Assessing the effects of variables and background selection on the capture of the tick climate niche

Background: Modelling the environmental niche and spatial distribution of pathogen-transmitting arthropods involves various quality and methodological concerns related to using climate data to capture the environmental niche. This study tested the potential of MODIS remotely sensed and interpolated gridded covariates to estimate the climate niche of the medically important ticks Ixodes ricinus and Hyalomma marginatum. We also assessed model inflation resulting from spatial autocorrelation (SA) and collinearity (CO) of covariates used as time series of data (monthly values of variables), principal components analysis (PCA), and a discrete Fourier transformation. Performance of the models was measured using area under the curve (AUC), autocorrelation by Moran's I, and collinearity by the variance inflation factor (VIF).Results: The covariate spatial resolution slightly affected the final AUC. Consistently, models for H. marginatum performed better than models for I. ricinus, likely because of a species-derived rather than covariate effect because the former occupies a more limited niche. Monthly series of interpolated climate always better captured the climate niche of the ticks, but the SA was around 2 times higher and the maximum VIF between covariates around 30 times higher in interpolated than in MODIS-derived covariates. Interpolated or remotely sensed monthly series of covariates always had higher SA and CO than their transformations by PCA or Fourier. Regarding the effects of background point selection on AUC, we found that selection based on a set of rules for the distance to the core distribution and the heterogeneity of the landscape influenced model outcomes. The best selection relied on a random selection of points as close as possible to the target organism area of distribution, but effects are variable according to the species modelled.Conclusion: Testing for effects of SA and CO is necessary before incorporating these covariates into algorithms building a climate envelope. Results support a higher SA and CO in an interpolated climate dataset than in remotely sensed covariates. Satellite-derived information has fewer drawbacks compared to interpolated climate for modelling tick relationships with environmental niche. Removal of SA and CO by a harmonic regression seems most promising because it retains both biological and statistical meaning.Peer reviewedVeterinary Pathobiolog

Contributions to the morphology and phylogeny of the newly discovered bat tick species, Ixodes ariadnae in comparison with I. vespertilionis and I. simplex

Background: Recently a new hard tick species, Ixodes ariadnae has been discovered, adding to the two known ixodid tick species (I. vespertilionis and I. simplex) of bats in Europe. Findings: Scanning electron microscopic comparison of adult females of these species shows morphological differences concerning the palps, the scutum, the Haller's organ, the coxae, as well as the arrangement and fine structure of setae. Molecular analysis of 10 geographically different isolates revealed 90-95% sequence homology in the 12S and 16S rDNA genes of bat tick species. Based on 12S rDNA sequences, genotypes of I. ariadnae clustered closest to I. simplex, whereas according to their 16S rDNA gene they were closest to I. vespertilionis. The subolesin gene of I. ariadnae had only 91% sequence homology with that of I. ricinus, and is the longest known among hard tick species. Conclusions: The present study illustrates the morphology and clarifies the phylogenetic relationships of the three known bat tick species that occur in Europe. According to its subolesin gene I. ariadnae may have a long evolutionary history

First evidence of established populations of the taiga tick Ixodes persulcatus (Acari: Ixodidae) in Sweden

Background: The tick species Ixodes ricinus and I. persulcatus are of exceptional medical importance in the western and eastern parts, respectively, of the Palaearctic region. In Russia and Finland the range of I. persulcatus has recently increased. In Finland the first records of I. persulcatus are from 2004. The apparent expansion of its range in Finland prompted us to investigate if I. persulcatus also occurs in Sweden. Methods: Dog owners and hunters in the coastal areas of northern Sweden provided information about localities where ticks could be present. In May-August 2015 we used the cloth-dragging method in 36 localities potentially harbouring ticks in the Bothnian Bay area, province Norrbotten (NB) of northern Sweden. Further to the south in the provinces Vasterbotten (VB) and Uppland (UP) eight localities were similarly investigated. Results: Ixodes persulcatus was detected in 9 of 36 field localities in the Bothnian Bay area. Nymphs, adult males and adult females (n = 46 ticks) of I. persulcatus were present mainly in Alnus incana - Sorbus aucuparia - Picea abies - Pinus sylvestris vegetation communities on islands in the Bothnian Bay. Some of these I. persulcatus populations seem to be the most northerly populations so far recorded of this species. Dog owners asserted that their dogs became tick-infested on these islands for the first time 7-8 years ago. Moose (Alces alces), hares (Lepus timidus), domestic dogs (Canis lupus familiaris) and ground-feeding birds are the most likely carriers dispersing I. persulcatus in this area. All ticks (n = 124) from the more southern provinces of VB and UP were identified as I. ricinus. Conclusions: The geographical range of the taiga tick has recently expanded into northern Sweden. Increased information about prophylactic, anti-tick measures should be directed to people living in or visiting the coastal areas and islands of the Baltic Bay.Peer reviewe

High degree of mitochondrial gene heterogeneity in the bat tick species Ixodes vespertilionis, I. ariadnae and I. simplex from Eurasia

Background: Phylogeographical studies allow precise genetic comparison of specimens, which were collected over large geographical ranges and belong to the same or closely related animal species. These methods have also been used to compare ticks of veterinary-medical importance. However, relevant data are missing in the case of ixodid ticks of bats, despite (1) the vast geographical range of both Ixodes vespertilionis and Ixodes simplex, and (2) the considerable uncertainty in their taxonomy, which is currently unresolvable by morphological clues. Methods: In the present study 21 ticks were selected from collections or were freshly removed from bats or cave walls in six European and four Asian countries. The DNA was extracted and PCRs were performed to amplify part of the cytochrome oxidase I (COI), 16S and 12S rDNA genes, followed by sequencing for identification and molecular-phylogenetic comparison. Results: No morphological differences were observed between Ixodes vespertilionis specimens from Spain and from other parts of Europe, but corresponding genotypes had only 94.6 % COI sequence identity. An I. vespertilionis specimen collected in Vietnam was different both morphologically and genetically (i.e. with only 84.1 % COI sequence identity in comparison with I. vespertilionis from Europe). Two ticks (collected in Vietnam and in Japan) formed a monophyletic clade and shared morphological features with I. ariadnae, recently described and hitherto only reported in Europe. In addition, two Asiatic specimens of I. simplex were shown to differ markedly from European genotypes of the same species. Phylogenetic relationships of ticks showed similar clustering patterns with those of their associated bat host species. Conclusions: Although all three ixodid bat tick species evaluated in the present study appear to be widespread in Eurasia, they exhibit pronounced genetic differences. Data of this study also reflect that I. vespertilionis may represent a species complex

The biology and ecology of ticks shape the potential for the transmission of zoonotic pathogens

Ticks are noticeable by the high diversity of pathogens they can transmit, most of them with implications in human and animal health. Ticks are arachnids, meaning that they do not share the biological and ecological features of the mosquitoes and other parasitic Diptera. The natural foci of tick-borne pathogens may be as large as a continent, or be restricted to small portions of a country, without apparently too many similar features. The life cycle of the ticks involved three developing instars. The precise relationships of ticks and their hosts, the specific seasonal pattern of activity of ticks, and the still poorly known molecular relationships between ticks and the pathogens they can transmit, make these vectors a specially fecund field of research. Importantly, extensive studies on the biological and ecological relationships of ticks and abiotic (climate and vegetation) conditions have revealed the fine-tuning of the ticks and the pathogens they transmit, together with the biological effects of host and the driving features by the climate. The studies on tick-transmitted pathogens have been on the rise in the last years. There is a growing interest in understand the somewhat complex relationships between the landscape, the climate, the vectors and the pathogens, because the concerns of spread, probably driven by subtle changes in climate and man made alterations of the landscape. Studies on Lyme borreliosis are addressing the interesting issue of the relationships between the climate, the tick activity patterns, and the selection of strains according to the reservoir availability. Furthermore, the expanding field of habitat suitability modeling has been applied with different degrees of success to evaluate and quantify the risk of disease transmission. In such exponentially growing field, revisionary books are clearly welcome additions to the bibliographical tools of researchers. It is however necessary the compilation of works devoted to explore the tip of the iceberg in the field of research. In this Research Topic, we wish to summarize and review the studies on ecology, molecular biology, and tick-host-pathogens interactions, provided to resolve the important issues of ticks and pathogens. We want not only the results obtained by newly developed molecular tools, but rigorous reviews of the most recent advances in these issues. This Topic will cover aspects of both human and animal health, with special interest on zoonoses. Aspects of the biology of the ticks, as affecting the transmission of pathogens, are of special interest in this Topic. Studies on ticks of the poorly known family Argasidae, as related to their involvement on pathogen transmission, are especially welcome. We also wish to describe the perspective of the field in the future. Finally, the presentation of ongoing original works is greatly encouraged