Herrmann Coralie, Gern Lise
Institute of Biology, Laboratory of Eco-Epidemiology of Parasites, University of Neuchâtel, Emile Argand 11, 2000 Neuchâtel, Switzerland.
Ticks Tick Borne Dis. 2013 Sep;4(5):445-51. doi: 10.1016/j.ttbdis.2013.05.002. Epub 2013 Jul 10.
In this study, we tested the survival of Ixodes ricinus under cold conditions in the laboratory. We investigated how the frequency of temperature variations (from -5 °C or -10 °C to 13 °C), and infection with Borrelia burgdorferi sensu lato (s.l.) influenced survival of questing nymphs collected in spring and autumn 2011. In experiment 1, survival of 1760 nymphs was tested at -10 °C over a short period of time to simulate very cold winter conditions. In experiment 2, survival of 1600 nymphs was tested under cold condition (-5 °C) over a long period of time to simulate common winter conditions. Ticks used for survival tests at -5 °C were screened for Borrelia by quantitative PCR, and genospecies identification was achieved by reverse line blotting. Tick age and frequency of temperature variations had a highly significant effect on I. ricinus survival while Borrelia infection was marginally significant. Hence, survival rate was higher in younger (autumn) than older (spring) nymphs and in nymphs exposed to low rather than high-frequency temperature variations. Borrelia-infected ticks tended to survive better than their uninfected counterparts. These findings suggest that in nature (i) frequent temperature changes in winter threaten tick survival more importantly than very low temperatures, (ii) older (spring) ticks are less resistant to cold than younger (autumn) individuals, and (iii) Borrelia infection plays a marginal role in I. ricinus survival during winter conditions.
在本研究中，我们在实验室测试了蓖麻硬蜱在寒冷条件下的存活情况。我们调查了温度变化频率（从-5°C或-10°C到13°C）以及感染广义伯氏疏螺旋体如何影响2011年春、秋季采集的饥饿若蜱的存活。在实验1中，短时间内在-10°C下测试了1760只若蜱的存活情况，以模拟非常寒冷的冬季条件。在实验2中，长时间内在寒冷条件（-5°C）下测试了1600只若蜱的存活情况，以模拟常见的冬季条件。用于-5°C存活测试的蜱通过定量PCR筛查伯氏疏螺旋体，并通过反向线印迹法进行基因种鉴定。蜱的年龄和温度变化频率对蓖麻硬蜱的存活有极显著影响，而伯氏疏螺旋体感染的影响则略显显著。因此，较年轻（秋季）的若蜱比年长（春季）的若蜱存活率更高，暴露于低频温度变化的若蜱比高频温度变化的若蜱存活率更高。感染伯氏疏螺旋体的蜱往往比未感染的蜱存活得更好。这些发现表明，在自然环境中：（i）冬季频繁的温度变化对蜱存活的威胁比极低温度更重要；（ii）年长（春季）的蜱比年轻（秋季）的个体对寒冷的抵抗力更弱；（iii）伯氏疏螺旋体感染在冬季条件下蓖麻硬蜱的存活中起的作用较小。
