Cayol Claire, Koskela Esa, Mappes Tapio, Siukkola Anja, Kallio Eva R
Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FI-40014, Jyväskylä, Finland.
Parasit Vectors. 2017 Mar 31;10(1):166. doi: 10.1186/s13071-017-2112-x.
Tick-borne pathogens pose an increasing threat to human and veterinary health across the northern hemisphere. While the seasonal activity of ticks is largely determined by climatic conditions, host-population dynamics are also likely to affect tick abundance. Consequently, abundance fluctuations of rodents in northern Europe are expected to be translated into tick dynamics, and can hence potentially affect the circulation of tick-borne pathogens. We quantified and explained the temporal dynamics of the tick Ixodes ricinus in the northernmost part of its European geographical range, by estimating (i) abundance in vegetation and (ii) infestation load in the most common rodent species in the study area, the bank vole Myodes glareolus.
Ixodes ricinus nymphs and adult females, the life stages responsible for the most of tick bites in humans, peaked in May-June and August-September. Larvae and nymphs were simultaneously active in June and abundance of questing larvae and nymphs in the vegetation showed a positive association with bank vole abundance. Moreover, infesting larvae and nymphs were aggregated on bank voles, and the infestation of bank voles with I. ricinus larvae and nymphs was positively associated with bank vole abundance.
Our results indicate early summer and early autumn as periods of increased risk for humans to encounter I. ricinus ticks in boreal urban forests and suggest a 2 years life-cycle for I. ricinus with two cohorts of ticks during the same year. Moreover, we identified a simultaneous activity of larvae and nymphs which allows co-feeding on the rodent host, which in turn supports the transmission of several important zoonotic tick-borne pathogens. Finally, we showed that a high density of the rodent host may enhance the risk that ticks and, potentially, tick-borne pathogens pose to human health.
蜱传病原体对北半球的人类和兽医健康构成了日益严重的威胁。虽然蜱的季节性活动在很大程度上由气候条件决定，但宿主种群动态也可能影响蜱的数量。因此，预计北欧啮齿动物数量的波动会转化为蜱的动态变化，从而可能影响蜱传病原体的传播。我们通过估计（i）植被中的数量和（ii）研究区域内最常见啮齿动物物种——小林姬鼠（Myodes glareolus）的感染负荷，对欧洲地理范围内最北部地区蓖麻硬蜱（Ixodes ricinus）的时间动态进行了量化和解释。
蓖麻硬蜱的若虫和成年雌蜱是导致人类被蜱叮咬的主要阶段，它们在5 - 6月和8 - 9月达到高峰。幼虫和若虫在6月同时活跃，植被中寻觅的幼虫和若虫数量与小林姬鼠数量呈正相关。此外，寄生的幼虫和若虫在小林姬鼠身上聚集，小林姬鼠被蓖麻硬蜱幼虫和若虫寄生的情况与小林姬鼠数量呈正相关。
我们的结果表明，在北方城市森林中，人类在初夏和初秋遇到蓖麻硬蜱的风险增加，并表明蓖麻硬蜱的生命周期为2年，且同年有两代蜱。此外，我们发现幼虫和若虫同时活动，这使得它们能够在啮齿动物宿主上共同取食，进而支持了几种重要的人兽共患蜱传病原体的传播。最后，我们表明啮齿动物宿主的高密度可能会增加蜱以及潜在的蜱传病原体对人类健康构成的风险。
