Multi-source analysis reveals latitudinal and altitudinal shifts in range of Ixodes ricinus at its northern distribution limit

Abstract

BackgroundThere is increasing evidence for a latitudinal and altitudinal shift in the distribution range of Ixodes ricinus. The reported incidence of tick-borne disease in humans is on the rise in many European countries and has raised political concern and attracted media attention. It is disputed which factors are responsible for these trends, though many ascribe shifts in distribution range to climate changes. Any possible climate effect would be most easily noticeable close to the tick's geographical distribution limits. In Norway- being the northern limit of this species in Europe- no documentation of changes in range has been published. The objectives of this study were to describe the distribution of I. ricinus in Norway and to evaluate if any range shifts have occurred relative to historical descriptions.MethodsMultiple data sources - such as tick-sighting reports from veterinarians, hunters, and the general public - and surveillance of human and animal tick-borne diseases were compared to describe the present distribution of I. ricinus in Norway. Correlation between data sources and visual comparison of maps revealed spatial consistency. In order to identify the main spatial pattern of tick abundance, a principal component analysis (PCA) was used to obtain a weighted mean of four data sources. The weighted mean explained 67% of the variation of the data sources covering Norway's 430 municipalities and was used to depict the present distribution of I. ricinus. To evaluate if any geographical range shift has occurred in recent decades, the present distribution was compared to historical data from 1943 and 1983.ResultsTick-borne disease and/or observations of I. ricinus was reported in municipalities up to an altitude of 583 metres above sea level (MASL) and is now present in coastal municipalities north to approximately 69°N.ConclusionI. ricinus is currently found further north and at higher altitudes than described in historical records. The approach used in this study, a multi-source analysis, proved useful to assess alterations in tick distribution.

Range expansion of Ixodes ricinus to higher altitude, and co-infestation of small rodents with Dermacentor marginatus in the Northern Apennines, Italy

“…In the last decades, the geographic range of Ixodes ricinus-the most important vector of tick borne zoonoses (TBZ) in Europe-expanded to previously free areas, including greater latitudes in Northern Europe, as well as greater altitudes in the mountains of Central and Southern Europe (Kirby et al, 2004;Materna et al, 2008;Danielová et al, 2006;Jore et al, 2011;Jaenson et al, 2012;Léger et al, 2012). Immature I. ricinus are commonly found on small rodents, which may play important roles in the transmission of agents of TBZ.…”

Seroprevalence of antibodies to tick-borne encephalitis virus and Anaplasma phagocytophilum in healthy adults from western Norway

“…It is more abundant along the southernmost coastline. In Sogn and Fjordane county, there are more ticks in the western than in the eastern regions [1].…”

The first detection of species of Babesia Starcovici, 1893 in moose, Alces alces (Linnaeus), in Norway

“…Ixodes ricinus is ubiquitous in southern Norway with the highest density near the coast (Mehl 1983, Jore et al 2011. During the past decades, tick abundance has increased and its distribution area expanded further north and to higher altitudes (Jore et al 2011, Medlock et al 2013, Jore et al 2014.…”