Department of Biodiversity and Molecular Ecology, Research and Innovation Centre, Fondazione Edmund Mach, via E. Mach 1, I-38010 San Michele all'Adige, Trento, Italy.
Int J Parasitol. 2012 Apr;42(4):365-72. doi: 10.1016/j.ijpara.2012.02.012. Epub 2012 Mar 21.
Tick borne encephalitis (TBE) is endemic to eastern and central Europe with broad temporal and spatial variation in infection risk. Although many studies have focused on understanding the environmental and socio-economic factors affecting exposure of humans to TBE, comparatively little research has been devoted to assessing the underlying ecological mechanisms of TBE occurrence in enzootic cycles, and therefore TBE hazard. The aim of this study was to evaluate the effect of the main ungulate tick hosts on the pattern of tick infestation in rodents and TBE occurrence in rodents and questing adult ticks. In this empirical study, we considered three areas where endemic human TBE occurs and three control sites having no reported human TBE cases. In these six sites located in Italy and Slovakia, we assessed deer density using the pellet group count-plot sampling technique, collected questing ticks, live-trapped rodents (primarily Apodemus flavicollis and Myodes glareolus) and counted ticks feeding on rodents. Both rodents and questing ticks were screened for TBE infection. TBE infection in ticks and rodents was positively associated with the number of co-feeding ticks on rodents and negatively correlated with deer density. We hypothesise that the negative relationship between deer density and TBE occurrence on a local scale (defined by the minimum overlapping area of host species) could be attributed to deer (incompetent hosts) diverting questing ticks from rodents (competent hosts), know as the 'dilution effect hypothesis'. We observed that, after an initial increase, the number of ticks feeding on rodents reached a peak for an intermediate value of estimated deer density and then decreased. Therefore, while at a regional scale, tick host availability has already been shown to be directly correlated with TBE distribution, our results suggest that the interactions between deer, rodents and ticks are much more complex on a local scale, supporting the possibility of a dilution effect for TBE.
蜱传脑炎（TBE）流行于东欧和中欧，其感染风险在时间和空间上都有很大的变化。尽管许多研究都集中在了解影响人类接触 TBE 的环境和社会经济因素上，但相对较少的研究致力于评估在地方性循环中 TBE 发生的潜在生态机制，以及因此 TBE 危害。本研究旨在评估主要有蹄类蜱宿主对啮齿动物蜱类感染模式和啮齿动物及游离成蜱 TBE 发生的影响。在这项实证研究中，我们考虑了三个人类地方性 TBE 发生地区和三个没有报告人类 TBE 病例的对照地区。在这六个位于意大利和斯洛伐克的地点，我们使用粪便组计数样方采样技术评估鹿的密度，收集游离成蜱，用活捕器捕获啮齿动物（主要是黄腹草原田鼠和黑线姬鼠）并计算寄生在啮齿动物上的蜱数。同时对啮齿动物和游离成蜱进行 TBE 感染检测。蜱和啮齿动物的 TBE 感染与啮齿动物上共食蜱的数量呈正相关，与鹿的密度呈负相关。我们假设，在当地尺度（由宿主物种的最小重叠面积定义）上，鹿密度与 TBE 发生之间的负相关关系可能归因于鹿（非胜任宿主）将游离成蜱从啮齿动物（胜任宿主）身上转移，这被称为“稀释效应假说”。我们观察到，在最初增加后，寄生在啮齿动物上的蜱数量达到估计鹿密度的中间值时达到峰值，然后减少。因此，虽然在区域尺度上，蜱宿主的可利用性已被证明与 TBE 分布直接相关，但我们的结果表明，鹿、啮齿动物和蜱之间的相互作用在当地尺度上要复杂得多，支持 TBE 存在稀释效应的可能性。
