St Helena Hospital Clearlake, Clearlake, California, USA.
Clin Infect Dis. 2010 Feb 15;50(4):541-8. doi: 10.1086/649926.
Four spotted fever group rickettsiae (SFGR) are known to infect humans in the United States. A member of the SFGR designated 364D and detected in Dermacentor occidentalis ticks has not previously been identified as a human pathogen.
An 80-year-old man from a rural northern California community presented with an eschar on his forearm. A skin punch biopsy of the lesion was evaluated by immunohistochemistry and molecular analysis. Serum specimens obtained from the patient and 3 other area residents with similar illnesses were tested by immunofluorescence and Western immunoblot for antibodies to SFGR. Ticks were collected near the patient's residence and tested for SFGR.
Abundant intracellular rickettsiae and fragmented rickettsial antigens were observed in the mononuclear inflammatory infiltrates of the biopsy. Nucleotide sequences of DNA fragments amplified from the biopsy were identical to those of 364D. Convalescent sera from all four patients exhibited high immunoglobulin G titers to Rickettsia rickettsii, Rickettsia rhipicephali, and 364D antigens. Three adult D. occidentalis were positive for 364D, R. rhipicephali, and an unidentified Rickettsia species.
This is the first confirmation of human disease associated with the SFGR 364D, which was likely transmitted by D. occidentalis. Although the patients described here presented with a single cutaneous eschar as the principal manifestation, the full spectrum of illness associated with 364D has yet to be determined. Possible infection with 364D or other SFGR should be confirmed through molecular techniques in patients who present with "spotless" Rocky Mountain spotted fever or have serum antibodies to R. rickettsii with group-specific assays.
已知斑点热群立克次体（SFGR）会感染美国的人类。一种被指定为 364D 的 SFGR 并在西方花蜱中检测到，以前并未被确定为人类病原体。
一位来自加利福尼亚州北部农村社区的 80 岁男性出现前臂疖。对病变进行皮肤打孔活检，通过免疫组织化学和分子分析进行评估。从患者和其他 3 位具有类似疾病的当地居民获得血清标本，通过免疫荧光和 Western 免疫印迹检测 SFGR 抗体。在患者住所附近采集蜱并检测 SFGR。
活检单核炎性浸润中观察到丰富的细胞内立克次体和碎裂的立克次体抗原。从活检中扩增的 DNA 片段的核苷酸序列与 364D 相同。所有 4 位患者的恢复期血清均对 Rickettsia rickettsii、Rickettsia rhipicephali 和 364D 抗原表现出高免疫球蛋白 G 滴度。3 只成年西方花蜱对 364D、R. rhipicephali 和一种未鉴定的立克次体物种呈阳性。
这是首次确认与 SFGR 364D 相关的人类疾病，该疾病可能由西方花蜱传播。尽管这里描述的患者主要表现为单个皮肤疖，但与 364D 相关的完整疾病谱尚未确定。在出现“无斑”落基山斑点热或具有群体特异性检测的针对 R. rickettsii 的血清抗体的患者中，应通过分子技术确认可能感染 364D 或其他 SFGR。
