Climate and environmental change drives Ixodes ricinus geographical expansion at the northern range margin

Solveig Jore,Ketil Isaksen,Edgar Brun,Bernt Johansen,Bjørnar Ytrehus,Zerai Woldehiwet,Merete Hofshagen,Hege Brun-Hansen,Hildegunn Viljugrein,Inger-Lise Larsen,Sophie O Vanwambeke,Sebastian Westermann,Anja B Kristoffersen

doi:10.1186/1756-3305-7-11

Abstract

BackgroundGlobal environmental change is causing spatial and temporal shifts in the distribution of species and the associated diseases of humans, domesticated animals and wildlife. In the on-going debate on the influence of climate change on vectors and vector-borne diseases, there is a lack of a comprehensive interdisciplinary multi-factorial approach utilizing high quality spatial and temporal data.MethodsWe explored biotic and abiotic factors associated with the latitudinal and altitudinal shifts in the distribution of Ixodes ricinus observed during the last three decades in Norway using antibodies against Anaplasma phagocytophilum in sheep as indicators for tick presence. Samples obtained from 2963 sheep from 90 farms in 3 ecologically different districts during 1978 – 2008 were analysed. We modelled the presence of antibodies against A. phagocytophilum to climatic-, environmental and demographic variables, and abundance of wild cervids and domestic animals, using mixed effect logistic regressions.ResultsSignificant predictors were large diurnal fluctuations in ground surface temperature, spring precipitation, duration of snow cover, abundance of red deer and farm animals and bush encroachment/ecotones. The length of the growth season, mean temperature and the abundance of roe deer were not significant in the model.ConclusionsOur results highlight the need to consider climatic variables year-round to disentangle important seasonal variation, climatic threshold changes, climate variability and to consider the broader environmental change, including abiotic and biotic factors. The results offer novel insight in how tick and tick-borne disease distribution might be modified by future climate and environmental change.

Highlights

Global environmental change is causing spatial and temporal shifts in the distribution of species and the associated diseases of humans, domesticated animals and wildlife
We focused on factors affecting survival and reproduction success of ticks, namely climate, bush encroachment, demography, abundance of cervids and farm animals
Study design Three study districts were selected in Southern Norway (INLAND, COAST and FJORD) which differ with respect to historical tick presence, topography, demography of human and animal population, bush encroachment, presence of cervids and degree of climate change

Summary

Introduction

Global environmental change is causing spatial and temporal shifts in the distribution of species and the associated diseases of humans, domesticated animals and wildlife. Beyond changes in the absolute levels of environmental variables, the probable changes in variability between seasons have been highlighted [9,10] These climatic changes could influence the life cycle of I. ricinus, we lack clear evidence for a consistent association between tick abundance and a warmer and wetter climate [11]. Other environmental variables such as landscape characteristics and abundance of hosts are important drivers of tick population dynamics [12,13] and might modify or mask climatic factor effects [14,15]

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Discussion

Conclusion