Apperson Charles S, Engber Barry, Nicholson William L, Mead Daniel G, Engel Jeffrey, Yabsley Michael J, Dail Kathy, Johnson Joey, Watson D Wesley
Department of Entomology, North Carolina State University, Raleigh, North Carolina 27695-7647, USA.
Vector Borne Zoonotic Dis. 2008 Oct;8(5):597-606. doi: 10.1089/vbz.2007.0271.
Cases of Rocky Mountain spotted fever (RMSF) in North Carolina have escalated markedly since 2000. In 2005, we identified a county in the Piedmont region with high case numbers of RMSF. We collected ticks and examined them for bacterial pathogens using molecular methods to determine if a novel tick vector or spotted fever group rickettsiae (SFGR) might be emerging. Amblyomma americanum, the lone star tick, comprised 99.6% of 6,502 specimens collected in suburban landscapes. In contrast, Dermacentor variabilis, the American dog tick, a principal vector of Rickettsia rickettsii, comprised < 1% of the ticks collected. Eleven of 25 lone star tick pools tested were infected with "Rickettsia amblyommii," an informally named SFGR. Sera from patients from the same county who were presumptively diagnosed by local physicians with a tick-borne illness were tested by an indirect immunofluorescence antibody (IFA) assay to confirm clinical diagnoses. Three of six patients classified as probable RMSF cases demonstrated a fourfold or greater rise in IgG class antibody titers between paired acute and convalescent sera to "R. amblyommii" antigens, but not to R. rickettsii antigens. White-tailed deer, Odocoileus virginianus, are preferred hosts of lone star ticks. Blood samples collected from hunter-killed deer from the same county were tested by IFA test for antibodies to Ehrlichia chaffeensis and "R. amblyommii." Twenty-eight (87%) of 32 deer were positive for antibodies to E. chaffeensis, but only 1 (3%) of the deer exhibited antibodies to "R. amblyommii," suggesting that deer are not the source of "R. amblyommii" infection for lone star ticks. We propose that some cases of rickettsiosis reported as RMSF may have been caused by "R. amblyommii" transmitted through the bite of A. americanum.
自2000年以来，北卡罗来纳州落基山斑疹热（RMSF）病例显著增加。2005年，我们在皮埃蒙特地区确定了一个落基山斑疹热病例数较高的县。我们采集了蜱虫，并使用分子方法检测其中的细菌病原体，以确定是否可能出现了新的蜱虫传播媒介或斑点热群立克次体（SFGR）。美洲钝眼蜱，即孤星蜱，在郊区采集的6502个样本中占99.6%。相比之下，变异革蜱，即美国犬蜱，作为立氏立克次体的主要传播媒介，在所采集的蜱虫中占比不到1%。在检测的25个孤星蜱样本池中，有11个感染了“安氏立克次体”，这是一种非正式命名的斑点热群立克次体。对来自同一县、被当地医生初步诊断为蜱传疾病的患者血清，通过间接免疫荧光抗体（IFA）检测来确诊临床诊断。在被归类为可能的落基山斑疹热病例的6名患者中，有3名患者急性期和恢复期配对血清中针对“安氏立克次体”抗原的IgG类抗体滴度升高了四倍或更多，但针对立氏立克次体抗原的抗体滴度未升高。白尾鹿，即弗吉尼亚鹿，是孤星蜱的首选宿主。对从同一县猎人捕杀的鹿采集的血样进行IFA检测，以检测针对恰菲埃立克体和“安氏立克次体”的抗体。32只鹿中有28只（87%）针对恰菲埃立克体抗体呈阳性，但只有1只（3%）鹿显示针对“安氏立克次体”的抗体，这表明鹿不是孤星蜱感染“安氏立克次体”的来源。我们认为，一些被报告为落基山斑疹热的立克次体病病例可能是由通过美洲钝眼蜱叮咬传播的“安氏立克次体”引起的。
