Walker A R, Alberdi M P, Urquhart K A, Rose H
Royal (Dick) School of Veterinary Studies, University of Edinburgh, Scotland.
Med Vet Entomol. 2001 Mar;15(1):40-9. doi: 10.1046/j.1365-2915.2001.00271.x.
Ixodes ricinus L. (Acari: Ixodida) were sampled during 1996-99 in southern Scotland, on vegetation using cloth drags, on humans by removal from clothing and on roe deer (Capreolus capreolus L.) by searching legs of culled deer. Developmental microclimate was recorded by automatic recorders and questing microclimate by portable instruments during tick collections. Ticks and deer were examined for infection with Ehrlichia phagocytophila bacteria (Rickettsiales) using microscopy and polymerase chain reaction. This pathogen causes tick-borne fever of sheep in Europe and human granulocytic ehrlichiosis in North America, but in Europe human clinical ehrlichiosis due to E. phagocytophila has not been recorded despite serological evidence of exposure. Among three types of habitat, coniferous woodland was most infested with questing ticks (560 ticks/km of drag; mean numbers collected on long trousers: 24.3 larvae, 13.5 nymphs and 0.8 adult ticks/km walked), deciduous woodland had slightly lower infestation (426 ticks/km drag) and upland sheep pasture had much lower infestation (220 ticks/km drag). Of the three main vegetation types, bracken was least infested (360 ticks/km drag), ericas most (430 ticks/km drag) and grassland had intermediate infestation density (413 ticks/km drag). Questing and developmental microclimates were poor predictors of exposure within these habitats, except lower infestation of pastures was attributed to greater illumination there. Collectors who walked a total of 300 km through all habitats (taking 360 h in all seasons), wearing cotton trousers hanging outside rubber boots, were bitten by only four nymphs and 11 larvae of I. ricinus (but no adult ticks). There was a negative correlation between densities of deer and ticks collected, although presence of deer remains a major indicator of exposure. The proportion of infected ticks was fairly uniform at four sites studied. Overall prevalence of E. phagocytophila in I. ricinus was 3.3% in nymphs (40/1203) but only approximately 1.5% in adults of both sexes (although males do not bite). It was estimated that nymphs of I. ricinus gave 4.4% probability of one infected bite/person/year (for occupational exposure during this research) due to presence in all seasons and habitats, their human biting rate of 0.011 nymphs/h or 0.013 nymphs/km and widespread infection with E. phagocytophila. The frequency distribution of intensity of infection in ticks was approximately normal (mean 98 morulae/nymph infected), thus there is a high risk of receiving a high dose from any one infected tick bite.
1996年至1999年期间，在苏格兰南部对蓖麻硬蜱（Ixodes ricinus L.，蜱螨亚纲：硬蜱目）进行了采样，在植被上用布拖法采集，在人体上从衣物上采集，在狍（Capreolus capreolus L.）上通过检查被扑杀鹿的腿部采集。在蜱虫采集期间，发育微气候由自动记录仪记录，寻觅微气候由便携式仪器记录。使用显微镜和聚合酶链反应检查蜱虫和鹿是否感染嗜吞噬细胞埃立克体细菌（立克次氏体目）。这种病原体在欧洲引起绵羊的蜱传发热，在北美引起人类粒细胞埃立克体病，但在欧洲，尽管有血清学证据表明存在暴露，但尚未记录到由嗜吞噬细胞埃立克体引起的人类临床埃立克体病。在三种栖息地类型中，针叶林中有寻觅蜱虫的情况最为严重（每公里拖行采集到560只蜱虫；在长裤上采集到的平均数量：每公里行走采集到24.3只幼虫、13.5只若虫和0.8只成年蜱虫），落叶林的蜱虫侵扰程度略低（每公里拖行采集到426只蜱虫），高地绵羊牧场的侵扰程度低得多（每公里拖行采集到220只蜱虫）。在三种主要植被类型中，蕨菜的蜱虫侵扰程度最低（每公里拖行采集到360只蜱虫），欧石南最多（每公里拖行采集到430只蜱虫），草地的侵扰密度居中（每公里拖行采集到413只蜱虫）。除了牧场侵扰程度较低归因于那里光照较强外，寻觅和发育微气候并不能很好地预测这些栖息地内的暴露情况。在所有季节中总共步行300公里穿越所有栖息地（总共耗时360小时）的采集者，穿着外面套着橡胶靴的棉质长裤，仅被4只蓖麻硬蜱若虫和11只幼虫叮咬（但没有成年蜱虫）。采集到的鹿和蜱虫的密度之间存在负相关，尽管鹿的存在仍然是暴露的主要指标。在所研究的四个地点，感染蜱虫的比例相当均匀。蓖麻硬蜱若虫中嗜吞噬细胞埃立克体的总体患病率为3.3%（40/1203），但两性成年蜱虫中仅约为1.5%（尽管雄性不叮咬）。据估计，由于蓖麻硬蜱若虫全年存在于所有栖息地，其对人类叮咬率为每小时0.011只若虫或每公里0.013只若虫，且广泛感染嗜吞噬细胞埃立克体，因此蓖麻硬蜱若虫导致每人每年因受感染叮咬而感染的概率为4.4%（针对本研究中的职业暴露）。蜱虫感染强度的频率分布大致呈正态分布（平均每只感染若虫有98个桑葚体），因此单次被感染蜱虫叮咬就有很高风险接受高剂量感染。
