sequence Typing; 5) We will investigate the presence of Rickettsia species phylotype G022 infection in domestic dogs from Northern California. This study will not only result in the official naming of phylotype G022 by typing the pure bacterial isolate, but also enable us to start gathering data on transmission dynamics of the bacterium as well as its potential pathogenicity, the long-term research goal of our lab, to humans and animal hosts in Northern California.