Department of Veterinary Ecology and Environmental Protection, University of Veterinary and Pharmaceutical Sciences Brno, Brno, Czech Republic
Recently, there have been a growing number of applications of geographic information systems (GIS) in epidemiology and public health. Data for the GIS may be gathered using standard screening methods throughout a distinct territory as well as remote sensing from satellites. GIS databases offer new analytic opportunities for disease assessment and prevention. They have been used to identify risk factors of zoonotic diseases over large geographic areas such as environmental variables associated with the disease and breeding habitats of disease vectors. It is also possible to use GIS to test epidemiological hypotheses about patterns of disease occurrence. It may be stated that GIS make it possible to incorporate space relationships into epidemiological studies of diseases of animals and humans. It is a technology consisting of input, storage, analysis and presentation of geographic data. Using GIS it is possible to combine a whole number of data from various sources and evaluate different aspects of the environment in relation to the phenomenon studied. Analytical possibilities of GIS are still developing and range from a simple visual evaluation of maps to exploratory analysis and modeling. For purposes of veterinary administration and disease control the GIS technology has been used by e.g., Fuchs et al. (2001), McGinn et al. (1996), Michel et al. (2002), Norstrom (2001), Sanson et al. (1991), Schwermer et al. (2002), Solymosi and Medveczky (2000) and Stark et al. (1998). Unlike in domestic animals, the distribution of wild animals in space depends to a great degree on environmental factors and geographic conditions (Pfeiffer and Hugh-Jones, 2002). That is why the GIS technologies are suitable for the purpose of study of occurrence and distribution of diseases in wild animals (Delahay et al., 2000; Conraths et al., 2003). In relation to the growing importance of the so-called "new-emerging" infections (zoonoses) there is an increased interest in the ecology of reservoir hosts (wild rodents and game animals) as well as vectors of diseases. In this respect it is possible to study the geographic distribution of the host, outlining the maximum territory of the disease distribution, the extent of the disease distribution within the distribution of the host, relation between the geographic distribution of the host and the disease within individual habitats, the importance of population ecology of the host (overcrowding, seasonal dynamics, migration activities, activities during the day and night, survival and mortality).
Use of GIS in veterinary medicine is presented here on examples of analysing spatial aspects of distribution of tularaemia, a zoonosis of veterinary and public health importance occurring in natural foci throughout the Northern Hemisphere with the milder biotype B prevailing in Eurasia. In Southern Moravia (Czech Republic) it has been known since autumn 1936 when 290 humans contracted the external ulceroglandular form of the disease due to handling tularaemic hares. During the 1960s, severe epidemics of the professionally-acquired pulmonary form of tularaemia in workers in "cold divisions" of sugar factories occurred. There was a 25-year period of low occurrence of this disease in humans interrupted by another epidemic in 1978. In autumn 1994, the number of tularaemia cases rose again and, during the season of 1998-1999, 115 human cases of tularaemia contracted mainly by handling tularaemic hares were reported (Černý, 2001). These increased numbers of human cases of tularaemia coincide with the rise of seroprevalence of hares positive for tularaemia from the common value of about 1% to 5.75% in 1994. In the last decade, apart from the rise of numbers of positive hares, we have been witnessing some spread of natural foci of tularaemia into more northern areas of Southern Moravia.
1. Ecological conditions of natural foci of tularaemia in the Czech Republic (Pikula et al., 2003): A new variable (xt), the mean number of natural foci in a specific area, has been suggested to analyse the environmental conditions of distribution of natural foci of tularaemia and their long-term persistence in the Czech Republic. Comparing two 15-year periods, a close correlation between the geographic distribution and numbers of natural foci of tularaemia in the Czech Republic in 1971 to 1985 and 1986 to 2000 (r=0.91, n=1814, t=92.50, P=0.01) was found. Natural foci of tularaemia have been persistent, but not stationary, over the period of 30 years and the geographic area of their occurrence has not been considerably growing or diminishing in the Czech Republic. The highest numbers of natural foci of tularaemia were in habitats of alluvial forests (xt=7.20), geographic areas of up to 200 m of elevation above sea (xt=9.18), 8.1-10.0 °C of mean annual air temperature (xt=6.24), 450-700 mm of mean annual precipitation (xt=2.84), and 2001-2200 h of mean annual sunshine duration (xt=8.77).
2. Spatio-temporal aspects of tularaemia in Southern Moravia (Czech Republic) (Pikula et al., 2004): The spatio-temporal development of tularaemia in Southern Moravia (in a selected study area of 130x90 km) was evaluated using correlation analysis which resulted in finding that the geographic distribution of natural foci of tularaemia in any year correlated with the distribution in any other year of the study period of 1994-2001. The coefficients of correlation of all possible combinations of distribution in years 1994-2001 vary from 0.38 to 0.96 (n = 3700, p = 0.01). The closer the years, the closer and more significant the correlation of distribution of tularaemia. It can be stated that, in the study area during the period of eight years, tularaemia persisted rather in the same locations but, as the coefficients of correlation do not equal 1.0, some variation in the distribution could be observed.
3. Ecology of European brown hare and distribution of natural foci of tularaemia in the Czech Republic (Pikula et al., 2004): Quantitative data on the geographic distribution of the European brown hare (a game animal most important as a source of tularaemia for humans in t0068e Czech Republic) were analysed with respect to selected environmental factors and natural foci of tularaemia. The highest population densities of the European brown hare were found in geographic areas of up to 200 m of elevation above sea (231.47 individuals/10km2), climatic district No. 1 (227.91 individuals/10km2), annual snow cover duration of 40-60 days (183.95 individuals/10km2), mean annual precipitation of 450-700 mm (174.71 individuals/10km2), annual sunshine duration of 1801-2000 hour (169.72 individuals/10km2) and mean annual air temperature of over 10.0 °C (245.00 individuals / 10km2). A correlation (r = 0.4431, n = 395, t = 9.7972, P = 0.01) between the population density of the European brown hare and numbers of natural foci of tularaemia in the Czech Republic was found. In other words, tularaemia seems to be the European brown hare population density dependent.
4. Ecology of the common vole and distribution of natural foci of tularaemia (Pikula et al., 2002): The common vole (Microtus arvalis) is another important reservoir animal of tularaemia in the Czech Republic. Analysing the relation between M. arvalis population abundance and geographic distribution and numbers of natural foci of tularaemia in the European hare, it was, however, found that there is no correlation (r = 0.0765, n = 396, t = 1.5228). In other words, tularaemia seems to be independent of M. arvalis population density.
5. Prediction of possible distribution of tularaemia in the Czech Republic (Pikula et al., 2004): A prediction map of tularaemia has been constructed on the basis of the identified factors favourable for the existence of current natural foci of tularaemia in the Czech Republic. Geographic distribution of a total of 6 different factors has been evaluated with respect to their suitability for harbouring natural foci of tularaemia. These factors included habitats of alluvial forests, geographic areas of up to 200 m of elevation above sea, 8.1-10.0°C of mean annual air temperature, 450-700 mm of mean annual precipitation, 1801-2000 and 2001-2200 h of mean annual sunshine duration and highest population densities of the European brown hare (Lepus europaeus). Two main territories of favourable conditions for tularaemia were identified in the Czech Republic, i.e., Southern Moravia and Central Bohemia. Areas of 0, 1, 2, 3, 4, 5 and 6 factors favourable for tularaemia cover 18 120.30, 27 960.75, 15 259.20, 7 933.05, 5 245.35, 3 337.95 and 780.30 km2, respectively, of the total area of 78 636.9 km2 of the Czech Republic.
Conclusion
Prediction modeling of possible occurrence of a zoonosis seems to be an economical way for the selection of areas of study and research. It is also possible to use this knowledge for the purpose of preventive and control measures such as banning transfer of wild animals from areas of existing natural foci to geographic areas where the conditions suitable for the creation of natural foci are met. GIS are suitable for the State Veterinary Administration and they are becoming part of decision-making as knowledge on the geographical aspects of diseases including the distribution of reservoir hosts is essential for disease control.
Acknowledgement
Supported by the Ministry of Education, Youth and Sports of the Czech Republic (Project MSMT 6215712402).
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