Borrelia burgdorferi Sensu Lato and Ehrlichia spp. in Ixodes Ticks from Southern Norway

We report the results of a study of the prevalence of Ehrlichia and Borrelia species in 341 questing Ixodes ricinus ticks from two locations in southern Norway. The prevalences of Borrelia burgdorferi sensu lato and Ehrlichia spp. were, respectively, 16 and 11.5% at site 1 and 17 and 6% at site 2. Prevalence and species composition of Borrelia and Ehrlichia varied with location and date of collection. The dominant Borrelia species at both sites was Borrelia afzelii, followed by Borrelia burgdorferi sensu stricto. Borrelia garinii was found in only a single tick. The dominant member of the Ehrlichia group was a recently described Ehrlichia-like organism related to the monocytic ehrlichiae. Variants of Ehrlichia phagocytophila and the agent of human granulocytic ehrlichiosis were also found. The highest prevalences for B. afzelii, B. burgdorferi sensu stricto, and the Ehrlichia-like organism were observed in May. B. afzelii was most prevalent in females, less prevalent in nymphs, and least prevalent in males, while the prevalence of Ehrlichia was highest in nymphs, lower in females, and least in males. Double infections with B. afzelii and B. burgdorferi sensu stricto and with B. afzelii and the Ehrlichia-like organism were significantly overrepresented. Tick densities were highest in May, when densities of more than 200 ticks/100 m(2) were observed, and declined during the summer months to densities as low as 20 ticks/100 m(2). We conclude that estimates of the prevalence of tick-borne bacteria are sensitive to the choice of date and site for collection of ticks. This is the first study of tick-borne Borrelia and Ehrlichia in Norway and the lowest reported B. garinii prevalence in Northern Europe. The prevalence of the Ehrlichia-like organism is described for the first time in questing ticks.

本研究报道了挪威南部两处采集地点的341只活动型蓖麻硬蜱（Ixodes ricinus）中埃立克体属（Ehrlichia）与疏螺旋体属（Borrelia）物种的流行率调查结果。位点1中伯氏疏螺旋体广义复合群（Borrelia burgdorferi sensu lato）与埃立克体属物种的流行率分别为16%与11.5%，位点2则分别为17%与6%。疏螺旋体与埃立克体的流行率及物种组成随采集地点与采集日期存在显著差异。两处位点的优势疏螺旋体物种均为阿氏疏螺旋体（Borrelia afzelii），其次为伯氏疏螺旋体严格群（Borrelia burgdorferi sensu stricto）；伽氏疏螺旋体（Borrelia garinii）仅在1只蜱样本中检出。埃立克体属的优势类群为一种近期被描述的、与单核细胞埃立克体相关的类埃立克体生物，此外还检出了吞噬细胞埃立克体（Ehrlichia phagocytophila）变异株以及人类粒细胞埃立克体病病原体。阿氏疏螺旋体、伯氏疏螺旋体严格群与类埃立克体生物的最高流行率均见于5月。阿氏疏螺旋体的流行率在雌蜱中最高，若蜱次之，雄蜱最低；而埃立克体的流行率则在若蜱中最高，雌蜱次之，雄蜱最低。阿氏疏螺旋体与伯氏疏螺旋体严格群、阿氏疏螺旋体与类埃立克体生物的双重感染比例显著偏高。蜱种群密度在5月达到峰值，每100平方米可达200只以上，夏季期间密度逐渐下降至最低每100平方米仅20只。本研究表明，蜱传细菌流行率的估算结果对蜱的采集日期与采集地点的选择具有敏感性。本研究为挪威境内首次针对蜱传疏螺旋体与埃立克体的调查，且为北欧地区报道的伽氏疏螺旋体最低流行率案例；同时首次在活动蜱样本中描述了类埃立克体生物的流行率。