Abstract:ticks carry pathogens that can cause disease in both animals and humans, and there is a need to monitor the distribution and abundance of ticks and the pathogens they carry to pinpoint potential high risk areas for tick-borne disease transmission. In a joint Scandinavian study, we measured Ixodes ricinus instar abundance at 159 sites in southern Scandinavia in August-September, 2016, and collected 29,440 tick nymphs at 50 of these sites. We additionally measured abundance at 30 sites in August-September, 2017.… Show more
“…Our study region was limited to southern Scandinavia including all of Denmark, southern Norway and south-eastern Sweden (see Figs. 1 and 2 in Kjær et al 70 ). Figure 1 Individual prevalence.…”
Section: Methodsmentioning
confidence: 93%
“…The stratification of the study region, site selection and field study have all been described in previous studies 67 , 68 , 70 . For the stratification, we used Fourier processed satellite imagery of the maximum normalized difference vegetation index 71 (NDVI) and land cover data from Corine 72 (all 1 × 1 km resolution).…”
Section: Methodsmentioning
confidence: 99%
“…In the laboratory, we stored all ticks at − 80 °C until use. For a more thorough description of site selection and collection method see Kjær et al 70 .…”
Section: Methodsmentioning
confidence: 99%
“…Methods for DNA extraction and pathogen screening have been thoroughly described elsewhere 4 , 28 , 69 , but a short description follows. We aggregated tick nymphs into pools of 10, washed and homogenized them, and then isolated genomic DNA using the Maxwell 16 LEV Blood DNA kit (Promega, Madison, Wisconsin, USA) on a Maxwell16 Instrument.…”
Section: Laboratory Methodsmentioning
confidence: 99%
“…Here we present data on prevalence for 15 different tick-borne pathogens in southern Scandinavia. The data stems from the first coordinated multi-country study in northern Europe to date, with 29,440 tick nymphs collected from 50 sites in Denmark, Norway and Sweden and are available from the figshare repository 69 . We also present predictive maps of pathogen prevalence within southern Scandinavia, developed using ML algorithms and environmental variables.…”
Tick-borne pathogens cause diseases in animals and humans, and tick-borne disease incidence is increasing in many parts of the world. There is a need to assess the distribution of tick-borne pathogens and identify potential risk areas. We collected 29,440 tick nymphs from 50 sites in Scandinavia from August to September, 2016. We tested ticks in a real-time PCR chip, screening for 19 vector-associated pathogens. We analysed spatial patterns, mapped the prevalence of each pathogen and used machine learning algorithms and environmental variables to develop predictive prevalence models. All 50 sites had a pool prevalence of at least 33% for one or more pathogens, the most prevalent being Borrelia afzelii, B. garinii, Rickettsia helvetica, Anaplasma phagocytophilum, and Neoehrlichia mikurensis. There were large differences in pathogen prevalence between sites, but we identified only limited geographical clustering. The prevalence models performed poorly, with only models for R. helvetica and N. mikurensis having moderate predictive power (normalized RMSE from 0.74–0.75, R2 from 0.43–0.48). The poor performance of the majority of our prevalence models suggest that the used environmental and climatic variables alone do not explain pathogen prevalence patterns in Scandinavia, although previously the same variables successfully predicted spatial patterns of ticks in the same area.
“…Our study region was limited to southern Scandinavia including all of Denmark, southern Norway and south-eastern Sweden (see Figs. 1 and 2 in Kjær et al 70 ). Figure 1 Individual prevalence.…”
Section: Methodsmentioning
confidence: 93%
“…The stratification of the study region, site selection and field study have all been described in previous studies 67 , 68 , 70 . For the stratification, we used Fourier processed satellite imagery of the maximum normalized difference vegetation index 71 (NDVI) and land cover data from Corine 72 (all 1 × 1 km resolution).…”
Section: Methodsmentioning
confidence: 99%
“…In the laboratory, we stored all ticks at − 80 °C until use. For a more thorough description of site selection and collection method see Kjær et al 70 .…”
Section: Methodsmentioning
confidence: 99%
“…Methods for DNA extraction and pathogen screening have been thoroughly described elsewhere 4 , 28 , 69 , but a short description follows. We aggregated tick nymphs into pools of 10, washed and homogenized them, and then isolated genomic DNA using the Maxwell 16 LEV Blood DNA kit (Promega, Madison, Wisconsin, USA) on a Maxwell16 Instrument.…”
Section: Laboratory Methodsmentioning
confidence: 99%
“…Here we present data on prevalence for 15 different tick-borne pathogens in southern Scandinavia. The data stems from the first coordinated multi-country study in northern Europe to date, with 29,440 tick nymphs collected from 50 sites in Denmark, Norway and Sweden and are available from the figshare repository 69 . We also present predictive maps of pathogen prevalence within southern Scandinavia, developed using ML algorithms and environmental variables.…”
Tick-borne pathogens cause diseases in animals and humans, and tick-borne disease incidence is increasing in many parts of the world. There is a need to assess the distribution of tick-borne pathogens and identify potential risk areas. We collected 29,440 tick nymphs from 50 sites in Scandinavia from August to September, 2016. We tested ticks in a real-time PCR chip, screening for 19 vector-associated pathogens. We analysed spatial patterns, mapped the prevalence of each pathogen and used machine learning algorithms and environmental variables to develop predictive prevalence models. All 50 sites had a pool prevalence of at least 33% for one or more pathogens, the most prevalent being Borrelia afzelii, B. garinii, Rickettsia helvetica, Anaplasma phagocytophilum, and Neoehrlichia mikurensis. There were large differences in pathogen prevalence between sites, but we identified only limited geographical clustering. The prevalence models performed poorly, with only models for R. helvetica and N. mikurensis having moderate predictive power (normalized RMSE from 0.74–0.75, R2 from 0.43–0.48). The poor performance of the majority of our prevalence models suggest that the used environmental and climatic variables alone do not explain pathogen prevalence patterns in Scandinavia, although previously the same variables successfully predicted spatial patterns of ticks in the same area.
Hard ticks (Acari: Ixodidae) act as important vectors of zoonotic pathogens. For instance, Borrelia burgdorferi s.l. spirochetes pose a severe health risk as aetiological agents of Lyme borreliosis. Commonly, to study the abundance of questing (host-seeking) ticks, a 1 m2 piece of cloth is dragged over vegetation for a determined distance. Here, we designed a tick-sampling study to estimate the sampling efficiency of this standard method. We established 10 m dragging transects in a hemiboreal mixed forest patch in SW Finland for a 5-day monitoring period. Five of the transects were cloth-dragged 3× a day, whereas another five transects were dragged 6× a day in a manner that after each morning, midday and afternoon dragging, a second dragging was conducted on the same transect immediately. Captured Ixodes ricinus ticks were subsequently analysed for tick-borne pathogens. The initial population size of nymphal ticks on a transect was approximated by the accumulated nymph catch from the dragging sessions. The sampling efficiency of the cloth dragging was low, as a single dragging in a previously untouched vegetation strip always caught less than 12% (mean 6%) of the estimated population of active nymphs that were assumed to be questing during the study. Clear results were not found for daily activity rhythm, as ticks were caught in all daily dragging sessions. Approximately every third nymph and every second adult carried a pathogen, but nothing indicated that the occurrence of a pathogen affected the likelihood of the tick being caught by cloth dragging. Our results suggest that only a minority of active ticks can be caught by a single cloth dragging. The abundance estimates in many tick investigations might thus be downward biased.
Background
The distributions of ticks and tick-borne pathogens are thought to have changed rapidly over the last two decades, with their ranges expanding into new regions. This expansion has been driven by a range of environmental and socio-economic factors, including climate change. Spatial modelling is being increasingly used to track the current and future distributions of ticks and tick-borne pathogens and to assess the associated disease risk. However, such analysis is dependent on high-resolution occurrence data for each species. To facilitate such analysis, in this review we have compiled georeferenced tick locations in the Western Palearctic, with a resolution accuracy under 10 km, that were reported between 2015 and 2021
Methods
The PubMed and Web of Science databases were searched for peer-reviewed papers documenting the distribution of ticks that were published between 2015 and 2021, using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The papers were then screened and excluded in accordance with the PRISMA flow chart. Coordinate-referenced tick locations along with information on identification and collection methods were extracted from each eligible publication. Spatial analysis was conducted using R software (version 4.1.2).
Results
From the 1491 papers identified during the initial search, 124 met the inclusion criteria, and from these, 2267 coordinate-referenced tick records from 33 tick species were included in the final dataset. Over 30% of articles did not record the tick location adequately to meet inclusion criteria, only providing a location name or general location. Among the tick records, Ixodes ricinus had the highest representation (55%), followed by Dermacentor reticulatus (22.1%) and Ixodes frontalis (4.8%). The majority of ticks were collected from vegetation, with only 19.1% collected from hosts.
Conclusions
The data presented provides a collection of recent high-resolution, coordinate-referenced tick locations for use in spatial analyses, which in turn can be used in combination with previously collated datasets to analyse the changes in tick distribution and research in the Western Palearctic. In the future it is recommended that, where data privacy rules allow, high-resolution methods are routinely used by researchers to geolocate tick samples and ensure their work can be used to its full potential.
Graphical Abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
