Zecken - FSME - Klimawandel: haben wir zuverlässige Daten?
Tick-borne encephalitis is endemic in Europe, in the Far East and in Asia. At present, it is reported regularly in 27 European countries, however with extreme differences in the morbidity rates. For 19 European countries we have reliable data on the TBE incidences since 1976. In these countries, 157,584 TBE cases were registered from 1990 to 2007. If we exclude Russia from this data pool, a total of 50,486 cases remain for Europe (Suss, 2008). In addition to human TBE cases transmitted by tick bites and - more rarely - by milk and milk products, TBE also occurs (more rarely) in dogs, monkeys and horses (Suss et al., 2008b). A steady rise in TBE morbidity was observed over the past 30 years, i. e. 400% from 1976 to 2003 (Suss, 2003; 2008; Randolph, 2004). In a number of "TBE countries" another significant increase was reported from 2004 to 2006. On the other hand, strong fluctuations and a decrease in morbidity have been observed more recently (2007 and 2008) in several European countries. The reasons are unclear (Suss, 2008). It is certain that there are numerous factors which influence these developments. Neglecting the increased awareness of the problem, we can state that almost all social, political, ecological, economic and demographic factors have an impact on the extent of the exposure to tick bites (Suss et al., 2008a). However, in spite of a number of publications on this subject it remains unclear how these many factors interact with each other and how significant they are (Suss and Kahl, 2008). Undoubtedly and supported by the available data, the climate change improves the living conditions of ticks in Europe, especially those of the main vector Ixodes (L) ricinus. This is especially true for an increase in mean temperatures and precipitations, which cause changes in the microclimate that is so important for I. ricinus and other tick species (Gerstengarbe and Werner, 2008). The north- and westward movement of vectors (and pathogens), the increased population density in certain regions, among others caused by an increased availability of hosts and an acceleration of the development cycle, a continued host seeking activity in winter and especially the occurrence of ticks at much higher altitudes in the mountains (meanwhile at up to over 1500 m above sea-level) are measurable factors (Suss et al., 2008b; Dautel et al., 2008; Materna et al., 2008; Gray et al., 2009; Heinz et al., personal commun.). In addition to L ricinus, Dermacentor reticulatus is a good indicator for these changes. The occurrence (or detection?) of newTBE risk areas may be a consequence of these developments. However, science just begins to investigate the molecular epidemiology of TBE virus strains with regard to the geographic distribution of the virus. Although the influence of climate change can be proven reliably, the extent of this influence (e. g. climate change vs. reduction of pollutants in certain regions) is unclear and should be the subject of further investigations