Lane Robert S, Fedorova Natalia, Kleinjan Joyce E, Maxwell Matthew
Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA.
Ticks Tick Borne Dis. 2013 Sep;4(5):377-85. doi: 10.1016/j.ttbdis.2013.02.005. Epub 2013 May 3.
Little is known about the eco-epidemiology of Lyme disease in southern California, a region where the incidence is much lower than it is in northern California. Here, we sought to discover the previously unknown microhabitats of nymphs of the primary vector, the western black-legged tick (Ixodes pacificus), in 3 moderately to heavily-utilized state parks in the Santa Monica Mountains in Los Angeles County; to elucidate the seasonal distribution and abundance of adults of I. pacificus and another human-biter, the Pacific Coast tick (Dermacentor occidentalis); and to determine what Lyme-disease or relapsing-fever group borreliae are present in questing nymphs or adult ticks. I. pacificus nymphs were collected infrequently at various times of day in 2 chaparral or 7 woodland litter areas by dragging (combined mean=0.4 nymphs per hour). The western fence lizard (Sceloporus occidentalis) was a choice sentinel animal for detecting the presence of I. pacificus nymphs (and larvae) in diverse biotopes even when dragging litter in them was fruitless. The abundance and seasonality of I. pacificus and D. occidentalis adults resembled what had been documented previously for these ticks in northern California. Overall, zero of 27 free-living and 118 lizard-infesting I. pacificus nymphs, 7 (0.29%) of 2392 I. pacificus adults and 2 (0.22%) of 896 D. occidentalis adults were infected with Borrelia burgdorferi sensu lato (Bb sl), but none of them harbored B. miyamotoi, a relapsing-fever group spirochete implicated recently as a zoonotic pathogen in Russia. Borrelia americana and the human pathogen B. burgdorferi sensu stricto were each detected in one (0.04%), and uncharacterized Bb sl in 5 adult I. pacificus (0.21%) that clustered with B. americana. Both PCR-positive D. occidentalis adults contained B. burgdorferi sensu stricto. We conclude that the acarologic risk of being bitten by a B. burgdorferi sensu lato-infected ixodid tick in the habitats studied is slight, which offers a plausible explanation for the low reported incidence of Lyme disease in south coastal California.
关于南加州莱姆病的生态流行病学，人们知之甚少，该地区的发病率远低于北加州。在此，我们试图在洛杉矶县圣莫尼卡山脉3个中度至重度利用的州立公园中，发现主要病媒西方黑腿蜱（太平洋硬蜱）若虫此前未知的微生境；阐明太平洋硬蜱成虫以及另一种叮人蜱——太平洋海岸蜱（西方革蜱）的季节性分布和丰度；并确定在觅食的若虫或成年蜱中存在哪些莱姆病或回归热群疏螺旋体。通过拖网采集，在2个丛林或7个林地落叶区域，于一天中的不同时间偶尔能采集到太平洋硬蜱若虫（综合平均值为每小时0.4只若虫）。西部围栏蜥蜴是一种理想的哨兵动物，可用于检测不同生物群落中太平洋硬蜱若虫（和幼虫）的存在，即便在其中拖网采集落叶无果时也是如此。太平洋硬蜱和西方革蜱成虫的丰度及季节性与此前北加州对这些蜱的记录相似。总体而言，27只自由生活的太平洋硬蜱若虫和118只寄生于蜥蜴的若虫中，没有一只感染伯氏疏螺旋体狭义种（Bb sl），2392只太平洋硬蜱成虫中有7只（0.29%）、896只西方革蜱成虫中有2只（0.22%）感染了伯氏疏螺旋体狭义种，但它们均未携带米氏疏螺旋体，这是一种回归热群螺旋体，最近在俄罗斯被认定为人畜共患病原体。在一只太平洋硬蜱成虫（0.04%）中检测到美洲疏螺旋体和人类病原体伯氏疏螺旋体狭义种，在5只成年太平洋硬蜱（0.21%）中检测到未分类的Bb sl，这些成年蜱与美洲疏螺旋体聚类。两只PCR检测呈阳性的西方革蜱成虫均含有伯氏疏螺旋体狭义种。我们得出结论，在所研究的栖息地中，被感染伯氏疏螺旋体狭义种的硬蜱叮咬的螨学风险很低，这为南加州沿海地区莱姆病报告发病率低提供了一个合理的解释。
