Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, Blindern, P.O. Box 1066, 0316, Oslo, Norway.
Norwegian Veterinary Institute, Sentrum, P.O. Box 750, 0106, Oslo, Norway.
Parasit Vectors. 2021 May 13;14(1):254. doi: 10.1186/s13071-021-04775-6.
In Europe, the generalist tick, Ixodes ricinus, is the main vector of several tick-borne pathogens causing diseases in humans and livestock. Understanding how different species of hosts limit the tick population is crucial for management. In general, larger ectoparasites are expected to select hosts with larger body size. Consistent with this, larval and nymphal I. ricinus can feed on a wide range of different-sized vertebrates, while the adult female stage is expected to rely on a medium-large-sized host for reproduction. However, we still have a limited understanding of whether medium-sized hosts other than roe deer can serve as hosts to adult ticks, and other factors than size may also affect host selection.
To increase our understanding of the suitability of the different species of medium-sized hosts for adult ticks, we sampled mainly roadkill mammals from within the questing season of ticks. We counted life stages of ticks on roe deer (Capreolus capreolus) (n = 29), red fox (Vulpes vulpes) (n = 6), badger (Meles meles) (n = 14) and red squirrel (Sciurus vulgaris) (n = 17) from spatially overlapping populations in Norway, and analysed variation between species across different body parts with a mixed-effects negative binomial model (with and without zero-inflation).
Red squirrel hosted a high density of larval and nymphal I. ricinus, but only one individual had adult female ticks. Roe deer hosted by far the largest number of adult ticks. Badgers had very few ticks, possibly due to their thick skin. Red foxes had intermediate numbers, but a high proportion of subcutaneous, dead ticks (69.3%), suggesting they are not very suitable hosts. Body mass predicted the presence of adult I. ricinus ticks. However, species was a better predictor than body mass for number of ticks, suggesting there was species variation in host suitability beyond body mass per se.
Our study provides evidence that roe deer are indeed the main suitable reproduction host to adult I. ricinus ticks, and are likely a key to host limitation of the tick population in this northern ecosystem.
在欧洲，全科 tick，Ixodes ricinus，是几种 tick-borne 病原体的主要载体，这些病原体可导致人类和家畜患病。了解不同宿主物种如何限制 tick 种群对于管理至关重要。一般来说，较大的外寄生虫预计会选择体型较大的宿主。与此一致的是，幼虫和若虫阶段的 I. ricinus 可以吸食各种不同大小的脊椎动物，而雌性成虫阶段预计会依赖中大型宿主进行繁殖。然而，我们仍然对中型宿主以外的鹿是否可以作为成年 tick 的宿主，以及除了体型以外的其他因素是否也会影响宿主选择，了解有限。
为了增加我们对不同中型宿主物种对成年 tick 适宜性的理解，我们主要在 tick 觅食季节内从路边捕杀的哺乳动物中取样。我们在挪威空间重叠的种群中对鹿（Capreolus capreolus）（n=29）、红狐（Vulpes vulpes）（n=6）、獾（Meles meles）（n=14）和红松鼠（Sciurus vulgaris）（n=17）身上计数 tick 的生命阶段，并使用混合效应负二项模型（带和不带零膨胀）分析了不同身体部位的物种间变异。
红松鼠身上有大量的幼虫和若虫阶段的 I. ricinus，但只有一只身上有成年雌性 tick。鹿身上携带的成年 tick 数量最多。獾身上的 tick 非常少，可能是因为它们的皮肤很厚。红狐身上的 tick 数量居中，但有很大比例的皮下、死亡的 tick（69.3%），这表明它们不是很合适的宿主。身体质量预测了成年 I. ricinus tick 的存在。然而，与身体质量相比，物种是 tick 数量的更好预测因子，这表明除了身体质量本身之外，宿主的适宜性存在物种差异。
我们的研究提供了证据表明，鹿确实是成年 I. ricinus tick 的主要适宜繁殖宿主，并且可能是这种北方生态系统中 tick 种群宿主限制的关键。
