Abstract
BackgroundThe incidence of tick-borne encephalitis showed a dramatic spike in several countries in Europe in 2006, a year that was unusually cold in winter but unusually warm and dry in summer and autumn. In this study we examine the possible causes of the sudden increase in disease: more abundant infected ticks and/or increased exposure due to human behaviour, both in response to the weather.MethodsFor eight countries across Europe, field data on tick abundance for 2005–2007, collected monthly from a total of 41 sites, were analysed in relation to total annual and seasonal TBE incidence and temperature and rainfall conditions.ResultsThe weather in 2006–2007 was exceptional compared with the previous two decades, but neither the very cold start to 2006, nor the very hot period from summer 2006 to late spring 2007 had any consistent impact on tick abundance. Nor was the TBE spike in 2006 related to changes in tick abundance. Countries varied in the degree of TBE spike despite similar weather patterns, and also in the degree to which seasonal variation in TBE incidence matched seasonal tick activity.ConclusionThe data suggest that the TBE spike was not due to weather-induced variation in tick population dynamics. An alternative explanation, supported by qualitative reports and some data, involves human behavioural responses to weather favourable for outdoor recreational activities, including wild mushroom and berry harvest, differentially influenced by national cultural practices and economic constraints.
Highlights
The incidence of tick-borne encephalitis showed a dramatic spike in several countries in Europe in 2006, a year that was unusually cold in winter but unusually warm and dry in summer and autumn
The best explanation for this tick-borne encephalitis (TBE) spike in Czechland has centred around the unusual weather conditions of 2006, that are suggested to have improved tick survival over winter, accelerated the increase in spring questing activity by ticks, and encouraged more recreational activity by humans in tick-infested forests, as conditions were especially favourable for good mushroom crops [1,2]
The unusually warm summer started as early as June in Switzerland, Bavaria (Germany) and Slovenia (Figure 3); it was least marked in Latvia (Figure 4), where only September and December were exceptionally warm, and the reversal in August was least marked in Latvia, Lithuania and NE Poland, and Estonia
Summary
The incidence of tick-borne encephalitis showed a dramatic spike in several countries in Europe in 2006, a year that was unusually cold in winter but unusually warm and dry in summer and autumn. The best explanation for this TBE spike in Czechland has centred around the unusual weather conditions of 2006 (described below), that are suggested to have improved tick survival over winter, accelerated the increase in spring questing activity by ticks, and encouraged more recreational activity by humans in tick-infested forests, as conditions were especially favourable for good mushroom crops [1,2]. In some respects, this seems intuitively plausible.
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