Centre for Epidemiology and Microbiology, National Institute of Public Health, Prague, Czechia.
Department of Biostatistics, National Institute of Public Health, Prague, Czechia.
Front Cell Infect Microbiol. 2018 Mar 22;8:90. doi: 10.3389/fcimb.2018.00090. eCollection 2018.
Tick-borne encephalitis (TBE) is a serious acute neuroinfection of humans caused by a tick-borne flavivirus. The disease is typically seasonal, linked to the host-seeking activity of (predominantly nymphs), the principal European tick vector species. To address the need for accurate risk predictions of contracting TBE, data on 4,044 TBE cases reported in the Czech Republic during 2001-2006 were compared with questing activity of nymphs monitored weekly at a defined location for the same 6-year period. A time shift of 21 days between infected tick bite and recorded disease onset provided the optimal model for comparing the number of cases of TBE with numbers of questing nymphs. Mean annual distribution of TBE cases and tick counts showed a similar bimodal distribution. Significantly, the ratio of TBE cases to questing nymphs was highest in the summer-autumn period even though the number of questing nymphs peaked in the spring-summer period. However, this pattern changed during a period of extreme meteorological events of flooding and abnormally high temperatures, indicating that changes in climate affect the incidence of TBE. Previous studies failed to link human behavior with changes in incidence of TBE but showed extrinsic temperature impacts arbovirus replication. Hence, we hypothesize the apparent discrepancy between peak nymphal tick activity and greatest risk of contracting TBE is due to the effect of temperature on virus replication in the tick vector. Relative proportions of questing nymphs and the numbers of weeks in which they were found were greater in summer-autumn compared with spring-summer at near-ground temperatures >5°C and at standard day and weekly average temperatures of >15°C. Thus, during the summer-autumn period, the virus dose in infected tick bites is likely greater owing to increased virus replication at higher microclimatic temperatures, consequently increasing the relative risk of contracting TBE per summer-autumn tick bite. The data support the use of weather-based forecasts of tick attack risk (based on daytime ambient temperature) supplemented with weekly average temperature (as a proxy for virus replication) to provide much-needed real-time forecasts of TBE risk.
蜱传脑炎（TBE）是一种由蜱传黄病毒引起的人类严重急性神经感染。这种疾病通常具有季节性，与宿主（主要是若虫）寻找活动有关，这是欧洲主要的蜱传播物种。为了准确预测 TBE 的发病风险，对 2001 年至 2006 年期间在捷克共和国报告的 4044 例 TBE 病例的数据进行了比较，并与同一 6 年期间每周在一个确定地点监测的若虫寻宿主活动进行了比较。受感染蜱叮咬与记录疾病发作之间的 21 天时间差为比较 TBE 病例数量与寻宿主若虫数量提供了最佳模型。TBE 病例和蜱计数的年平均分布呈双峰分布。重要的是，即使寻宿主若虫的数量在春夏季达到峰值，但 TBE 病例与寻宿主若虫的比例在夏秋季最高。然而，这种模式在洪水和异常高温等极端气象事件期间发生了变化，这表明气候变化会影响 TBE 的发病率。先前的研究未能将人类行为与 TBE 发病率的变化联系起来，但表明外间温度会影响虫媒病毒的复制。因此，我们假设在寻宿主若虫活动高峰和感染 TBE 的最大风险之间出现明显差异，是由于温度对蜱媒介中病毒复制的影响。在接近地面温度>5°C 和标准日平均和每周平均温度>15°C的情况下，寻宿主若虫的相对比例和发现它们的周数在夏秋季比春夏季更多。因此，在夏秋季，由于较高微气候温度下病毒复制增加，感染蜱叮咬中的病毒剂量可能更大，从而增加了每夏秋季蜱叮咬感染 TBE 的相对风险。这些数据支持使用基于天气的蜱虫攻击风险预测（基于日间环境温度），并辅以每周平均温度（作为病毒复制的替代指标），以提供急需的 TBE 风险实时预测。
