Stromdahl Ellen Y, Vince Mary A, Billingsley Peggy M, Dobbs Nicole A, Williamson Phillip C
Entomological Sciences Program, US Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD 21010-5403, USA.
Vector Borne Zoonotic Dis. 2008 Spring;8(1):15-24. doi: 10.1089/vbz.2007.0138.
Polymerase chain reaction analysis of Amblyomma americanum adults, nymphs, and larvae from Aberdeen Proving Ground, MD (APG), revealed a very high prevalence of a spotted fever group (SFG) rickettsia. Restriction fragment length polymorphism (RFLP) and sequence analysis identified "Rickettsia amblyommii." This organism is not yet described or well studied, and its pathogenicity is unknown; however, investigations of the organism are warranted because of its high prevalence in A. americanum. This tick is extremely abundant at military training facilities in the south, central, and Mid-Atlantic United States, and many soldiers experience multiple concurrent tick bites. Bites by R. amblyommii-infected A. americanum may account for rates of SFG rickettsia seropositivity that are higher than reported rates of Rocky Mountain spotted fever (RMSF) cases from the same location. Seroconversion to SFG rickettsia following bites of A. americanum may suggest that R. amblyommii is infectious in humans. Subclinical infection in the numerous A. americanum tick bite victims could contaminate donated blood and compromise immunodeficient recipients. Detection of R. amblyommii in questing A. americanum larvae suggests transovarial transmission. The absence of R. rickettsii, the agent of RMSF, in A. americanum may be due to transovarial interference by R. amblyommii. The likelihood of pathogen transmission by larvae is magnified by their habit of mass attack. The very small size of the larvae is also a risk factor for pathogen transmission. High R. amblyommii prevalence in populations of A. americanum presage co-infection with other A. americanum-borne pathogens. A. americanum nymphs and adults from APG were found to be co-infected with R. amblyommii and Borrelia lonestari, Ehrlichia chaffeensis and Ehrlichia ewingii, respectively, and larval pools were infected with both R. amblyommii and B. lonestari. Co-infections can compound effects and complicate diagnosis of tick-borne disease.
对来自马里兰州阿伯丁试验场（APG）的美洲钝眼蜱成虫、若虫和幼虫进行聚合酶链反应分析，结果显示斑点热群（SFG）立克次体的感染率非常高。限制性片段长度多态性（RFLP）和序列分析鉴定出了“美洲钝眼蜱立克次体”。这种微生物尚未被描述或深入研究，其致病性也未知；然而，鉴于其在美洲钝眼蜱中高感染率，有必要对该微生物展开调查。这种蜱在美国南部、中部和大西洋中部的军事训练设施中极其常见，许多士兵会同时遭受多次蜱叮咬。被感染美洲钝眼蜱立克次体的美洲钝眼蜱叮咬，可能是导致同一地点SFG立克次体血清阳性率高于落基山斑疹热（RMSF）报告病例率的原因。被美洲钝眼蜱叮咬后出现SFG立克次体血清转化，可能表明美洲钝眼蜱立克次体可感染人类。众多被美洲钝眼蜱叮咬的受害者发生亚临床感染，可能会污染捐献的血液并危及免疫功能低下的受血者。在觅食的美洲钝眼蜱幼虫中检测到美洲钝眼蜱立克次体，提示存在经卵传播。美洲钝眼蜱中不存在RMSF病原体立氏立克次体，可能是由于美洲钝眼蜱立克次体的经卵干扰。幼虫成群攻击的习性增加了病原体传播的可能性。幼虫非常小也是病原体传播的一个危险因素。美洲钝眼蜱群体中美洲钝眼蜱立克次体的高感染率预示着会与其他由美洲钝眼蜱传播的病原体发生共同感染。研究发现，来自APG的美洲钝眼蜱若虫和成虫分别同时感染了美洲钝眼蜱立克次体和孤独疏螺旋体、查菲埃立克体和尤因埃立克体，幼虫群体同时感染了美洲钝眼蜱立克次体和孤独疏螺旋体。共同感染会使蜱传疾病的影响叠加并使诊断复杂化。
