Foley Janet, Rejmanek Daniel, Foley Colin, Matocq Marjorie
Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA; One Health Institute, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Ticks Tick Borne Dis. 2016 Feb;7(1):243-253. doi: 10.1016/j.ttbdis.2015.10.017. Epub 2015 Oct 25.
Dusky-footed woodrats are territorial cricetid rodents that individually occupy large stick houses from which they foray to gather food, find mates, and engage in other activities. These rodents are often bitten by Ixodes spp. ticks and are reservoirs of some strains of tick-borne bacterial pathogens such as Anaplasma phagocytophilum and Borrelia burgdorferi. Limited dispersal by hosts and vectors could create fine-scale population structure where related hosts and pathogen exposure are co-distributed in space. To quantify population genetic structure and infection status, we genotyped 167 woodrats using a panel of 15 microsatellite loci from three northern California study sites: Soquel (SD), Cold Canyon (CC), and Quail Ridge (QR). We used quantitative PCR and serology to test for infection with A. phagocytophilum and B. burgdorferi. All three populations maintained similar, moderately high levels of genetic variation. For A. phagocytophilum, the PCR-prevalence was higher at SD (30.0%) than CC (13%) and QR (7%) whereas the seroprevalence was similar at all three sites (13-18%). The B. burgdorferi PCR-prevalence at CC was 11%, no woodrats were PCR-positive at QR, and none were tested at SD. We found a negative correlation between pairwise genetic relatedness and spatial distance with the majority of highest order relatives occurring within 200m of one another. Related dyads were more likely to be adult females than males, suggesting that adult female residents are the primary source of spatially proximate, high-order relatives in woodrat populations. Despite spatial genetic clustering of hosts, our spatial window test found no significant clustering of pathogens. Woodrats that were seropositive for A. phagocytophilum had higher heterozygosity than seronegative woodrats, which could be consistent with genetically diverse individuals having greater capacity to mount an immune response. Overall, our analyses show that limited dispersal of individual woodrats leads to fine-scale genetic structure within populations. Genetic structure, coupled with the limited dispersal of I. pacificus ticks could result in disease dynamics that are uniquely restricted to small spatial scales. By combining host genetic and disease studies we are able to infer limited dispersal and structured populations among hosts which affect infectious disease clustering and dynamics.
暗足林鼠是具有领地意识的仓鼠科啮齿动物，它们各自占据着大型的木棍房屋，并从这里外出觅食、寻找配偶以及进行其他活动。这些啮齿动物经常被硬蜱属蜱虫叮咬，并且是某些蜱传细菌病原体菌株的宿主，如嗜吞噬细胞无形体和伯氏疏螺旋体。宿主和媒介的有限扩散可能会形成精细尺度的种群结构，使得相关宿主和病原体暴露在空间上共同分布。为了量化种群遗传结构和感染状况，我们使用来自加利福尼亚州北部三个研究地点（索奎尔（SD）、冷峡谷（CC）和鹌鹑岭（QR））的一组15个微卫星位点对167只林鼠进行了基因分型。我们使用定量PCR和血清学方法检测嗜吞噬细胞无形体和伯氏疏螺旋体的感染情况。所有三个种群都保持着相似的、中等程度的高水平遗传变异。对于嗜吞噬细胞无形体，PCR检出率在SD（30.0%）高于CC（13%）和QR（7%），而血清阳性率在所有三个地点相似（13 - 18%）。CC的伯氏疏螺旋体PCR检出率为11%，QR没有林鼠PCR检测呈阳性，SD没有进行检测。我们发现成对遗传相关性与空间距离之间存在负相关，大多数高阶亲属彼此之间的距离在200米以内。相关的成对个体中成年雌性比成年雄性更常见，这表明成年雌性居民是林鼠种群中空间上相邻的高阶亲属的主要来源。尽管宿主存在空间遗传聚类，但我们的空间窗口检验发现病原体没有显著聚类。嗜吞噬细胞无形体血清阳性的林鼠比血清阴性的林鼠具有更高的杂合度，这可能与基因多样化的个体具有更强的免疫反应能力一致。总体而言，我们的分析表明个体林鼠的有限扩散导致了种群内部精细尺度的遗传结构。遗传结构，再加上太平洋硬蜱的有限扩散，可能导致疾病动态在独特的小空间尺度上受到限制。通过结合宿主遗传和疾病研究，我们能够推断宿主之间有限的扩散和结构化种群，这会影响传染病的聚类和动态。
