Gaines David N, Operario Darwin J, Stroup Suzanne, Stromdahl Ellen, Wright Chelsea, Gaff Holly, Broyhill James, Smith Joshua, Norris Douglas E, Henning Tyler, Lucas Agape, Houpt Eric
1 Virginia Department of Health , Richmond, Virginia.
Vector Borne Zoonotic Dis. 2014 May;14(5):307-16. doi: 10.1089/vbz.2013.1509. Epub 2014 Apr 18.
The population of the lone star tick Amblyomma americanum has expanded in North America over the last several decades. It is known to be an aggressive and nondiscriminatory biter and is by far the most common human-biting tick encountered in Virginia. Few studies of human pathogen prevalence in ticks have been conducted in our state since the mid-twentieth century. We developed a six-plex real-time PCR assay to detect three Ehrlichia species (E. chaffeensis, E. ewingii, and Panola Mountain Ehrlichia) and three spotted fever group Rickettsiae (SFGR; R. amblyommii, R. parkeri, and R. rickettsii) and used it to test A. americanum from around the state. Our studies revealed a presence of all three Ehrlichia species (0-24.5%) and a high prevalence (50-80%) of R. amblyommii, a presumptively nonpathogenic SFGR, in all regions surveyed. R. parkeri, previously only detected in Virginia's Amblyomma maculatum ticks, was found in A. americanum in several surveyed areas within two regions having established A. maculatum populations. R. rickettsii was not found in any sample tested. Our study provides the first state-wide screening of A. americanum ticks in recent history and indicates that human exposure to R. amblyommii and to Ehrlichiae may be common. The high prevalence of R. amblyommii, serological cross-reactivity of all SFGR members, and the apparent rarity of R. rickettsii in human biting ticks across the eastern United States suggest that clinical cases of tick-borne disease, including ehrlichiosis, may be commonly misdiagnosed as Rocky Mountain spotted fever, and that suspicion of other SFGR as well as Ehrlichia should be increased. These data may be of relevance to other regions where A. americanum is prevalent.
在过去几十年里，美洲钝眼蜱（Amblyomma americanum）的种群数量在北美有所扩张。它是一种攻击性强且不挑食的叮咬者，是弗吉尼亚州目前最常见的叮咬人类的蜱虫。自20世纪中叶以来，本州针对蜱虫中人类病原体流行情况的研究很少。我们开发了一种六重实时荧光定量PCR检测方法，用于检测三种埃立克体属物种（查菲埃立克体、尤因埃立克体和帕诺拉山埃立克体）以及三种斑点热群立克次体（R. amblyommii、R. parkeri和R. rickettsii），并使用该方法对来自全州各地的美洲钝眼蜱进行检测。我们的研究发现，在所调查的所有地区均存在这三种埃立克体属物种（占比0 - 24.5%），以及一种推测为非致病性斑点热群立克次体R. amblyommii的高流行率（占比50 - 80%）。之前仅在弗吉尼亚州的变异革蜱（Amblyomma maculatum）中检测到过的R. parkeri，在已建立变异革蜱种群的两个地区内的几个调查区域的美洲钝眼蜱中也被发现。在所检测的任何样本中均未发现R. rickettsii。我们的研究提供了近期首次全州范围内对美洲钝眼蜱的筛查，表明人类接触R. amblyommii和埃立克体属物种的情况可能很常见。R. amblyommii的高流行率、所有斑点热群立克次体成员的血清学交叉反应性，以及在美国东部叮咬人类的蜱虫中R. rickettsii明显罕见的情况表明，包括埃立克体病在内的蜱传疾病临床病例可能经常被误诊为落基山斑疹热，并且应该提高对其他斑点热群立克次体以及埃立克体属物种的怀疑。这些数据可能与美洲钝眼蜱流行的其他地区相关。
