Changes in the geographical distribution and abundance of the tick Ixodes ricinus during the past 30 years in Sweden

<p>Abstract</p> <p>Background</p> <p><it>Ixodes ricinus </it>is the main vector in Europe of human-pathogenic Lyme borreliosis (LB) spirochaetes, the tick-borne encephalitis virus (TBEV) and other pathogens of humans and domesticated mammals. The results of a previous 1994 questionnaire, directed at people living in Central and North Sweden (Svealand and Norrland) and aiming to gather information about tick exposure for humans and domestic animals, suggested that <it>Ixodes ricinus </it>ticks had become more widespread in Central Sweden and the southern part of North Sweden from the early 1980s to the early 1990s. To investigate whether the expansion of the tick's northern geographical range and the increasing abundance of ticks in Sweden were still occurring, in 2009 we performed a follow-up survey 16 years after the initial study.</p> <p>Methods</p> <p>A questionnaire similar to the one used in the 1994 study was published in Swedish magazines aimed at dog owners, home owners, and hunters. The questionnaire was published together with a popular science article about the tick's biology and role as a pathogen vector in Sweden. The magazines were selected to get information from people familiar with ticks and who spend time in areas where ticks might be present.</p> <p>Results</p> <p>Analyses of data from both surveys revealed that during the near 30-year period from the early 1980s to 2008, <it>I. ricinus </it>has expanded its distribution range northwards. In the early 1990s ticks were found in new areas along the northern coastline of the Baltic Sea, while in the 2009 study, ticks were reported for the first time from many locations in North Sweden. This included locations as far north as 66°N and places in the interior part of North Sweden. During this 16-year period the tick's range in Sweden was estimated to have increased by 9.9%. Most of the range expansion occurred in North Sweden (north of 60°N) where the tick's coverage area doubled from 12.5% in the early 1990s to 26.8% in 2008. Moreover, according to the respondents, the abundance of ticks had increased markedly in LB- and TBE-endemic areas in South (Götaland) and Central Sweden.</p> <p>Conclusions</p> <p>The results suggest that <it>I. ricinus </it>has expanded its range in North Sweden and has become distinctly more abundant in Central and South Sweden during the last three decades. However, in the northern mountain region <it>I. ricinus </it>is still absent. The increased abundance of the tick can be explained by two main factors: First, the high availability of large numbers of important tick maintenance hosts, i.e., cervids, particularly roe deer (<it>Capreolus capreolus</it>) during the last three decades. Second, a warmer climate with milder winters and a prolonged growing season that permits greater survival and proliferation over a larger geographical area of both the tick itself and deer. High reproductive potential of roe deer, high tick infestation rate and the tendency of roe deer to disperse great distances may explain the range expansion of <it>I. ricinus </it>and particularly the appearance of new TBEV foci far away from old TBEV-endemic localities. The geographical presence of LB in Sweden corresponds to the distribution of <it>I. ricinus</it>. Thus, LB is now an emerging disease risk in many parts of North Sweden. Unless countermeasures are undertaken to keep the deer populations, particularly <it>C. capreolus </it>and <it>Dama dama</it>, at the relatively low levels that prevailed before the late 1970s - especially in and around urban areas where human population density is high - by e.g. reduced hunting of red fox (<it>Vulpes vulpes</it>) and lynx (<it>Lynx lynx</it>), the incidences of human LB and TBE are expected to continue to be high or even to increase in Sweden in coming decades.</p

Evaluation of selected South African ethnomedicinal plants as mosquito repellents against the Anopheles arabiensis mosquito in a rodent model

<p>Abstract</p> <p>Background</p> <p>This study was initiated to establish whether any South African ethnomedicinal plants (indigenous or exotic), that have been reported to be used traditionally to repel or kill mosquitoes, exhibit effective mosquito repellent properties.</p> <p>Methods</p> <p>Extracts of a selection of South African taxa were tested for repellency properties in an applicable mosquito feeding-probing assay using unfed female <it>Anopheles arabiensis</it>.</p> <p>Results</p> <p>Although a water extract of the roots of <it>Chenopodium opulifolium </it>was found to be 97% as effective as DEET after 2 mins, time lag studies revealed a substantial reduction in efficacy (to 30%) within two hours.</p> <p>Conclusions</p> <p>None of the plant extracts investigated exhibited residual repellencies >60% after three hours.</p

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

<p>Abstract</p> <p>Background</p> <p>There is increasing evidence for a latitudinal and altitudinal shift in the distribution range of <it>Ixodes ricinus</it>. 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 <it>I. ricinus </it>in Norway and to evaluate if any range shifts have occurred relative to historical descriptions.</p> <p>Methods</p> <p>Multiple 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 <it>I. ricinus </it>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 <it>I. ricinus</it>. To evaluate if any geographical range shift has occurred in recent decades, the present distribution was compared to historical data from 1943 and 1983.</p> <p>Results</p> <p>Tick-borne disease and/or observations of <it>I. ricinus </it>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.</p> <p>Conclusion</p> <p><it>I. ricinus </it>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.</p

Small-scale spatial variation in infection risk shapes the evolution of a Borrelia resistance gene in wild rodents

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.Spatial variation in pathogen-mediated selection is predicted to influence the evolutionary trajectory of host populations and lead to spatial variation in their immunogenetic composition. However, to date few studies have been able to directly link small-scale spatial variation in infection risk to host immune gene evolution in natural, non-human populations. Here we use a natural rodent-Borrelia system to test for associations between landscape-level spatial variation in Borrelia infection risk along replicated elevational gradients in the Swiss Alps and Toll-like receptor 2 (TLR2) evolution, a candidate gene for Borrelia resistance, across bank vole (Myodes glareolus) populations. We found that Borrelia infection risk (i.e. the product of Borrelia prevalence in questing ticks and the average tick load of voles at a sampling site) was spatially variable and significantly negatively associated with elevation. Across sampling sites, Borrelia prevalence in bank voles was significantly positively associated with Borrelia infection risk along the elevational clines. We observed a significant association between naturally occurring TLR2 polymorphisms in hosts and their Borrelia infection status. The TLR2 variant associated with a reduced likelihood of Borrelia infection was most common in rodent populations at lower elevations that face a high Borrelia infection risk, and its frequency changed in accordance with the change in Borrelia infection risk along the elevational clines. These results suggest that small-scale spatial variation in parasite-mediated selection affects the immunogenetic composition of natural host populations, providing a striking example that the microbial environment shapes the evolution of the host’s immune system in the wild.The study was financially supported by the Swiss National Science Foundation (PP00P3_128386 and PP00P3_157455), the University of Zurich Research Priority Program ‘Evolution in Action: from Genomes to Ecosystems’, the Faculty of Science of the University of Zurich, the Baugarten Stiftung, the Stiftung für wissenschaftliche Forschung an der Universität Zürich (STWF 17_027) and the Georges und Antoine Claraz-Schenkung

Landscape structure affects the prevalence and distribution of a tick-borne zoonotic pathogen

Background Landscape structure can affect pathogen prevalence and persistence with consequences for human and animal health. Few studies have examined how reservoir host species traits may interact with landscape structure to alter pathogen communities and dynamics. Using a landscape of islands and mainland sites we investigated how natural landscape fragmentation affects the prevalence and persistence of the zoonotic tick-borne pathogen complex Borrelia burgdorferi(sensu lato), which causes Lyme borreliosis. We hypothesized that the prevalence of B. burgdorferi (s.l.) would be lower on islands compared to the mainland and B. afzelii, a small mammal specialist genospecies, would be more affected by isolation than bird-associated B. garinii and B. valaisiana and the generalist B. burgdorferi (sensu stricto). Methods Questing (host-seeking) nymphal I. Ricinus ticks (n = 6567) were collected from 12 island and 6 mainland sites in 2011, 2013 and 2015 and tested for B. burgdorferi(s.l.). Deer abundance was estimated using dung transects. Results The prevalence of B. burgdorferi (s.l.) was significantly higher on the mainland (2.5%, 47/1891) compared to island sites (0.9%, 44/4673) (P &lt; 0.01). While all four genospecies of B. burgdorferi (s.l.) were detected on the mainland, bird-associated species B. garinii and B. valaisiana and the generalist genospecies B. burgdorferi(s.s.) predominated on islands. Conclusion We found that landscape structure influenced the prevalence of a zoonotic pathogen, with a lower prevalence detected among island sites compared to the mainland. This was mainly due to the significantly lower prevalence of small mammal-associated B. afzelii. Deer abundance was not related to pathogen prevalence, suggesting that the structure and dynamics of the reservoir host community underpins the observed prevalence patterns, with the higher mobility of bird hosts compared to small mammal hosts leading to a relative predominance of the bird-associated genospecies B. garinii and generalist genospecies B. burgdorferi (s.s.) on islands. In contrast, the lower prevalence of B. afzelii on islands may be due to small mammal populations there exhibiting lower densities, less immigration and stronger population fluctuations. This study suggests that landscape fragmentation can influence the prevalence of a zoonotic pathogen, dependent on the biology of the reservoir host