Roth Tara, Lane Robert S, Foley Janet
Department of Medicine and Epidemiology, University of California, Davis, CA 95616 (
Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720 (
J Med Entomol. 2017 Mar 1;54(2):492-495. doi: 10.1093/jme/tjw202.
Francisella tularensis and Rickettsia spp. have been cultured from Haemaphysalis leporispalustris Packard, but their prevalence in this tick has not been determined using modern molecular methods. We collected H. leporispalustris by flagging vegetation and leaf litter and from lagomorphs (Lepus californicus Gray and Sylvilagus bachmani (Waterhouse)) in northern California. Francisella tularensis DNA was not detected in any of 1,030 ticks tested by polymerase chain reaction (PCR), whereas 0.4% of larvae tested in pools, 0 of 117 individual nymphs, and 2.3% of 164 adult ticks were PCR-positive for Rickettsia spp. Positive sites were Laurel Canyon Trail in Tilden Regional Park in Alameda Contra Costa County, with a Rickettsia spp. prevalence of 0.6% in 2009, and Hopland Research and Extension Center in Mendocino County, with a prevalence of 4.2% in 1988. DNA sequencing revealed R. felis, the agent of cat-flea typhus, in two larval pools from shaded California bay and live oak leaf litter in Contra Costa County and one adult tick from a L. californicus in chaparral in Mendocino County. The R. felis in unfed, questing larvae demonstrates that H. leporispalustris can transmit this rickettsia transovarially. Although R. felis is increasingly found in diverse arthropods and geographical regions, prior literature suggests a typical epidemiological cycle involving mesocarnivores and the cat flea, Ctenocephalides felis. To our knowledge, this is the first report of R. felis in H. leporispalustris. Natural infection and transovarial transmission of this pathogen in the tick indicate the existence of a previously undocumented wild-lands transmission cycle that may intersect mesocarnivore-reservoired cycles and collectively affect human health risk.
土拉弗朗西斯菌和立克次氏体属细菌已从北美野兔血蜱（Haemaphysalis leporispalustris Packard）中培养出来，但尚未使用现代分子方法确定它们在这种蜱中的流行率。我们通过在加利福尼亚州北部的植被和落叶层以及兔形目动物（加利福尼亚兔（Lepus californicus Gray）和巴氏林兔（Sylvilagus bachmani (Waterhouse)））身上悬挂捕捉来收集北美野兔血蜱。通过聚合酶链反应（PCR）检测的1030只蜱中均未检测到土拉弗朗西斯菌DNA，而在混合检测的幼虫中有0.4%呈阳性，117只若蜱均为阴性，164只成蜱中有2.3%的立克次氏体属细菌PCR检测呈阳性。阳性地点是阿拉米达-康特拉科斯塔县蒂尔登地区公园的劳雷尔峡谷步道，2009年立克次氏体属细菌的流行率为0.6%，以及门多西诺县的霍普兰德研究与推广中心，1988年的流行率为4.2%。DNA测序显示，在来自康特拉科斯塔县阴凉的加利福尼亚月桂树和活橡树叶层的两个幼虫混合样本以及来自门多西诺县丛林中一只加利福尼亚兔身上的一只成蜱中发现了猫蚤斑疹伤寒病原体猫立克次氏体（R. felis）。未进食、正在寻找宿主的幼虫身上的猫立克次氏体表明北美野兔血蜱可以经卵传播这种立克次氏体。尽管猫立克次氏体在不同的节肢动物和地理区域中越来越常见，但先前的文献表明其典型的流行病学循环涉及中型食肉动物和猫蚤（Ctenocephalides felis）。据我们所知，这是关于猫立克次氏体在北美野兔血蜱中的首次报道。这种病原体在蜱中的自然感染和经卵传播表明存在一个以前未记录的野生地区传播循环，该循环可能与中型食肉动物作为宿主的循环相交，并共同影响人类健康风险。
