BackgroundOne of the major public health challenges in the field of communicable diseases consists of being able to predict where and when a population is at risk of being infected by a pathogen. In the case of vector-borne diseases, such predictions often require strong ecological knowledge of the vector life-cycle and the environmental conditions promoting or preventing its establishment and maintenance. In this study, we analyse how climatic factors influence the abundance and phenology of the Lyme borreliosis vector Ixodes ricinus in a Swiss temperate forest, based on a long-term monthly observation over a period of 15 years (2000 and 2014).ResultsOur results show that questing nymph density significantly decreased during the study period in the sampling area. Although the analyses of climatic variables point out the relative importance of air temperature, relative humidity and saturation deficit on nymph questing activity, the global trends followed by these variables over the study period failed to fully explain the observed decline. However, nymph phenology was additionally explained by the presence of climatic thresholds that limit the questing behaviours of ticks. Most notably, we found that the presumed upper threshold of air saturation deficit, which strongly limits the increase of questing nymph density and is typically reached in the middle of spring, was reached significantly earlier and earlier over years.ConclusionsIn addition to phenology per se, the use of climatic thresholds may help to predict the presence and abundance of questing ticks in Lyme borreliosis endemic areas. Tick sensitivity to temperature or saturation deficit thresholds also suggests that extreme climatic events more than global trends may affect tick population dynamics. These two points may be of high importance in epidemiological short-term as well as long-term predictions. However, the highly unexplained variability in nymph density underlines the need for further studies that include other factors such as tick host abundance or tick microhabitats, two potentially influent factors that were not assessed in the present study.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-2876-7) contains supplementary material, which is available to authorized users.

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BackgroundAnthropogenic disturbances are changing the geographic distribution of ticks and tick-borne diseases. Over the last few decades, the tick Ixodes ricinus has expanded its range and abundance considerably in northern Europe. Concurrently, the incidence of tick-borne diseases, such as Lyme borreliosis and tick-borne encephalitis, has increased in the human populations of the Scandinavian countries.MethodsWildlife populations can serve as sentinels for changes in the distribution of tick-borne diseases. We used serum samples from a long-term study on the Scandinavian brown bear, Ursus arctos, and standard immunological methods to test whether exposure to Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, and tick-borne encephalitis virus (TBEV) had increased over time. Bears had been sampled over a period of 18 years (1995–2012) from a southern area, where Ixodes ricinus ticks are present, and a northern area where ticks are uncommon or absent.ResultsBears had high levels of IgG antibodies against B. burgdorferi sensu lato but not TBEV. Bears at the southern area had higher values of anti-Borrelia IgG antibodies than bears at the northern area. Over the duration of the study, the value of anti-Borrelia IgG antibodies increased in the southern area but not the northern area. Anti-Borrelia IgG antibodies increased with the age of the bear but declined in the oldest age classes.ConclusionsOur study is consistent with the view that ticks and tick-borne pathogens are expanding their abundance and prevalence in Scandinavia. Long-term serological monitoring of large mammals can provide insight into how anthropogenic disturbances are changing the distribution of ticks and tick-borne diseases.

This article aims to propose an approach for estimating the three-dimensional (3D) variability of denitrification. The concept of functional horizons is applied to the process of biological denitrification and 3D soil horizon cartography is used to estimate its spatial variation. On one hand, detailed fieldwork (186 pedological auger holes) was undertaken to map 3D horizon distribution within a 3-ha riparian area using Geographical Information Systems (GIS). On the other hand, three classes of denitrifying capacities were defined according to the distribution of the denitrifying enzyme activity of 51 samples. The relationship between the process of denitrification and the cartography is assessed through soil characteristics, which both differentiate soil horizons and control the process of denitrification: organic carbon and textural fractions. This allows a class of denitrifying capacity to be attributed to each soil horizon. This information was inserted into the 3D soil horizon cartography and the denitrifying functional horizons could be delimited. With this approach, field criteria are used and variations of the 3D distribution of