Extension of Ixodes ricinus ticks and agents of tick-borne diseases to mountain areas in the Czech Republic
Introduction
In the early 1990s, the incidence of tick-borne encephalitis (TBE) rose sharply in Europe and has remained high since, with some slight fluctuation (for a synopsis see http://www.tbe-info.com/epidemiology/index.html). In the Czech Republic, the emergence of TBE in new areas including higher altitudes has been observed (Daniel et al., 2003). Research in the field revealed that the major factor is climate-related changes (Daniel et al., 2004). The influence of climate change on Ixodes ricinus distribution in Sweden was documented (Lindgren and Gustafson, 2001). This phenomenon was observed also in Denmark (Skarphédinsson et al., 2005) and in Norway (Skarpaas et al., 2004).
The vertical limit of I. ricinus distribution in European countries differs according to geographical position and it increases with decreasing geographical latitude (Filippova, 1977). In former time, the vertical limit of I. ricinus occurrence in the Czech Republic was considered 700–800 m above sea level (a.s.l.) based on the research which covered almost the whole territory of the Czech Republic in 1960–1962. The research was coordinated on the governmental level (Černý et al., 1965). In 1959, we monitored ectoparasites on small mammals (included ticks) in the eastern part of Šumava Mts. Results confirmed the above-mentioned altitudinal limit (unpublished data). In 1981–1983, that limit was further confirmed in a long-term field experiment in the Krkonoše Mountains (Giant Mts.) (Daniel et al., 1988; Daniel, 1993). The altitudinal limit of I. ricinus occurrence was consequently accepted as the limit of risk of acquiring tick-borne diseases. At that time, the incidence of TBE cases was consistent with this conclusion. Thus, there is sufficient historical data to make a comparison with the situation today.
In 2001 and 2002, attention was directed to the Šumava Mts. at the southern boundary of the Czech Republic with Germany and Austria, because there human cases of TBE had been identified in places exceeding the known uppermost altitude of risk (Daniel et al., 2003). Also the healthcare and forestry staff of the Šumava National Park observed I. ricinus to occur in localities at higher altitudes than had previously been found. In the years 2002 and 2003, the upper limits of I. ricinus distribution were studied in detail in the Krkonoše National Park in the highest Czech mountain range at the Polish border. In both cases, a marked vertical shift to higher altitudes (by up to 500 m) was found. This study attempted to answer the question, whether or not there has also been a shift to higher altitudes in the distribution of the tick-borne disease agents, TBE virus and Borrelia burgdorferi sensu lato.
Section snippets
Two territories under study
The two mountain ranges differ due to their different geological origin. The Šumava Mts. of Archean origin are characterized by extensive so-called Šumava plains in an altitude around 1000 m a.s.l., covering approximately 40% of the whole mountain extent, with single rounded summits over 1200 m, and with rough climatic conditions. In the central part of the Plains (Kvilda, 1050 m a.s.l.), a mean annual temperature of +2 °C, a minimum temperature of −41.6 °C (January 30, 1987), and a maximum of 30.8
Results
I. ricinus ticks were collected between 760 and 1080 m a.s.l. in the Šumava Mts. and between 600 and 1270 m a.s.l. in the Krkonoše Mts. The decrease of tick abundance with increasing altitude is evident (Table 1).
In 2002, 372 I. ricinus ticks (246 nymphs, 61 females, 65 males) from 762 to 860 m a.s.l. in the Šumava Mts. and 294 I. ricinus nymphs from 600 to 1180 m a.s.l. in the Krkonoše Mts. were examined for various tick-borne arboviruses. The results were negative. In 2003, TBE virus was detected
Discussion
B. burgdorferi s.l. occurrence in I. ricinus ticks in both studied areas and two TBE human infections acquired at 900 m a.s.l. in the Šumava Mts. indicate the risk of getting tick-borne infections in altitudes regarded free of that risk, as yet (Daniel et al., 2003). This is important information for the public health service, since many attractive destinations inviting for outdoor activities especially in the main tick activity season are situated at that altitude. Engorged I. ricinus ticks had
Acknowledgements
It is a pleasure to thank to Dr. J. Noz˘ička, District Public Health Centre, Prachatice, and Ing. A. Jirsa, Administration of the Šumava National Park, Vimperk, for their aid in this investigation. This study was partly supported by WHO/EC project ‘Climate Change and Adaptation Strategies for Human Health in Europe’ (cCASHh), Contract no. EVK2–2000–0070. We are very grateful to Prof. D. Crossley, University of Georgia, Athens, USA, for linguistic review of the manuscript.
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