Temporal patterns in Ixodes ricinus microbial communities: an insight into tick-borne microbe interactions.

BACKGROUND: Ticks transmit pathogens of medical and veterinary importance and are an increasing threat to human and animal health. Assessing disease risk and developing new control strategies requires identifying members of the tick-borne microbiota as well as their temporal dynamics and interactions. METHODS: Using high-throughput sequencing, we studied the Ixodes ricinus microbiota and its temporal dynamics. 371 nymphs were monthly collected during three consecutive years in a peri-urban forest. After a Poisson lognormal model was adjusted to our data set, a principal component analysis, sparse network reconstruction, and differential analysis allowed us to assess seasonal and monthly variability of I. ricinus microbiota and interactions within this community. RESULTS: Around 75% of the detected sequences belonged to five genera known to be maternally inherited bacteria in arthropods and to potentially circulate in ticks: Candidatus Midichloria, Rickettsia, Spiroplasma, Arsenophonus and Wolbachia. The structure of the I. ricinus microbiota varied over time with interannual recurrence and seemed to be mainly driven by OTUs commonly found in the environment. Total network analysis revealed a majority of positive partial correlations. We identified strong relationships between OTUs belonging to Wolbachia and Arsenophonus, evidence for the presence of the parasitoid wasp Ixodiphagus hookeri in ticks. Other associations were observed between the tick symbiont Candidatus Midichloria and pathogens belonging to Rickettsia. Finally, more specific network analyses were performed on TBP-infected samples and suggested that the presence of pathogens belonging to the genera Borrelia, Anaplasma and Rickettsia may disrupt microbial interactions in I. ricinus. CONCLUSIONS: We identified the I. ricinus microbiota and documented marked shifts in tick microbiota dynamics over time. Statistically, we showed strong relationships between the presence of specific pathogens and the structure of the I. ricinus microbiota. We detected close links between some tick symbionts and the potential presence of either pathogenic Rickettsia or a parasitoid in ticks. These new findings pave the way for the development of new strategies for the control of ticks and tick-borne diseases. Video abstract.

Endosymbionts carried by ticks feeding on dogs in Spain.

Studies on tick microbial communities historically focused on tick-borne pathogens. However, there is an increasing interest in capturing relationships among non-pathogenic endosymbionts and exploring their relevance for tick biology. The present study included a total of 1600 adult ticks collected from domestic dogs in 4 different biogeographical regions of Spain. Each pool formed by 1 to 10 halves of individuals representing one specific ticks species was examined by PCR for the presence of Coxiellaceae, Rickettsia spp., Rickettsiales, Wolbachia spp., and other bacterial DNA. Of the pools analyzed, 92% tested positive for endosymbiont-derived DNA. Coxiella spp. endosymbionts were the most prevalent microorganisms, being always present in Rhipicephalus sanguineus sensu lato (s.l.) pools. Rickettsia spp. DNA was detected in 60% of Dermacentor reticulatus pools and 40% of R. sanguineus s.l. pools, with a higher diversity of Rickettsia species in R. sanguineus s.l. pools. Our study reveals a negative relationship of Rickettsia massiliae with the presence of tick-borne pathogens in the same pool of ticks. An additional endosymbiont, 'Candidatus Rickettsiella isopodorum', was only detected in D. reticulatus pools. Data from this study indicate that dogs in Spain are exposed to several endosymbionts. Due to the importance of tick-borne pathogens, characterizing the role of endosymbionts for tick physiology and prevalence, may lead to novel control strategies.

Biotic and abiotic factors shape the microbiota of wild-caught populations of the arbovirus vector Culicoides imicola.

Biting midges of the genus Culicoides are known vectors of arboviruses affecting human and animal health. However, little is known about Culicoides imicola microbiota and its influence on this insect's biology. In this study, the impact of biotic and abiotic factors on C. imicola microbiota was characterized using shotgun-metagenomic sequencing of whole-body DNA samples. Wild-caught C. imicola adult nulliparous females were sampled in two locations from Sicily, Italy. The climatic variables of temperature and soil moisture from both localities were recorded together with potential host bloodmeal sources. Shared core microbiome among C. imicola populations included Pseudomonas, Escherichia, Halomonas, Candidatus Zinderia, Propionibacterium, and Schizosaccharomyces. Specific and unique taxa were also found in C. imicola from each location, highlighting similarities and differences in microbiome composition between the two populations. DNA and protein identification showed differences in host preferences between the two populations, with Homo sapiens and Canis lupus familiaris L. being the preferred bloodmeal source in both locations. A principal component analysis showed that the combined effect of host preferences (H. sapiens) and local soil moisture factors shape the microbiome composition of wild-caught populations of C. imicola. These results contribute to characterizing the role of the microbiome in insect adaptation and its utility in predicting geographic expansion of Culicoides species with potential implications for the control of vector-borne diseases.

Using multi-criteria risk ranking methodology to select case studies for a generic risk assessment framework for exotic disease incursion and spread through Europe.

We present a novel approach of using the multi-criteria pathogen prioritisation methodology as a basis for selecting the most appropriate case studies for a generic risk assessment framework. The approach uses selective criteria to rank exotic animal health pathogens according to the likelihood of introduction and the impact of an outbreak if it occurred in the European Union (EU). Pathogens were evaluated based on their impact on production at the EU level and international trade. A subsequent analysis included criteria of relevance to quantitative risk assessment case study selection, such as the availability of data for parameterisation, the need for further research and the desire for the case studies to cover different routes of transmission. The framework demonstrated is flexible with the ability to adjust both the criteria and their weightings to the user's requirements. A web based tool has been developed using the RStudio shiny apps software, to facilitate this.

Redescription of the adult stages of Ixodes (Afrixodes) rasus Neumann 1899, with notes on its phylogenetic position within the genus Ixodes.

The tick subgenus Afrixodes Morel 1966 (Ixodidae) is distributed in sub-Saharan Africa. It consists of about 60 species which are described based on a few specimens and/or only some developmental stages, mostly adults. Because of this, the diagnosis of the African species of Ixodes is in many aspects complicated. Ixodes rasus Neumann 1899 is a common species, widely distributed in tropical and subtropical moist broadleaved forests in central Africa, whose morphology remains poorly described. We redescribe the adults of the species and provide molecular data for 16S rDNA based on three questing females and one male collected in the Central African Republic. Both sexes have an anal groove rounded and closed. The female has syncoxae on coxae I to III, a dental formula of 2/2, and long, curved auriculae. The male has moderate syncoxae on coxae I-III, coxae I-II carry one single internal spur each: coxae III and IV unarmed. The cornua are absent in the male, and the auriculae are small lobes. The male pregenital plate is longer than broad, with an anterior margin widely rounded; the median plate is large and clearly divergent posteriorly, with adanal plates fused posteriorly to the anus, and a dental formula of 4/4 (one row of 5/5). The molecular features of 16S rDNA place I. rasus near I. aulacodi (the only other Afrixodes species for which 16S rDNA is available) and near I. turdus and I. frontalis; two species of ticks of the Palearctic region, which commonly infest birds. The paucity of data regarding the subgenus Afrixodes makes it necessary to provide reliable and comparable re-descriptions of several species, as well as description of the immature stages for many of the currently known taxa.

A comparative test of ixodid tick identification by a network of European researchers.

This study reports the results of a comparative test of identification of ticks occurring in Western Europe and Northern Africa. A total of 14 laboratories were voluntarily enrolled in the test. Each participant received between 22 and 25 specimens of adult and nymphal ticks of 11 species: Dermacentor marginatus, D. reticulatus, Haemaphysalis punctata, Hyalomma lusitanicum, Hy. marginatum, Ixodes ricinus, I. hexagonus, Rhipicephalus annulatus, R. bursa, R. rossicus, and/or R. sanguineus s.l. Ticks were morphologically identified by three of the co-authors and the identification confirmed by a fourth co-author who used molecular methods based on several genes. Then ticks were randomly selected and blindly distributed among participants, together with a questionnaire. Only specimens collected while questing and, if possible, in the same survey, were circulated. Because of the random nature of the test, a participant could receive several specimens of the same species. Species in the different genera had variable misidentification rates (MR) of 7% (Dermacentor), 14% (Ixodes), 19% (Haemaphysalis), 36% (Hyalomma), and 54% (Rhipicephalus). Within genera, the MR was also variable ranging from 5.4% for I. ricinus or 7.4% for D. marginatus or D. reticulatus to 100% for R. rossicus. The test provided a total misidentification rate of 29.6% of the species of ticks. There are no significant differences in MR according to the sex of the tick. Participants were requested to perform a second round of identifications on the same set of ticks, using only purposely prepared keys (without illustrations), circulated to the enrolled participants, including 2 species of the genus Dermacentor, 8 of Haemaphysalis, 10 of Hyalomma, 23 of Ixodes, and 6 of Rhipicephalus. The average MR in the second round was 28%: 0% (Dermacentor), 33% (Haemaphysalis), 30% (Hyalomma) 18% (Ixodes), and 50% (Rhipicephalus). Species which are not reported in the countries of a participating laboratory had always highest MR, i.e. purely Mediterranean species had highest MR by laboratories in Central and Northern Europe. Participants expressed their concerns about a correct identification for almost 50% of the ticks of the genera Hyalomma and Rhipicephalus. The results revealed less than total confidence in identifying the most prominent species of ticks in the Western Palearctic, and underpin the need for reference libraries for specialists involved in this task. Results also showed that a combination of certain genes may adequately identify the target species of ticks.

The diversity-disease relationship: evidence for and criticisms of the dilution effect.

The dilution effect, that high host species diversity can reduce disease risk, has attracted much attention in the context of global biodiversity decline and increasing disease emergence. Recent studies have criticized the generality of the dilution effect and argued that it only occurs under certain circumstances. Nevertheless, evidence for the existence of a dilution effect was reported in about 80% of the studies that addressed the diversity-disease relationship, and a recent meta-analysis found that the dilution effect is widespread. We here review supporting and critical studies, point out the causes underlying the current disputes. The dilution is expected to be strong when the competent host species tend to remain when species diversity declines, characterized as a negative relationship between species' reservoir competence and local extinction risk. We here conclude that most studies support a negative competence-extinction relationship. We then synthesize the current knowledge on how the diversity-disease relationship can be modified by particular species in community, by the scales of analyses, and by the disease risk measures. We also highlight the complex role of habitat fragmentation in the diversity-disease relationship from epidemiological, evolutionary and ecological perspectives, and construct a synthetic framework integrating these three perspectives. We suggest that future studies should test the diversity-disease relationship across different scales and consider the multiple effects of landscape fragmentation.

Modelling the Phenological Relationships of Questing Immature Ixodes Ricinus (Ixodidae) Using Temperature and NDVI Data.

All active stages of the tick Ixodes ricinus were collected monthly at two sites in northern Spain between the years 2000 and 2007. We used percentile accumulation of the active stage in the environment to evaluate simple and coherent correlations between accumulation of the active stages of larvae and nymphs and medium-resolution MODIS satellite-derived information on the climate, including monthly and accumulated temperature and the Normalized Difference Vegetation Index (NDVI). This framework is not intended to predict the actual abundance of ticks in the field as a measure of the hazard to humans, but to provide a basic structure for addressing the phenology of the tick in its geographic range. We demonstrated that the accumulation of larval ticks in the active stage is a sigmoid function of the accumulated temperature from the beginning of the calendar year. We also demonstrated that the accumulated temperature necessary to recruit nymphs from the questing larval stage is a function of the changes in accumulated larvae and nymphs and the accumulated temperature and NDVI recorded by the Aqua sensor. The low p-values obtained in the regressions confirmed that such recruitment can be calculated using time intervals to estimate, for example, the beginning of the questing period or the time of the year when a population peak can be expected. The comparison among predicted and actual accumulated temperatures between larvae and nymph recruitment had an averaged error of ±20 days in one complete year. The use of accumulated temperature and NDVI proposed in this study opens up the re-evaluation of reports on the phenology of the tick in Europe. This framework is intended to evaluate the same correlations along the tick's range and predict its phenological patterns in areas of pathogen transmission risk for humans.

Ticks as vectors: taxonomy, biology and ecology.

Ticks are prominent parasites and competent vectors of pathogens that affect both humans and animals. This review outlines and illustrates the main features of the morphology of ticks of the families Ixodidae and Argasidae, and summarises the basic components of their life cycles. It focuses mainly on development processes and mortality among tick populations so as to provide an overview of how they are regulated in nature and how pathogens can be transmitted under such a framework. The effects of the weather on these life cycles are reviewed. The author also examines how landscape structure and biotic factors, such as the presence and abundance of hosts, may shape the density of tick populations. The uncertainty inherent in dealing with the transmission of pathogens by ticks is highlighted; this results from the sometimes complex relationships among the vectors, the climate and the presence and density of host populations. The need to obtain reliable field estimations of such relationships before drawing conclusions about the effects of the isolated components of the system is stressed. A section is devoted to addressing the expected (and not yet totally understood) effects of trends in climate on the spread of ticks, and how these can be analysed and tracked.

Methodological caveats in the environmental modelling and projections of climate niche for ticks, with examples for Ixodes ricinus (Ixodidae).

Interest is increasing in inferring the climate niche of health-threatening arthropods and projecting such inferences onto a territory. This approach is intended to predict the range of tick distribution and to elucidate tick responses to climate scenarios, using so-called correlative models. However, some methodological gaps might prevent achieving an adequate background for hypothesis testing. We explore, describe, and illustrate these procedural inaccuracies with examples focused on the tick Ixodes ricinus and examine how these factors might affect modelling outcomes. Our aim was to develop a backdrop of rules for developing reliable models for these parasites. The use of partial sets of tick occurrences might produce unreliable associations with climate because the algorithms cannot capture the complete niche with which the tick is associated. Reliability measures of the model cannot detect these inaccuracies, and undesirable estimations of the niche will prevail in the chain of further calculations. The use of inadequate environmental variables (covariates) may lead to inflation of the results of the model through two statistical processes, autocorrelation and colinearity. We demonstrate the high colinearity existing in climate products derived from interpolation of climate recording stations. Our explicit advice is to focus on the training of climate models with satellite-derived information of climate, from which colinearity of the time series has been removed through a harmonic regression. We also emphasize the high uncertainty if inference about the climate niche is expanded into different time slices, like projected climate scenarios.

Species distribution modelling for Rhipicephalus microplus (Acari: Ixodidae) in Benin, West Africa: comparing datasets and modelling algorithms.

Rhipicephalus microplus is one of the most widely distributed and economically important ticks, transmitting Babesia bigemina, B. bovis and Anaplasma marginale. It was recently introduced to West Africa on live animals originating from Brazil. Knowing the precise environmental suitability for the tick would allow veterinary health officials to draft vector control strategies for different regions of the country. To test the performance of modelling algorithms and different sets of environmental explanatory variables, species distribution models for this tick species in Benin were developed using generalized linear models, linear discriminant analysis and random forests. The training data for these models were a dataset containing reported absence or presence in 104 farms, randomly selected across Benin. These farms were sampled at the end of the rainy season, which corresponds with an annual peak in tick abundance. Two environmental datasets for the country of Benin were compared: one based on interpolated climate data (WorldClim) and one based on remotely sensed images (MODIS). The pixel size for both environmental datasets was 1 km. Highly suitable areas occurred mainly along the warmer and humid coast extending northwards to central Benin. The northern hot and drier areas were found to be unsuitable. The models developed and tested on data from the entire country were generally found to perform well, having an AUC value greater than 0.92. Although statistically significant, only small differences in accuracy measures were found between the modelling algorithms, or between the environmental datasets. The resulting risk maps differed nonetheless. Models based on interpolated climate suggested gradual variations in habitat suitability, while those based on remotely sensed data indicated a sharper contrast between suitable and unsuitable areas, and a patchy distribution of the suitable areas. Remotely sensed data yielded more spatial detail in the predictions. When computing accuracy measures on a subset of data along the invasion front, the modelling technique Random Forest outperformed the other modelling approaches, and results with MODIS-derived variables were better than those using WorldClim data. The high environmental suitability for R. microplus in the southern half of Benin raises concern at the regional level for animal health, including its potential to substantially alter transmission risk of Babesia bovis. The northern part of Benin appeared overall of low environmental suitability. Continuous surveillance in the transition zone however remains relevant, in relation to important cattle movements in the region, and to the invasive character of R. microplus.

Assessing the statistical relationships among water-derived climate variables, rainfall, and remotely sensed features of vegetation: implications for evaluating the habitat of ticks.

Ticks are sensitive to changes in relative humidity and saturation deficit at the microclimate scale. Trends and changes in rainfall are commonly used as descriptors of field observations of tick populations, to capture the climate niche of ticks or to predict the climate suitability for ticks under future climate scenarios. We evaluated daily and monthly relationships between rainfall, relative humidity and saturation deficit over different ecosystems in Europe using daily climate values from 177 stations over a period of 10 years. We demonstrate that rainfall is poorly correlated with both relative humidity and saturation deficit in any of the ecological domains studied. We conclude that the amount of rainfall recorded in 1 day does not correlate with the values of humidity or saturation deficit recorded 24 h later: rainfall is not an adequate surrogate for evaluating the physiological processes of ticks at regional scales. We compared the Normalized Difference Vegetation Index (NDVI), a descriptor of photosynthetic activity, at a spatial resolution of 0.05°, with monthly averages of relative humidity and saturation deficit and also determined a lack of significant correlation. With the limitations of spatial scale and habitat coverage of this study, we suggest that the rainfall or NDVI cannot replace relative humidity or saturation deficit as descriptors of tick processes.

Deconstructing Ixodes ricinus: a partial matrix model allowing mapping of tick development, mortality and activity rates.

A stage-structured Leslie matrix model of a partial, discrete population of Ixodes ricinus (Linnaeus) (Ixodida: Ixodidae) ticks was developed to elucidate the impact of climate trends on the distribution and phenology of this species in the western Palaearctic. The model calculates development and mortality rates for each instar and evaluates recruitment rates based on the development of the tick population. The model captures the changes in development and mortality rates, providing a coherent index of performance correlated with the tick's geographic range. Maximum development rates are recorded for latitudes south of 36 °N and are spatially correlated with sites of maximum temperature, highest saturation deficit and highest mortality. The maximum available developmental time (the total annual time during which temperature allows development) for I. ricinus in the western Palaearctic is < 45% of the total year. North of 60 °N, available developmental time decreases sharply to only 15% of the year. The latitudinal boundary at which survival rates sharply drop is 43-46 °N, clearly delimiting the classically recognized extent of the main tick populations. The pattern of activity for larval-nymphal synchrony shows a clear west-east pattern. The model demonstrates the impact of climate according to tick stage and geographic location, and provides a practical framework for testing how the tick's lifecycle is affected by climate change.

Factors driving the circulation and possible expansion of Crimean-Congo haemorrhagic fever virus in the western Palearctic.

AIMS: To produce a spatial risk map regarding spread of Crimean-Congo haemorrhagic fever virus (CCHFV) in the western Palearctic by linking a process-driven model of the main tick vector, Hyalomma marginatum, to a Next Generation Matrix. METHODS AND RESULTS: Process-driven model was composed of deterministic equations that simulate developmental and mortality rates of different tick stages by using temperature and atmospheric water vapour data. The model used climate data at 10-day intervals at a spatial resolution of 10 min over western Palearctic. The model estimated the basic reproduction number, R0, for CCHFV transmission by H. marginatum ticks and evaluated how changes in temperature and biological parameters may alter the geographical range of CCHFV. In particular, variation in the rate of transovarial transmission of CCHFV in the tick produced the greatest change in CCHFV circulation in the tick population. Parameters affecting the rates of tick bite, non-systemic transmission and efficiency of tick-to-tick transmission had little effect on R0. Temperature changes that affect tick development, survival and activity rates increased the suitable area for CCHFV transmission at higher latitudes in the western Palearctic. CONCLUSIONS: Non-systemic transmission had little impact on virus transmission under all scenarios. In the area studied, increase of temperature has no impact on the routes of transmission of CCHFV. However, climate conditions favouring tick survival, which increase infected adult tick populations, together with large numbers of hosts for adults were predicted as the most likely scenario for the spread of the virus in the studied area. SIGNIFICANCE AND IMPACT OF THE STUDY: The proposed framework is able to capture the dynamics and the relative contribution of the different routes (hosts, ticks) in the transmission and spread of an important pathogen affecting human health. The high contribution of the transovarial transmission route makes the process highly dependent upon suitable hosts for adult ticks, like large domestic and wild ungulates. Climate seems to have a very reduced effect on such spread.

Association of environmental traits with the geographic ranges of ticks (Acari: Ixodidae) of medical and veterinary importance in the western Palearctic. A digital data set.

We compiled information on the distribution of ticks in the western Palearctic (11°W, 45°E; 29°N, 71°N), published during 1970-2010. The literature search was filtered by the tick's species name and an unambiguous reference to the point of capture. Records from some curated collections were included. We focused on tick species of importance to human and animal health, in particular: Ixodes ricinus, Dermacentor marginatus, D. reticulatus, Haemaphysalis punctata, H. sulcata, Hyalomma marginatum, Hy. lusitanicum, Rhipicephalus annulatus, R. bursa, and the R. sanguineus group. A few records of other species (I. canisuga, I. hexagonus, Hy. impeltatum, Hy. anatolicum, Hy. excavatum, Hy. scupense) were also included. A total of 10,280 records was included in the data set. Almost 42 % of published references are not adequately referenced (and not included in the data set), host is reported for only 61 % of records and a reference to time of collection is missed for 84 % of published records. Ixodes ricinus accounted for 44.3 % of total records, with H. marginatum and D. marginatus accounting for 7.1 and 8.1 % of records, respectively. The lack of homogeneity of the references and potential pitfalls in the compilation were addressed to create a digital data set of the records of the ticks. We attached to every record a coherent set of quantitative descriptors for the site of reporting, namely gridded interpolated monthly climate and remotely sensed data on vegetation (NDVI). We also attached categorical descriptors of the habitat: a standard classification of land biomes and an ad hoc classification of the target territory from remotely sensed temperature and NDVI data. A descriptive analysis of the data revealed that a principal components reduction of the environmental (temperature and NDVI) variables described the distribution of the species in the target territory. However, categorical descriptors of the habitat were less effective. We stressed the importance of building reliable collections of ticks with specific references as to collection point, host and date of capture. The data set is freely downloadable.

Vector-borne pathogen spread through ticks on migratory birds: a probabilistic spatial risk model for South-Western europe.

Tick-borne pathogens can spread easily through the movements of infested birds. An important example is viruses that pose a threat to humans and that are carried in Hyalomma ticks that move from Africa into south-western Europe. This study evaluates the probability of arrival of migrating birds from Africa into Spain and the environmental suitability of different regions of Spain for the survival of tick stages introduced by these birds. This evaluation produced a spatial risk index measuring the probability that foreign tick populations will survive in the target area. Periods of highest risk were observed for large areas of Spain, from the second fortnight of April to the second fortnight of May. Although birds may arrive as early as January and massive migrations may take place in March, the environmental suitability for Hyalomma marginatum ticks is low in these periods and high mortality of the spread stages (nymphs) is expected. This study introduces new methods of objective analysis based on spatial and process-driven models for both ticks and hosts and critically evaluates the usefulness of spatial spreading methods for assessing the risk of tick-borne pathogens.

Subolesin/Akirin vaccines for the control of arthropod vectors and vectorborne pathogens.

Diseases transmitted by arthropod vectors such as mosquitoes, ticks and sand flies greatly impact human and animal health, and therefore, their control is important for the eradication of vectorborne diseases (VBD). Vaccination is an environmentally friendly alternative for vector control that allows control of several VBD by targeting their common vector. Recent results have suggested that subolesin (SUB) and its orthologue in insects, akirin (AKR) are good candidate antigens for the control of arthropod vector infestations and pathogen infection. SUB was discovered as a tick-protective antigen in Ixodes scapularis. Vaccination trials with recombinant SUB/AKR demonstrated effective control of arthropod vector infestations in various hard and soft tick species, mosquitoes, sand flies, poultry red mites and sea lice by reducing their numbers, weight, oviposition, fertility and/or moulting. SUB/AKR vaccination also reduced tick infection with tickborne pathogens, Anaplasma phagocytophilum, A. marginale, Babesia bigemina and Borrelia burgdorferi. The effect of vaccination on different hosts, vector species, developmental stages and vectorborne pathogen infections demonstrated the feasibility of SUB/AKR universal vaccines for the control of multiple vector infestations and for reduction in VBD.

A population model to describe the distribution and seasonal dynamics of the tick Hyalomma marginatum in the Mediterranean Basin.

A dynamic population model of Hyalomma marginatum, the vector of several pathogens in the western Palearctic, was developed to simulate effects of temperature and water vapour deficit (VD) on tick survival, development rates and seasonality. Base tick survival and development rates were obtained from laboratory-controlled experiments or calculated from reported data. These rates were modelled as temperature-dependant time delays or accumulated mortality by temperature and water VD stress. Using daily data derived from a gridded data set at 10-min resolution, the model reached stable and cyclical equilibria in an area that corresponds largely with the reported distribution of the tick in western Palearctic. The model did not identify a potential range of suitable climate for the tick out of the known distribution area, implying that under current climate conditions, there is no potential to spread at the spatial scale of the model. Tick die-out at northern latitudes was attributed to a steady increase in duration of the development rates of engorged nymphs to adults and hence increased mortality in this stage. Low developmental rates in northern latitudes produced the accumulation of most of the nymphal stock in late summer and early autumn, which cannot moult to adults because of the low temperatures of late autumn and winter. The tick did not produced self-sustained populations in areas where yearly accumulated temperatures were below 3000-4000 °C, a limit roughly found at latitudes north of 47 ºN. Tick die-out in sites southern to 34 ºN was attributed to the mortality rates of engorged nymphs, which moult in late spring and summer, in the season where temperatures and water vapour stresses were highest. These findings and future applications of the model in investigating the dynamics of pathogens potentially transmitted by H. marginatum are discussed.

The trend towards habitat fragmentation is the key factor driving the spread of Crimean-Congo haemorrhagic fever.

We aimed to characterize an environmental niche driving the distribution of Crimean-Congo haemorrhagic fever (CCHF) in Turkey, using a geo-referenced collection of cases reported between 2003 and 2008 and a set of climate and vegetation features. We used mean monthly air temperatures and Normalized Derived Vegetation Index (NDVI) values, at a resolution of 0.1 degrees , as well as climate features at and below the surface. We computed significant differences in monthly variables between positive and negative sites, within the range of distribution of the tick vector. Seasonal climate (growth season and summer length, accumulated temperatures in winter) and vegetation components (anomalies in NDVI data) were analysed. Fragmentation of habitat was obtained from NDVI monthly data at a resolution of 1 km. Neither single climate or vegetation variables, nor any individual seasonal component, accounted in both space and time for the delineation of areas of disease although accumulated temperatures in winter consistently showed lower values in areas where the disease was reported. Coherent and significant differences between disease-containing and disease-free sites were found when habitat fragmentation and connectivity were examined. High fragmentation and connectivity were unambiguously associated with sites where disease is reported and accounted for the spatial spread of cases in 2003-2008. CCHF cases were always associated with areas of highly fragmented and well-connected patches within the range of the tick vector, while there were no reports from areas with low fragmentation. There was a linear relationship between degree of fragmentation and case incidence. The implications of these findings are discussed with reference to the concept of disease spread through networks of connected spots with high densities of infected vectors and social factors driving different human activities in sites of high fragmentation.

The feasibility of developing a risk assessment for the impact of climate change on the emergence of Crimean-Congo haemorrhagic fever in livestock in Europe: a review.

Crimean-Congo haemorrhagic fever virus (CCHFV) is one of the most widespread of all medically important arboviruses with ticks of the Hyalomma spp. serving as the main vectors. Infection of livestock by CCHFV serves as a route of exposure to humans, as a reservoir of disease and as a route of importation. This study discusses the pathways and data requirements for a qualitative risk assessment for the emergence of CCHFV in livestock in Europe. A risk map approach is proposed based on layers that include the potential routes of release (e.g. by migrating birds carrying infected ticks) together with the main components for exposure, namely the distributions of the tick vectors, the small vertebrate host reservoirs and the livestock. A layer on landscape fragmentation serves as a surrogate for proximity of livestock to the tick cycle. Although the impact of climate change on the emergence of CCHF is not clear, comparing the distribution of risk factors in each layer currently with those predicted in the 2080s with climate change can be used to speculate how potential high-risk areas may shift. According to the risk pathway, transstadial and/or transovarial transmission in the tick vector are crucial for CCHFV spread. Vector competence and tick vector switching, however, remain critical factors for CCHFV colonization of new regions in Europe. The species of migratory bird is also an important consideration in the release assessment with greater abundance and biodiversity of ground-dwelling birds in southern Europe than in northern Europe.