Risk assessment and prediction of Ixodes ricinus tick questing activity and human tick-borne encephalitis infection in space and time in the Czech Republic.

Present risk assessment and prediction of future risk of humans exposed to Ixodes (I.) ricinus tick attacks and, consequently, to tick-borne encephalitis (TBE) virus infection as one of the basic preconditions for successful TBE prevention has been intensively studied in the Czech Republic. An atlas of TBE in the Czech Republic containing predictive maps of I. ricinus high-incidence habitats and TBE risk sites identified by satellite data (Landsat 5 TM with spatial resolution 30 m) at a scale of 1:200,000 over a territory of 52,000 km(2) and maps of human TBE case distribution (1971-2000) has been prepared using remote sensing and geographical information systems technologies. The influence of climate changes on a forest ecosystem inhabited by I. ricinus has been studied in the southern region of the Czech Republic. The analysis of long-term series (1931-2000) of climatologic and phenological characteristics has been carried out. The results are compared with the long-term series of TBE incidence. The influence of weather condition on day-to-day changes of I. ricinus host-seeking activities was studied in 2001-2004. Field observations were realized in the south-eastern periphery of Prague where the experimental plots for tick monitoring were established in a relevant type of forest growth (Querceto-carpinetum). I. ricinus activities were investigated by the flagging method on three plots (200 m(2) each) in weekly intervals (March to November) during 2001-2004. The instruments for micrometeorological observations were installed between the experimental plots. Macrometeorological data were used from the nearby Czech Hydrometeorological Institute first class meteorological observatory. Simple and multiple linear regression and quadratic regression were used to test the relation between weather modification and I. ricinus host-seeking activity. Two preliminary most suitable 'models' are demonstrated.

An attempt to elucidate the increased incidence of tick-borne encephalitis and its spread to higher altitudes in the Czech Republic.

In 1993 the incidence of tick-borne encephalitis (TBE) showed a sharp rise in Central Europe and has remained high since--with some slight fluctuation. This increase is clearly evident in the Czech Republic and it could be roughly characterised as twofold in 1993-2001 in comparison with 1984-1992 (5,240:2,441 human cases). As yet in the Czech Republic the TBE increase has been manifested by: a) higher number of cases in areas well known for TBE occurrence in humans; b) re-emergence in areas where TBE human cases were not observed, or only sporadically, for a long time; c) emergence of TBE in places unknown previously (including highly elevated areas). This phenomenon has not been fully elucidated yet and we would like to contribute to a better understanding of its cause by comparing the present situation with historical data. Besides TBE epidemiological data (1965-2001) we use the twenty-year all season dynamics data of Ixodes ricinus host-seeking activity (1953-1972) supplemented by the data in 1982, 1992 and by meteorological data characterising periods under study. The fluctuation in annual averages of I. ricinus occurrence was irregular. These irregularities when compared with meteorological data can be explained by different meteorological conditions in particular years. In corresponding long-time series, the peaks of I. ricinus occurrence and TBE incidence were reached at the same time. Analyses of relevant meteorological data displayed that joint I. ricinus and TBE maximal occurrence values had been preceded by mild (or warm) autumn seasons allowing a prolongation of I. ricinus activities (including development) up to November at least, thus resulting in a higher tick volume the following year. Based on these data we conclude that the increased TBE incidence rates reported in 1993 and afterwards are attributable to a more abundant occurrence of I. ricinus ticks and that their higher abundance is due to modified climatic conditions in the last decade. Such a situation has appeared in the past as well; however, it was rare and in isolated years only. At that time, although the tick population had been more abundant, in the following year it reached the usual level again. In the 1990s the prolonged mild autumn for consecutive several years led to permanently more abundant populations of I. ricinus. The same conclusion explains the shift of I. ricinus occurrence and of TBE distribution to higher altitudes in Sumava and Krkonose Mountains.