Driving forces for changes in geographical distribution of Ixodes ricinus ticks in Europe

Abstract

Many factors are involved in determining the latitudinal and altitudinal spread of the important tick vector Ixodes ricinus (Acari: Ixodidae) in Europe, as well as in changes in the distribution within its prior endemic zones. This paper builds on published literature and unpublished expert opinion from the VBORNET network with the aim of reviewing the evidence for these changes in Europe and discusses the many climatic, ecological, landscape and anthropogenic drivers. These can be divided into those directly related to climatic change, contributing to an expansion in the tick’s geographic range at extremes of altitude in central Europe, and at extremes of latitude in Scandinavia; those related to changes in the distribution of tick hosts, particularly roe deer and other cervids; other ecological changes such as habitat connectivity and changes in land management; and finally, anthropogenically induced changes. These factors are strongly interlinked and often not well quantified. Although a change in climate plays an important role in certain geographic regions, for much of Europe it is non-climatic factors that are becoming increasingly important. How we manage habitats on a landscape scale, and the changes in the distribution and abundance of tick hosts are important considerations during our assessment and management of the public health risks associated with ticks and tick-borne disease issues in 21st century Europe. Better understanding and mapping of the spread of I. ricinus (and changes in its abundance) is, however, essential to assess the risk of the spread of infections transmitted by this vector species. Enhanced tick surveillance with harmonized approaches for comparison of data enabling the follow-up of trends at EU level will improve the messages on risk related to tick-borne diseases to policy makers, other stake holders and to the general public.

The wild life of tick-borne pathogens

“…This, together with a large distribution in suitable habitat and climatic conditions, explains why I. ricinus has such a wide distribution, and why it occurs in high densities in many areas with a vertebrate assemblage existing of widespread species. It also supports the hypothesis that the increase in Lyme borreliosis may be due to an increase in I. ricinus distribution and abundance 39,61 , following increases in range and abundance of widespread host species such as Bank vole, Blackbird and Roe deer [147][148][149] .…”

“…Ixodes ricinus populations have expanded and increased in density over the last couple of decades 61 . This can partly be explained by an increase in population size of the most important host species (Bank vole, Blackbird, Red deer, Roe deer, and Wood mouse) in Europe [147][148][149] .…”

“…From these, the spirochaete complex Borrelia burgdorferi sensu lato 58 (from here on referred to as B. burgdorferi), the causative agent of Lyme borreliosis and vectored by ticks of the Ixodes ricinus complex 59 , causes the majority of human disease cases 60 . Both in Europe and in North America, I. ricinus and I. scapularis populations have spread and increased in density in recent decades, most probably due to a multitude of man-made changes to the environment, which has resulted in an increase in Lyme disease incidence 49,61 . Lyme disease risk is determined by multiple biological, environmental and societal factors 8,62,63 .…”

Autochthonous Babesia canis, Hepatozoon canis and imported Babesia gibsoni infection in dogs in the Czech Republic

“…The most commonly discussed reasons include the changing ecology of ticks (Medlock et al 2013;Pfaffle et al 2013;Foldvari et al 2016;Rubel et al 2016) and international travel or transport of infected animals (Hamel et al 2011). Both of these situations apply also for the Czech Republic (Kucera 1992;Svobodova and Svobodova 2004;Materna et al 2008).…”

The Role of Game (Wild Boar and Roe Deer) in the Spread of Tick-Borne Encephalitis in the Czech Republic

“…Medlock et al (2013) in his review concluded that increased host abundance leading to enhanced tick reproduction in endemic zones and dispersal of roe deer at higher altitude and latitude are key drivers for change in geographical distribution of I. ricinus ticks in Europe. High reproductive potential of roe deer and the capability for disseminating infected ticks to distant areas, far away from the original endemic area, were behind the spread of TBE to the North of Sweden ( Jaenson et al 2012).…”