The occurrence of the Dermacentor reticulatus tick--its expansion to new areas and possible causes.

The ornate dog tick (Dermacentor reticulatus) can be found in the temperate zones of Eurasia. Its area of occurrence is divided into east and west distributions, although the area as a whole is expanding. The initial east-west division was most probably associated with the varied climatic profile of Europe, for example, the range of specific mean winter and summer temperatures: the region where D. reticulatus is absent is characterized by mean winter temperatures between 0 degree C and 5 degrees C and thin snow cover. The present expansion may be the effect of climate change. The mean temperatures in Europe have increased, the vegetation season has lengthened and positive trends in the number of wet days can be seen. Consequently, northern Europe has become warmer and wetter over the last century. Human activity can also influence the spread of D. reticulatus. The liquidation of habitats suitable for D. reticulatus and the eradication of their hosts can play a role, as can changes in agricultural land use, environmental protection and the spread of international tourism and trade. In summary, the expansion of D. reticulatus into new areas could be the synergistic effect of many favourable factors.