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Environ Health Perspect. 2000 Feb;108(2):119-23.

Impact of climatic change on the northern latitude limit and population density of the disease-transmitting European tick Ixodes ricinus.

Author information

1
Natural Resources Management, Department of Systems Ecology, Stockholm University, Stockholm, Sweden. elisa@system.ecology.su.se

Abstract

We examined whether a reported northward expansion of the geographic distribution limit of the disease-transmitting tick Ixodes ricinus and an increased tick density between the early 1980s and mid-1990s in Sweden was related to climatic changes. The annual number of days with minimum temperatures above vital bioclimatic thresholds for the tick's life-cycle dynamics were related to tick density in both the early 1980s and the mid-1990s in 20 districts in central and northern Sweden. The winters were markedly milder in all of the study areas in the 1990s as compared to the 1980s. Our results indicate that the reported northern shift in the distribution limit of ticks is related to fewer days during the winter seasons with low minimum temperatures, i.e., below -12 degrees C. At high latitudes, low winter temperatures had the clearest impact on tick distribution. Further south, a combination of mild winters (fewer days with minimum temperatures below -7 degrees C) and extended spring and autumn seasons (more days with minimum temperatures from 5 to 8 degrees C) was related to increases in tick density. We conclude that the relatively mild climate of the 1990s in Sweden is probably one of the primary reasons for the observed increase of density and geographic range of I. ricinus ticks.

PMID:
10656851
PMCID:
PMC1637900
DOI:
10.1289/ehp.00108119
[Indexed for MEDLINE]
Free PMC Article

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