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Tick-borne encephalitis virus expansion to higher altitudes correlated with climate warming.

Vlasta Danielová — 2008-04-28T15:35:33-00:00

International journal of medical microbiology : IJMM (21 April 2008)

Since 2002, the expansion of Ixodes ricinus ticks and tick-borne infection agents have been studied in the Krkonose Mts., Czech Republic. Tick-borne encephalitis virus was detected by means of RT-PCR. In 2003, it was detected in 2 out of 491 ticks at 620 and 710-720m a.s.l., respectively, and in 3 out of 939 ticks at 600m a.s.l. at the same locality in 2004. In 2005, tick-borne encephalitis virus was detected in 5 out of 295 ticks at 900-1100m a.s.l., which is above the formerly known altitudinal limit of I. ricinus distribution. The reason for that could be found in the changing climate. Based on the meteorological data collected in the Krkonose Mts., 1961-2005, there was a significant increase in the mean annual temperature (1.3-1.4 degrees C) over that period, namely by 2-3.5 degrees C in May through August. Thus, with respect to the average vertical temperature gradient in summer of about 0.6 degrees C/100m, 2 degrees C correspond to 300-350m in altitude, and accordingly 3.5 degrees C correspond to a shift in altitude of approximately 550-600m, that being in accordance with environmental conditions of the former I. ricinus altitudinal limit confirmed in the Krkonose Mts. 20 years ago.

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

Milan Daniel — 2006-07-23T11:58:07-00:00

International Journal of Medical Microbiology, Vol. 296, No. Supplement 1. (22 May 2006), pp. 41-47.

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 km2 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 m2 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.

Extension of Ixodes ricinus ticks and agents of tick-borne diseases to mountain areas in the Czech Republic

Vlasta Danielova — 2006-07-23T11:52:25-00:00

International Journal of Medical Microbiology, Vol. 296, No. Supplement 1. (22 May 2006), pp. 48-53.

Along with the shift of the hard tick Ixodes ricinus to higher altitudes observed in the Czech Republic a corresponding shift of tick-borne infections to higher altitudes has been expected. Therefore, I. ricinus ticks, mainly nymphs, were investigated for the presence of tick-borne viruses, tick-borne encephalitis (TBE), Tribec and Eyach, and the spirochaete Borrelia burgdorferi sensu lato in the Sumava and Krkonose Mountains (Czech Republic). The TBE virus and different genospecies of B. burgdorferi s.l. were detected by RT-PCR and PCR, respectively. TBE virus was detected in ticks at 620 and 720 m above sea level (a.s.l.), B. burgdorferi s.l. was detected in ticks up to 1065 m a.s.l. Four genospecies of B. burgdorferi s.l. were identified, B. afzelii, B. garinii, B. burgdorferi sensu stricto, and B. valaisiana. Some nymphs carried multiple Borrelia infections. The conditions of tick-borne agents' distribution and potential epidemiological consequences are discussed.

Altitudinal distribution limit of the tick Ixodes ricinus shifted considerably towards higher altitudes in central Europe: results of three years monitoring in the Krkonose Mts. (Czech Republic).

J Materna — 2005-10-25T07:07:21-00:00

Cent Eur J Public Health, Vol. 13, No. 1. (March 2005), pp. 24-28.

The aim of the study was to monitor present status of the Ixodes ricinus tick vertical distribution in the Krkonose Mts. (Czech Republic) and evaluate its potential changes. Two methods were used: monitoring of tick presence on dogs in 2001-2002 and direct monitoring of host-seeking ticks by flagging on two vertical transects reaching from 620 to 1270 m above sea level (a. s. l.) and from 600 to 1020 m in 2002-2003. Moreover ticks were monitored by flagging at another 13 localities situated in 800-1299 m a. s. l. in 2003. Both monitoring methods revealed an obvious shift in altitudinal distribution limit of the tick I. ricinus in the Krkonose Mts. They both showed that ticks recently penetrate even up to a timberline (approximately 1250 m a. s. l.). The number of recorded host-seeking ticks rapidly decreased with increasing altitude. Whereas the average number of recorded nymphs converted per 60 minutes of flagging reached 15.2-25.7 nymphs in 700-799 m a. s. l. and 3.3-23.3 in 800-899 m, it was 4-9.6 nymphs in 900-999 m, 1.5-1.7 nymphs in 1000-1099 m and only 0.2 nymph in 1100-1299 m a. s. l. The observed shift of the tick altitudinal distribution limit at the same time results in extension of areas with potential risk of tick-borne diseases.

Predictive map of Ixodes ricinus high-incidence habitats and a tick-borne encephalitis risk assessment using satellite data.

M Daniel — 2005-08-08T19:18:15-00:00

Exp Appl Acarol, Vol. 22, No. 7. (July 1998), pp. 417-433.

The main objective of this project was to predict Ixodes ricinus abundant habitats reliably as a means of tick-borne encephalitis (TBE) risk assessment for the prevention of this disease. The vegetation types were used as the indicators of an ecosystem suitable for tick occurrence, for TBE virus circulation and, accordingly, for the existence of natural foci of this infection. Remote sensing methods were used to determine the indicative plant cover. Satellite data covering an experimental area of 70 x 70 km in Central Bohemia, the Czech Republic, was acquired by the Landsat 5 TM scanner. Nine forest classes were recognized in the experimental area by successive supervised and unsupervised classifications and identified in a field-checking botanical survey. An epidemiological TBE map based on human cases contracted in the territory under study was exploited for the evaluation of risk in particular forest classes. Predictive maps are expressed both in digital and in printed forms at a scale of 1:300,000 for an overall risk evaluation and at a scale of 1:25,000 for a detailed local orientation.

GIS tools for tick and tick-borne disease occurrence.

M Daniel — 2005-07-24T22:32:25-00:00

Parasitology, Vol. 129 Suppl (2004)

Geographic information systems (GIS), their fundamental components and technologies are described. GIS is a computer-based system enabling the storage, integration, query, display and analysis of data using information on data location. Further, remote sensing (RS) methods and their application in landscape characterization are described. Landscape pattern analysis, combined with statistical analysis, allows the determination of landscape predictors of disease risk. This makes RS/GIS a powerful set of tools for disease surveillance, enabling the prediction of potential disease outbreaks and targeting intervention programs. The 'pre-GIS era' is briefly described including the early mapping of tick distribution, analyses and the display of biogeographical and medical data. The theory of natural focality of diseases (NFD) is explained and its significance in tick-borne diseases (TBD) research is discussed. Many problems of tick ecology and TBD epidemiology and epizootology have been addressed by means of GIS and examples of these studies are presented and discussed.

Tick-borne encephalitis and Lyme borreliosis: comparison of habitat risk assessments using satellite data (an experience from the Central Bohemian region of the Czech Republic).

M Daniel — 2005-07-22T14:17:08-00:00

Cent Eur J Public Health, Vol. 7, No. 1. (February 1999), pp. 35-39.

The vegetation types have been used as the indicators of an ecosystem suitable for high incidence of Ixodes ricinus ticks and their hosts, for the circulation of tick-borne diseases pathogens and, accordingly, for the existence of natural foci of these infections, namely tick-borne encephalitis (TBE) and Lyme borreliosis (LB). The method of remote sensing offers a suitable solution to this problem. We attempted to prepare the habitat risk assessment maps on the territory (11,500 km2) of Central Bohemia (Czech Republic) using Landsat 5 TM imagery. Nine forest classes have been recognized in the satellite data and further identified in a field checking botanical survey. Beside the conclusions dealing with the importance of different plant types for I. ricinus occurrence, also the epidemiological TBE and LB maps based on human cases contracted in the territory under study were exploited for the evaluation of particular forest classes significance, and for the comparison of results achieved. Apart from a general pattern of risk gradation from coniferous to deciduous wood types, both TBE and LB data suggest a specific position of the heterogeneous deciduous wood class (including mainly young deciduous stands and stand ecotones with highly heterogeneous structure). Epidemiological significance of the other particular forest classes was assessed by the degrees of positive class-to-risk associations (see Table 1 and 2).