Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI, 48824, USA; Program in Ecology, Evolutionary Biology, and Behavior, Michigan State University, East Lansing, MI, 48933, USA.
Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI, 48824, USA; Program in Ecology, Evolutionary Biology, and Behavior, Michigan State University, East Lansing, MI, 48933, USA; Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI, 48933, USA.
Ticks Tick Borne Dis. 2019 Apr;10(3):553-563. doi: 10.1016/j.ttbdis.2019.01.001. Epub 2019 Jan 19.
Most people who contract Lyme borreliosis in the eastern United States (US) acquire infection from the bite of the nymphal life stage of the vector tick Ixodes scapularis, which is present in all eastern states. Yet <5% of Lyme borreliosis cases are reported from outside the north-central and northeastern US. Geographical differences in nymphal questing (i.e., host-seeking behavior) may be epidemiologically important in explaining this latitudinal gradient in Lyme borreliosis incidence. Using field enclosures and a 'common garden' experimental design at two field sites, we directly tested this hypothesis by observing above-litter questing of laboratory-raised nymphal I. scapularis whose parents were collected from 15 locations (= origins) across the species' range. Relative to southern nymphs from origins considered to be of low acarologic risk, northern nymphs from high-risk origins were eight times as likely to quest on or above the surface of the leaf litter. This regional variation in vector behavior (specifically, the propensity of southern nymphs to remain under leaf litter) was highly correlated with Lyme borreliosis incidence in nymphs' counties of origin. We conclude that nymphal host-seeking behavior is a key factor contributing to the low incidence of Lyme borreliosis in southern states. Expansion of northern I. scapularis populations could lead to increased incidence in southern states of Lyme borreliosis and other diseases vectored by this tick, if the 'northern' host-seeking behavior of immigrant nymphs is retained. Systematic surveillance for I. scapularis nymphs questing above the leaf litter in southern states will help predict future geographic change in I. scapularis-borne disease risk.
大多数在美国东部（美国）感染莱姆病的人是从携带病菌的幼虫伊希斯scapularis 的叮咬中感染的，这种幼虫存在于所有东部各州。然而，<5%的莱姆病病例报告来自美国中北部和东北部以外的地区。幼虫求偶（即宿主寻求行为）的地理差异可能在解释莱姆病发病率的纬度梯度方面具有重要的流行病学意义。我们在两个实地地点使用野外围栏和“公共花园”实验设计，通过观察从 15 个地点（=起源地）收集的实验室饲养的幼虫伊希斯 scapularis 的上方求偶行为，直接检验了这一假设。相对于来自被认为低螨虫风险的起源地的南方幼虫，来自高风险起源地的北方幼虫在叶层表面或上方求偶的可能性是南方幼虫的八倍。这种媒介行为（特别是南方幼虫停留在叶层下的倾向）的区域差异与幼虫起源地的莱姆病发病率高度相关。我们得出结论，幼虫宿主寻求行为是导致南部各州莱姆病发病率较低的关键因素。如果移民幼虫保留“北方”宿主寻求行为，北方伊希斯 scapularis 种群的扩张可能导致南部各州莱姆病和其他由这种蜱传播的疾病发病率增加。在南部各州对叶层上方求偶的伊希斯 scapularis 幼虫进行系统监测将有助于预测伊希斯 scapularis 传播疾病风险的未来地理变化。
