许多感染人与动物的病原体均来自于节肢动物。蜱可以携带大量的病毒与细菌(包括立克次氏体目细菌)，是人与动物多种病原体的重要传播媒介与宿主。立克次氏体目细菌属于α变形菌门，是一类严格的胞内寄生微生物，其传播媒介主要为蜱。立克次氏体目中的多种细菌是人与动物疾病的病原体，可引起严重的疾病，甚至造成死亡。蜱传立克次氏体目细菌引起的疾病属于自然疫源性疾病，因此，查清楚其在自然疫源地中的流行情况对于疾病的防控非常重要。本项目拟对陕西省的蜱及其携带的立克次氏体目细菌进行调查。采用分子生物学方法，研究立克次氏体目细菌在蜱与家养动物中的流行状况，揭示其遗传特征及多样性、地理分布、以及与宿主间的关系。发现新立克次氏体目细菌，并用细胞培养的方法分离。采用最大似然法与贝叶斯系统发生分析方法研究该地区立克次氏体目细菌与国内外已知病原体间的进化关系。本项目将为陕西省立克次体病的预防与控制提供科学依据。

Arthropod has been an important source of pathogens infecting humans and animals. Ticks can harbor a large number of viruses and bacteria (including Rickettsiales) and act as the vectors and hosts of humans and animals etiologic agents. Rickettsiales belong to the alpha Proteobacteria and comprises of a group of obligate intracellular bacterium. Most of them are transmitted by ticks through blood-feeding. Many Rickeckttsiales bacterium are best known as agents of human beings and veterinary disease, causing severe diseases including death. Diseases caused by tick-borne Rickettsiales are natural-focal diseases, therefore, investigating the epidemic situation of Rickettsiales bacterium in the natural foci is important for disease prevention and control. Our project aims to perform the molecular epidemiological investigation of Rickettsiales ticks in Shaanxi Province. Here, using the molecular biological methods, the infection of Rickettsiales bacterium in ticks and domestic animals will be inferred. In addition, this study will also demonstrate the genetic characters, diversity and geographic distribution of Rickettsiales, and their association with hosts. Besides, identification and isolation of novel Rickettsiales will also be performed. The phylogenetic relationship between strains in this study and other known strains in and outside China will be estimated by using Maximum likelihood and Bayesian methods. The data from this project will be helpful to prevent the disease caused by Rickettsiales in Shaanxi Province.