Ecological conditions of natural foci of tularaemia in the Czech Republic.

Tularaemia, a zoonosis of veterinary and public health importance, commonly occurs in the Czech Republic as well as other countries of Northern Hemisphere. The objective of this study was to analyse the environmental conditions of distribution of natural foci of tularaemia and their long-term persistence in the Czech Republic. A geographic information system has been used for this purpose. A new variable (chi(t)), the mean number of natural foci in a specific area, has been suggested for the evaluation of diseases occurring in natural foci. Comparing two 15-year periods, a close correlation between the geographic distribution and numbers of natural foci of tularaemia in the Czech Republic in 1971-1985 and 1986-2000 (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 (chi(t) = 7.20), geographic areas of up to 200 m of elevation above sea (chi(t) = 9.18), 8.1-10.0 degrees C of mean annual air temperature (chi(t) = 6.24), 450-700 mm of mean annual precipitation (chi(t) = 2.84), and 2001-2200 hour of mean annual sunshine duration (chi(t) = 8.77). It was proved that tularaemia persists in specific areas of natural foci, the general environmental conditions of which can be defined and make it possible to predict the occurrence of tularaemia in other areas of suitable conditions.