Hosts on which nymphal Ixodes ricinus most abundantly feed

Host-utilization differences between larval and nymphal deer ticks in northeastern U.S. sites enzootic for Borrelia burgdorferi sensu stricto

In the northeastern U.S., Borrelia burgdorferi sensu stricto, the agent of Lyme disease, is maintained between vertebrate hosts and subadult deer ticks (the northern clade of Ixodes scapularis, formerly known as Ixodes dammini). Theoretical arguments suggest that the force of transmission would be greatest when infected nymphal ticks focus their bites on the same host as the uninfected larvae. Stage-specific differences in host utilization would reduce the force of transmission, but to date such differences remain understudied. We determined the host utilization differences of larval and nymphal deer ticks using bloodmeal analysis of host-seeking nymphs and adults collected from 5 field sites in New England. Matched cohorts of ticks (nymphs=506, adults=451), i.e. ticks that had fed during the same summer season, were used to control for yearly host population variations. Infection status of all ticks was determined by real time PCR. Nymphal deer ticks were more likely to have fed on birds and sciurids (13% vs 3%, and 41% vs 9%, respectively p<0.001) and larvae were more likely to have fed on shrews (26% vs 3%, p<0.001). Similarly, ticks that had fed on a mouse or a shrew as larvae were likely to become infected (OR= 3.195, 95% CI [1.9, 5.1] and OR=2.5[1.6,3.8] respectively), and they were positively associated with infection prevalence at our sites. However, very few nymphs fed on shrews, and they were not associated with infection, raising the question of how uninfected shrews acquire infection each year. Sciurids did not appear to contribute to the enzootic cycle at our sites, which may be due to the low numbers of larvae that fed on them. Sciurid-fed ticks of either stage were not associated with infection. Both stages of ticks were less likely to be infected if they had fed on deer (OR=0.08 [0.02.0.3] and OR=0.4 [0.2,0.7] tested as nymphs and adults, respectively) and thus deer likely served to reduce the force of transmission at our sites. Site-specific analysis of differential host utilization by subadult deer ticks may contribute to appropriate targeting of interventions and thereby promote reducing risk of acquiring Lyme disease and the other deer tick-transmitted infections.

Voles, shrews and red squirrels as sources of tick blood meals and tick-borne pathogens on an island in southwestern Finland

Molecular identification of the previous blood meal source of a questing tick (Acari: Ixodidae) from blood meal fragments was proposed a few decades ago. Following this, several blood meal assays have been developed and published, but none of them have been taken into widespread use. Recently, novel retrotransposon-based qPCR assays designed for detecting blood meal fragments of North American host species were published. We wanted to assess their function with host species present in Finland. Questing ticks were collected by cloth dragging in August-September 2021 from an island in southwestern Finland. DNA was extracted from Ixodes ricinus nymphs (n=438) and qPCR assays applied to identify larval blood meal sources (voles, shrews and red squirrels) and screen for several tick-borne human pathogens and other microbes with pathogenic potential [Borrelia spp. (including specific assays for Borrelia afzelii, Borrelia garinii, Borrelia valaisiana), Anaplasma phagocytophilum, Babesia spp., Rickettsia spp., and Neoehrlichia mikurensis]. The probability of a nymph having fed as larva on either a vole, shrew or red squirrel was 0.34 (0.30 - 0.38; 95% confidence interval). Bacteria of the genus Borrelia were the most common pathogens detected, with host-specific probabilities of carrying Borrelia of 0.30 (0.18 - 0.44) for nymphs that had fed on voles, 0.23 (0.14 - 0.35) for nymphs that had fed on shrews, and 0.42 (0.28 - 0.58) for nymphs that had fed on red squirrels. Other microbes were rarely acquired from these hosts, apart from N. mikurensis from voles. This study highlights that shrews and red squirrels may equal voles as blood meal sources for I. ricinus larvae. Overall, variation in proportions of blood meals provided by these animals may be high across even proximate study areas. All studied host species appeared to be important sources for particularly Borrelia afzelii, and voles also for N. mikurensis.

Multi-Locus Sequencing Reveals Putative Novel Anaplasmataceae Agents, 'Candidatus Ehrlichia dumleri' and Anaplasma sp., in Ring-Tailed Coatis (Carnivora: Nasua nasua) from Urban Forested Fragments at Midwestern Brazil

The Anaplasmataceae family encompasses obligate intracellular α-proteobacteria of human and veterinary medicine importance. This study performed multi-locus sequencing to characterize Ehrlichia and Anaplasma in coati's blood samples in Midwestern Brazil. Twenty-five samples (25/165-15.1%) were positive in the screening PCR based on the dsb gene of Ehrlichia spp. and were characterized using 16S rRNA, sodB, groEL, and gltA genes and the 23S-5S intergenic space region (ITS). Phylogenetic analyses based on all six molecular markers positioned the sequences into a new clade, with a common origin of Ehrlichia ruminantium. Haplotype analyses of 16S RNA sequences revealed the presence of two distinct Ehrlichia genotypes. Six samples (6/165, 3.6%) were positive in the screening nPCR for the 16S rRNA gene of Anaplasma spp. and were submitted to an additional PCR targeting the ITS for molecular characterization. Phylogenetic analyses based on both 16S rRNA gene and ITS positioned the Anaplasma sp. detected in the present study in a large clade with other Anaplasma sp. previously detected in ticks and wild animals and in a clade with 'Candidatus Anaplasma brasiliensis', respectively. Based on distinct molecular markers, the present work described a putative novel Anaplasmataceae agent, namely 'Candidatus Ehrlichia dumleri', and Anaplasma sp. closely related to the previously described 'Candidatus Anaplasma brasiliensis'.

Ticks in the metropolitan area of Berlin, Germany

A high-resolution city map showing the geographic distribution of 12 tick species (Acari: Argasidae, Ixodidae) that have been recorded from the metropolitan area of Berlin, Germany is presented. A total of 237 tick locations was mapped. These include ten ixodid tick species: Dermacentor reticulatus, Haemaphysalis concinna, Hyalomma rufipes, Ixodes ricinus, Ixodes canisuga, Ixodes hexagonus, Ixodes arboricola, Ixodes frontalis, Ixodes trianguliceps and Rhipicephalus sanguineus sensu lato. The two tick species Hy. rufipes and R. sanguineus s.l. are not endemic to Berlin. Hyalomma rufipes ticks are introduced in Europe with migratory birds from Africa every spring. Rhipicephalus sanguineus s.l. are introduced to Central Europe with dogs that had travelled to or were imported from countries where this tick is endemic. In Germany, they are able to develop and reproduce inside heated buildings. Occurrences of two soft tick species, the pigeon tick Argas reflexus and the short-legged bat tick Carios vespertilionis were also mapped. Other tick species that are likely to be endemic to Berlin and its environs, but for which documented findings or geographical coordinates are lacking, are mentioned. These include the long-legged bat tick I. vespertilionis and the marten tick I. rugicollis documented in Brandenburg, the federal state surrounding Berlin. It can be assumed that if appropriate field studies are carried out, these tick species will also be found in the metropolitan area of Berlin. The high-resolution mapping of all tick species found in a city (like Berlin) forms the basis for further investigations into the impact of climate change and changing land use on ticks and tick-borne diseases, precisely in those habitats where most people will live in the future.

Predicting habitat suitability for Ixodes ricinus and Ixodes persulcatus ticks in Finland

Background

Ticks are responsible for transmitting several notable pathogens worldwide. Finland lies in a zone where two human-biting tick species co-occur: Ixodesricinus and Ixodespersulcatus. Tick densities have increased in boreal regions worldwide during past decades, and tick-borne pathogens have been identified as one of the major threats to public health in the face of climate change.

Methods

We used species distribution modelling techniques to predict the distributions of I.ricinus and I.persulcatus, using aggregated historical data from 2014 to 2020 and new tick occurrence data from 2021. By aiming to fill the gaps in tick occurrence data, we created a new sampling strategy across Finland. We also screened for tick-borne encephalitis virus (TBEV) and Borrelia from the newly collected ticks. Climate, land use and vegetation data, and population densities of the tick hosts were used in various combinations on four data sets to estimate tick species’ distributions across mainland Finland with a 1-km resolution.

Results

In the 2021 survey, 89 new locations were sampled of which 25 new presences and 63 absences were found for I.ricinus and one new presence and 88 absences for I.persulcatus. A total of 502 ticks were collected and analysed; no ticks were positive for TBEV, while 56 (47%) of the 120 pools, including adult, nymph, and larva pools, were positive for Borrelia (minimum infection rate 11.2%, respectively). Our prediction results demonstrate that two combined predictor data sets based on ensemble mean models yielded the highest predictive accuracy for both I.ricinus (AUC = 0.91, 0.94) and I.persulcatus (AUC = 0.93, 0.96). The suitable habitats for I.ricinus were determined by higher relative humidity, air temperature, precipitation sum, and middle-infrared reflectance levels and higher densities of white-tailed deer, European hare, and red fox. For I.persulcatus, locations with greater precipitation and air temperature and higher white-tailed deer, roe deer, and mountain hare densities were associated with higher occurrence probabilities. Suitable habitats for I.ricinus ranged from southern Finland up to Central Ostrobothnia and North Karelia, excluding areas in Ostrobothnia and Pirkanmaa. For I.persulcatus, suitable areas were located along the western coast from Ostrobothnia to southern Lapland, in North Karelia, North Savo, Kainuu, and areas in Pirkanmaa and Päijät-Häme.

Conclusions

This is the first study conducted in Finland that estimates potential tick species distributions using environmental and host data. Our results can be utilized in vector control strategies, as supporting material in recommendations issued by public health authorities, and as predictor data for modelling the risk for tick-borne diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05410-8.

Culture Isolate of Rickettsia felis from a Tick

Although the cat flea, Ctenocephalides felis, has been identified as the primary vector of Rickettsia felis, additional flea, tick, mite, and louse species have also been associated with this bacterium by molecular means; however, the role of these arthropods in the transmission of R. felis has not been clarified. Here, we succeeded in culture isolation of R. felis from a host-seeking castor bean tick, Ixodes ricinus, the most common tick in Slovakia. The bacterial isolation was performed on XTC-2 cells at 28 °C using the shell-vial technique. An evaluation of the growth properties was performed for both the XTC-2 and Vero cell lines. We observed R. felis in the infected host cells microscopically by Gimenez staining and immunofluorescence assay. The R. felis isolate was purified by gradient ultracentrifugation and visualized by electron microscopy. Fragments of the genes gltA, ompA, ompB, htrA, rpoB, sca4, rffE, and rrs were amplified and compared with the corresponding sequences of the type strain URRWXCal2 and other R. felis culture -isolated strains. We did not detect any nucleotide polymorphisms; however, plasmid pRFδ, characteristic of the standard strain, was absent in our isolate. Herein, we describe the first successful isolation and characterization of a tick-derived R. felis strain “Danube”, obtained from an I. ricinus nymph.

Structural analysis of the outer surface proteins from Borrelia burgdorferi paralogous gene family 54 that are thought to be the key players in the pathogenesis of Lyme disease

Lyme disease is a tick-borne infection caused by Borrelia burgdorferi sensu lato complex spirochetes. Through a complex enzootic cycle, the bacteria transfer between two different hosts: Ixodes ticks and mammalian organisms. At the start of the tick blood meal, the spirochetes located in the tick gut upregulate the expression of several genes, mainly coding for outer surface proteins. Outer surface proteins belonging to the paralogous gene family 54 (PFam54) have been shown to be the most upregulated among the other borrelial proteins and the results clearly point to the potential importance of these proteins in the pathogenesis of Lyme disease. The significance of PFam54 proteins is confirmed by the fact that of all ten PFam54 proteins, BBA64 and BBA66 are necessary for the transfer of B. burgdorferi from infected Ixodes ticks to mammalian hosts. To enhance the understanding of the pathogenesis of Lyme disease and to promote the development of novel therapies against Lyme disease, we solved the crystal structure of the PFam54 member BBA65. Additionally, we report the structure of the B. burgdorferi BBA64 orthologous protein from B. spielmanii. Together with the previously determined crystal structures of five PFam54 members and several related proteins, we performed a comprehensive structural analysis for this important group of proteins. In addition to revealing the molecular aspects of the proteins, the structural data analysis suggests that the gene families PFam54 and PFam60, which have long been referred to as separate paralogous families, should be merged into one and designated as PFam54_60.

Assessing systemic and non-systemic transmission risk of tick-borne encephalitis virus in Hungary

Estimating the tick-borne encephalitis (TBE) infection risk under substantial uncertainties of the vector abundance, environmental condition and human-tick interaction is important for evidence-informed public health intervention strategies. Estimating this risk is computationally challenging since the data we observe, i.e., the human incidence of TBE, is only the final outcome of the tick-host transmission and tick-human contact processes. The challenge also increases since the complex TBE virus (TBEV) transmission cycle involves the non-systemic route of transmission between co-feeding ticks. Here, we describe the hidden Markov transition process, using a novel TBEV transmission-human case reporting cascade model that couples the susceptible-infected compartmental model describing the TBEV transmission dynamics among ticks, animal hosts and humans, with the stochastic observation process of human TBE reporting given infection. By fitting human incidence data in Hungary to the transmission model, we estimate key parameters relevant to the tick-host interaction and tick-human transmission. We then use the parametrized cascade model to assess the transmission potential of TBEV in the enzootic cycle with respect to the climate change, and to evaluate the contribution of non-systemic transmission. We show that the TBEV transmission potential in the enzootic cycle has been increasing along with the increased temperature though the TBE human incidence has dropped since 1990s, emphasizing the importance of persistent public health interventions. By demonstrating that non-systemic transmission pathway is a significant factor in the transmission of TBEV in Hungary, we conclude that the risk of TBE infection will be highly underestimated if the non-systemic transmission route is neglected in the risk assessment.

Seasonal Patterns in the Prevalence and Diversity of Tick-Borne Borrelia burgdorferi Sensu Lato, Anaplasma phagocytophilum and Rickettsia spp. in an Urban Temperate Forest in South Western Slovakia

In Europe, Ixodes ricinus is the most important vector of tick-borne zoonotic bacteria. It transmits spirochaetes from the Borrelia burgdorferi sensu lato complex, Anaplasma phagocytophilum and Rickettsia spp. Although spatial differences in the prevalence of tick-borne pathogens have been intensively studied, seasonal (within-year) fluctuations in the prevalence of these pathogens within sites are often overlooked. We analyzed the occurrence and seasonal dynamics of Ixodes ricinus in an urban forest in Bratislava, Slovakia. Furthemore, we examined temporal trends in the community structure of B. burgdorferi s.l., A. phagocytophilum and Rickettsia spp. in questing and bird-feeding ticks. The total prevalence for B. burgdorferi s.l. in questing I. ricinus was 6.8%, involving six genospecies with the dominance of bird-associated B. garinii and B. valaisiana.A. phagocytophilum, R. helvetica and R. monacensis occurred in 5.9%, 5.0% and 0.2% of questing ticks, respectively. In total, 12.5% and 4.4% of bird-feeding I. ricinus ticks carried B. burgdorferi s.l. and R. helvetica. The total prevalence of B. burgdorferi s.l. in our study site was two times lower than the mean prevalence for Europe. In contrast, A. phagocytophilum prevalence was significantly higher compared to those in other habitats of Slovakia. Our results imply that tick propagation and the transmission, suppression and seasonal dynamics of tick-borne pathogens at the study site were primarily shaped by abundance and temporal population fluctuations in ruminant and bird hosts.

High prevalence of Rickettsia helvetica in wild small mammal populations in Germany

Since the beginning of the 21st century, spotted fever rickettsioses are known as emerging diseases worldwide. Rickettsiae are obligately intracellular bacteria transmitted by arthropod vectors. The ecology of Rickettsia species has not been investigated in detail, but small mammals are considered to play a role as reservoirs. Aim of this study was to monitor rickettsiae in wild small mammals over a period of five years in four federal states of Germany. Initial screening of ear pinna tissues of 3939 animals by Pan-Rick real-time PCR targeting the citrate synthase (gltA) gene revealed 296 rodents of seven species and 19 shrews of two species positive for rickettsial DNA. Outer membrane protein gene (ompB, ompAIV) PCRs based typing resulted in the identification of three species: Rickettsia helvetica (90.9%) was found as the dominantly occurring species in the four investigated federal states, but Rickettsia felis (7.8%) and Rickettsia raoultii (1.3%) were also detected. The prevalence of Rickettsia spp. in rodents of the genus Apodemus was found to be higher (approximately 14%) than in all other rodent and shrew species at all investigated sites. General linear mixed model analyses indicated that heavier (older) individuals of yellow-necked mice and male common voles seem to contain more often rickettsial DNA than younger ones. Furthermore, rodents generally collected in forests in summer and autumn more often carried rickettsial DNA. In conclusion, this study indicated a high prevalence of R. helvetica in small mammal populations and suggests an age-dependent increase of the DNA prevalence in some of the species and in animals originating from forest habitats. The finding of R. helvetica and R. felis DNA in multiple small mammal species may indicate frequent trans-species transmission by feeding of vectors on different species. Further investigations should target the reason for the discrepancy between the high rickettsial DNA prevalence in rodents and the so far almost absence of clinical apparent human infections.

Seasonal cycles of the TBE and Lyme borreliosis vector Ixodes ricinus modelled with time-lagged and interval-averaged predictors

Ticks of the species Ixodes ricinus (L.) are the major vectors for tick-borne diseases in Europe. The aim of this study was to quantify the influence of environmental variables on the seasonal cycle of questing I. ricinus. Therefore, an 8-year time series of nymphal I. ricinus flagged at monthly intervals in Haselmühl (Germany) was compiled. For the first time, cross correlation maps were applied to identify optimal associations between observed nymphal I. ricinus densities and time-lagged as well as temporal averaged explanatory variables. To prove the explanatory power of these associations, two Poisson regression models were generated. The first model simulates the ticks of the entire time series flagged per 100 m[Formula: see text], the second model the mean seasonal cycle. Explanatory variables comprise the temperature of the flagging month, the relative humidity averaged from the flagging month and 1 month prior to flagging, the temperature averaged over 4-6 months prior to the flagging event and the hunting statistics of the European hare from the preceding year. The first model explains 65% of the monthly tick variance and results in a root mean square error (RMSE) of 17 ticks per 100 m[Formula: see text]. The second model explains 96% of the tick variance. Again, the accuracy is expressed by the RMSE, which is 5 ticks per 100 m[Formula: see text]. As a major result, this study demonstrates that tick densities are higher correlated with time-lagged and temporal averaged variables than with contemporaneous explanatory variables, resulting in a better model performance.

Dampening of population cycles in voles affects small mammal community structure, decreases diversity, and increases prevalence of a zoonotic disease

Long-term decline and depression of density in cyclic small rodents is a recent widespread phenomenon. These observed changes at the population level might have cascading effects at the ecosystem level. Here, we assessed relationships between changing boreal landscapes and biodiversity changes of small mammal communities. We also inferred potential effects of observed community changes for increased transmission risk of Puumala virus (PUUV) spread, causing the zoonotic disease nephropatica epidemica in humans. Analyses were based on long-term (1971-2013) monitoring data of shrews and voles representing 58 time series in northern Sweden. We calculated richness, diversity, and evenness at alpha, beta, and gamma level, partitioned beta diversity into turnover (species replacement) and nestedness (species addition/removal), used similarity percentages (SIMPER) analysis to assess community structure, and calculated the cumulated number of PUUV-infected bank voles and average PUUV prevalence (percentage of infected bank voles) per vole cycle. Alpha, beta, and gamma richness and diversity of voles, but not shrews, showed long-term trends that varied spatially. The observed patterns were associated with an increase in community contribution of bank vole (Myodes glareolus), a decrease of gray-sided vole (M. rufocanus) and field vole (Microtus agrestis) and a hump-shaped variation in contribution of common shrew (Sorex araneus). Long-term biodiversity changes were largely related to changes in forest landscape structure. Number of PUUV-infected bank voles in spring was negatively related to beta and gamma diversity, and positively related to turnover of shrews (replaced by voles) and to community contribution of bank voles. The latter was also positively related to average PUUV prevalence in spring. We showed that long-term changes in the boreal landscape contributed to explain the decrease in biodiversity and the change in structure of small mammal communities. In addition, our results suggest decrease in small mammal diversity to have knock-on effects on dynamics of infectious diseases among small mammals with potential implications for disease transmission to humans.

Tick infestation of small mammals in an English woodland

Tick infestations on small mammals were studied from April to November, 2010, in deciduous woodland in southern England in order to determine whether co-infestations with tick stages occurred on small mammals, a key requirement for endemic transmission of tick-borne encephalitis virus (TBEV). A total of 217 small mammals was trapped over 1,760 trap nights. Yellow-necked mice (Apodemus flavicollis) made up the majority (52.5%) of animals, followed by wood mice (A. sylvaticus) 35.5% and bank voles (Myodes glareolus) 12%. A total of 970 ticks was collected from 169 infested animals; 96% of ticks were Ixodes ricinus and 3% I. trianguliceps. Over 98% of ticks were larval stages. Mean infestation intensities of I. ricinus were significantly higher on A. flavicollis (6.53 ± 0.67) than on A. sylvaticus (4.96 ± 0.92) and M. glareolus (3.25 ± 0.53). Infestations with I. ricinus were significantly higher in August than in any other month. Co-infestations with I. ricinus nymphs and larvae were observed on six (3.6%) infested individuals, and fifteen small mammals (8.9%) supported I. ricinus - I. trianguliceps co-infestations. This work contributes further to our understanding of European small mammal hosts that maintain tick populations and their associated pathogens, and indicates that co-infestation of larvae and nymph ticks does occur in lowland UK. The possible implications for transmission of tick-borne encephalitis virus between UK ticks and small mammals are discussed.

Ixodid ticks parasitizing wild carnivores in Romania

In Romania, data regarding hard-tick diversity and tick-host associations in wild carnivores are scarce. We aimed to identify tick species in wild carnivores and to establish reliable data on tick-host associations. The study was conducted in various Romanian localities from all five ecoregions found in the country. Fourteen species of wild carnivores were examined. Immature and adult ticks were collected and identified using the morphological keys. The frequency and mean intensity of tick infestation, overall and differentiated by species, developmental stage and host were calculated. Of 202 wild carnivores, 68 were parasitized by seven tick species (predominantly Ixodes ricinus, I. hexagonus and Dermacentor reticulatus). The mean intensity of tick infestation was similar in males (6.97, BCa 95% CI 5.15-9.88) and females (5.76, BCa 95% CI 4.15-9.17). The highest prevalence of infested animals was recorded in the pannonian and steppic ecoregions, 66.7 and 52.7%, respectively. In the continental ecoregion the prevalence was 26.7%, whereas in the pontic ecoregion it was 28%. The lowest value, 16.7% was recorded in the alpine ecoregion. In total 430 ticks were collected, and 24.8% (n = 50) of the animals were infested with more than one tick species. Fourteen new tick-host associations were recorded. Our results suggest that anthropogenic changes of the environment lead to the diminishing of the boundaries, between wild and domestic animals, increasing the exposure for both animals and humans, to infective agents, including tick-borne pathogens.

Chlamydia-Like Organisms (CLOs) in Finnish Ixodes ricinus Ticks and Human Skin

Ticks carry several human pathogenic microbes including Borreliae and Flavivirus causing tick-born encephalitis. Ticks can also carry DNA of Chlamydia-like organisms (CLOs). The purpose of this study was to investigate the occurrence of CLOs in ticks and skin biopsies taken from individuals with suspected tick bite. DNA from CLOs was detected by pan-Chlamydiales-PCR in 40% of adult ticks from southwestern Finland. The estimated minimal infection rate for nymphs and larvae (studied in pools) was 6% and 2%, respectively. For the first time, we show CLO DNA also in human skin as 68% of all skin biopsies studied contained CLO DNA as determined through pan-Chlamydiales-PCR. Sequence analyses based on the 16S rRNA gene fragment indicated that the sequences detected in ticks were heterogeneous, representing various CLO families; whereas the majority of the sequences from human skin remained "unclassified Chlamydiales" and might represent a new family-level lineage. CLO sequences detected in four skin biopsies were most closely related to "uncultured Chlamydial bacterium clones from Ixodes ricinus ticks" and two of them were very similar to CLO sequences from Finnish ticks. These results suggest that CLO DNA is present in human skin; ticks carry CLOs and could potentially transmit CLOs to humans.

Susceptibility to Ticks and Lyme Disease Spirochetes Is Not Affected in Mice Coinfected with Nematodes

Small rodents serve as reservoir hosts for tick-borne pathogens, such as the spirochetes causing Lyme disease. Whether natural coinfections with other macroparasites alter the success of tick feeding, antitick immunity, and the host's reservoir competence for tick-borne pathogens remains to be determined. In a parasitological survey of wild mice in Berlin, Germany, approximately 40% of Ixodes ricinus-infested animals simultaneously harbored a nematode of the genus Heligmosomoides. We therefore aimed to analyze the immunological impact of the nematode/tick coinfection as well as its effect on the tick-borne pathogen Borrelia afzelii. Hosts experimentally coinfected with Heligmosomoides polygyrus and larval/nymphal I. ricinus ticks developed substantially stronger systemic type 2 T helper cell (Th2) responses, on the basis of the levels of GATA-3 and interleukin-13 expression, than mice infected with a single pathogen. During repeated larval infestations, however, anti-tick Th2 reactivity and an observed partial immunity to tick feeding were unaffected by concurrent nematode infections. Importantly, the strong systemic Th2 immune response in coinfected mice did not affect susceptibility to tick-borne B. afzelii. An observed trend for decreased local and systemic Th1 reactivity against B. afzelii in coinfected mice did not result in a higher spirochete burden, nor did it facilitate bacterial dissemination or induce signs of immunopathology. Hence, this study indicates that strong systemic Th2 responses in nematode/tick-coinfected house mice do not affect the success of tick feeding and the control of the causative agent of Lyme disease.

Epidemiological Implications of Host Biodiversity and Vector Biology: Key Insights from Simple Models

Models used to investigate the relationship between biodiversity change and vector-borne disease risk often do not explicitly include the vector; they instead rely on a frequency-dependent transmission function to represent vector dynamics. However, differences between classes of vector (e.g., ticks and insects) can cause discrepancies in epidemiological responses to environmental change. Using a pair of disease models (mosquito- and tick-borne), we simulated substitutive and additive biodiversity change (where noncompetent hosts replaced or were added to competent hosts, respectively), while considering different relationships between vector and host densities. We found important differences between classes of vector, including an increased likelihood of amplified disease risk under additive biodiversity change in mosquito models, driven by higher vector biting rates. We also draw attention to more general phenomena, such as a negative relationship between initial infection prevalence in vectors and likelihood of dilution, and the potential for a rise in density of infected vectors to occur simultaneously with a decline in proportion of infected hosts. This has important implications; the density of infected vectors is the most valid metric for primarily zoonotic infections, while the proportion of infected hosts is more relevant for infections where humans are a primary host.

Effect of landscape features on the relationship between Ixodes ricinus ticks and their small mammal hosts

Background

The consequences of land use changes are among the most cited causes of emerging infectious diseases because they can modify the ecology and transmission of pathogens. This is particularly true for vector-borne diseases which depend on abiotic (e.g. climate) and biotic conditions (i.e. hosts and vectors). In this study, we investigated how landscape features affect the abundances of small mammals and Ixodes ricinus ticks, and how they influence their relationship.

Methods

From 2012 to 2014, small mammals and questing I. ricinus ticks were sampled in spring and autumn in 24 sites located in agricultural and forest landscapes in Brittany, France. We tested the effects of landscape features (composition and configuration) on the abundances of small mammal species and immature ticks and their relationship. Additionally, we quantified the larval tick burden of small mammals in 2012 to better describe this relationship.

Results

The nymph abundance was positively influenced by the larval occurrence and the wood mouse Apodemus sylvaticus abundance the previous spring because they hosted tenfold more larvae than the bank vole Myodes glareolus. The bank vole abundance in spring and autumn had a negative and positive effect, respectively, on the nymph abundance. In agricultural landscapes, wood mice were positively influenced by woodland cover and woodland/hedgerow-grassland ecotone, whereas bank voles showed the opposite or non-significant responses to these landscape variables. The woodland cover had a positive effect on immature ticks.

Conclusion

The landscape configuration, likely by affecting the landscape connectivity, influences the small mammal communities in permanent habitats. Our study showed that the wood mouse, due to its dominance and to its tolerance to ticks, feeds a substantial proportion of larvae. The acquired resistance to ticks in the bank vole can reduce its role as a trophic resource over time. The nymph abundance seems indirectly influenced by landscape features via their effects on the small mammal community. To enhance our understanding of the epidemiology of tick-borne diseases within landscapes, further studies will integrate data on pathogen prevalence and investigate explicitly the effect of landscape connectivity on host-vector-pathogen systems.

Multi-trophic interactions driving the transmission cycle of Borrelia afzelii between Ixodes ricinus and rodents: a review

The tick Ixodes ricinus is the main vector of the spirochaete Borrelia burgdorferi sensu lato, the causal agent of Lyme borreliosis, in the western Palearctic. Rodents are the reservoir host of B. afzelii, which can be transmitted to I. ricinus larvae during a blood meal. The infected engorged larvae moult into infected nymphs, which can transmit the spirochaetes to rodents and humans. Interestingly, even though only about 1 % of the larvae develop into a borreliae-infected nymph, the enzootic borreliae lifecycle can persist. The development from larva to infected nymph is a key aspect in this lifecycle, influencing the density of infected nymphs and thereby Lyme borreliosis risk. The density of infected nymphs varies temporally and geographically and is influenced by multi-trophic (tick-host-borreliae) interactions. For example, blood feeding success of ticks and spirochaete transmission success differ between rodent species and host-finding success appears to be affected by a B. afzelii infection in both the rodent and the tick. In this paper, we review the major interactions between I. ricinus, rodents and B. afzelii that influence this development, with the aim to elucidate the critical factors that determine the epidemiological risk of Lyme borreliosis. The effects of the tick, rodent and B. afzelii on larval host finding, larval blood feeding, spirochaete transmission from rodent to larva and development from larva to nymph are discussed. Nymphal host finding, nymphal blood feeding and spirochaete transmission from nymph to rodent are the final steps to complete the enzootic B. afzelii lifecycle and are included in the review. It is concluded that rodent density, rodent infection prevalence, and tick burden are the major factors affecting the development from larva to infected nymph and that these interact with each other. We suggest that the B. afzelii lifecycle is dependent on the aggregation of ticks among rodents, which is manipulated by the pathogen itself. Better understanding of the processes involved in the development and aggregation of ticks results in more precise estimates of the density of infected nymphs, and hence predictions of Lyme borreliosis risk.

The vector tick Ixodes ricinus feeding on an arboreal rodent-the edible dormouse Glis glis

The reservoir competence and long life expectancy of edible dormice, Glis glis, suggest that they serve as efficient reservoir hosts for Lyme disease (LD) spirochetes. Their arboreality, however, may reduce the probability to encounter sufficient questing Ixodes ricinus ticks to acquire and perpetuate LD spirochetes. To define the potential role of this small arboreal hibernator in the transmission cycle of LD spirochetes, we examined their rate and density of infestation with subadult ticks throughout the season of activity. Of the 1081 edible dormice that we captured at five study sites in Southern Germany and inspected for ticks at 2946 capture occasions, 26 % were infested with at least one and as many as 26 subadult ticks on their ear pinnae. The distribution of ticks feeding on edible dormice was highly aggregated. Although only few individuals harbored nymphal ticks soon after their emergence from hibernation, the rate of nymphal infestation increased steadily throughout the season and reached about 35 % in September. Dormice inhabiting a site with few conspecifics seemed more likely to be infested by numerous ticks, particularly nymphs, than those individuals living in densely populated sites. Male dormice were more likely to be parasitized by numerous nymphs than were females, independent of their age and body mass. Our observation that season, population density, and sex affect the rates of ticks feeding on edible dormice suggests that the contribution of edible dormice to the transmission cycle of LD spirochetes depends mainly on their ranging behavior and level of activity.

The generalist tick Ixodes ricinus and the specialist tick Ixodes trianguliceps on shrews and rodents in a northern forest ecosystem--a role of body size even among small hosts

Background

Understanding aggregation of ticks on hosts and attachment of life stages to different host species, are central components for understanding tick-borne disease epidemiology. The generalist tick, Ixodes ricinus, is a well-known vector of Lyme borrelioses, while the specialist tick, Ixodes trianguliceps, feeding only on small mammals, may play a role in maintaining infection levels in hosts. In a northern forest in Norway, we aimed to quantify the role of different small mammal species in feeding ticks, to determine the extent to which body mass, even among small mammals, plays a role for tick load, and to determine the seasonal pattern of the two tick species.

Methods

Small mammals were captured along transects in two nearby areas along the west coast of Norway. All life stages of ticks were counted. Tick load, including both prevalence and intensity, was analysed with negative binomial models.

Results

A total of 359 rodents and shrews were captured with a total of 1106 I. ricinus (60.0 %) and 737 I. trianguliceps (40.4 %), consisting of 98.2 % larvae and 1.8 % nymphs of I. ricinus and 91.2 % larvae, 8.7 % nymphs and 0.1 % adult females of I. trianguliceps. Due to high abundance, Sorex araneus fed most of the larvae of both tick species (I. ricinus 61.9 %, I. trianguliceps 64.9 %) with Apodemus sylvaticus (I. ricinus 20.4 %, I. trianguliceps 10.0 %) and Myodes glareolus (I. ricinus 10.9 %, I. trianguliceps 9.5 %) as the next most important hosts. Individual A. sylvaticus and M. glareolus had higher infestation intensity than S. araneus, while Sorex minutus had markedly lower infestation intensity. The load of I. ricinus larvae and nymphs was related to body mass mainly up to ~10 g, while the load of I. trianguliceps was less dependent of body mass. The load of I. trianguliceps was higher in spring than in fall, while the seasonal pattern was reversed for I. ricinus with higher loads in fall.

Conclusions

Body mass was important for explaining load of I. ricinus mainly up to a body mass of ~10 g across a range of smaller mammalian hosts. Consistent with earlier work elsewhere in Europe, we found the highest tick infestation intensity on the wood mouse A. sylvaticus. However, this rodent species fed only 20.4 % of all I. ricinus larvae, while the much more abundant S. araneus fed 61.9 %. Our study emphasizes an important quantitative role of the common shrew S. araneus as a main host to I. ricinus larvae and to both I. trianguliceps larvae and nymphs. The partly seasonal distinct attachment pattern of I. ricinus and I. trianguliceps is evidence for niche separation.

Prevalence of infection with Rickettsia helvetica in Ixodes ricinus ticks feeding on non-rickettsiemic rodent hosts in sylvatic habitats of west-central Poland

Ixodes ricinus is the most prevalent and widely distributed tick species in European countries and plays a principal role in transmission of a wide range of microbial pathogens. It is also a main vector and reservoir of Rickettsia spp. of the spotted fever group with the infection level ranging in Poland from 1.3% to 11.4%. Nevertheless, little research has been conducted so far to identify reservoir hosts for these pathogens. A survey was undertaken to investigate the presence of Rickettsia spp. in wild small rodents and detached I. ricinus. Rodents, Apodemus flavicollis mice and Myodes glareolus voles were captured in typically sylvatic habitats of west-central Poland. Blood samples and collected ticks were analyzed by conventional, semi-nested and nested PCRs. Rickettsial species were determined by sequence analysis of obtained fragments of gltA and 16S rRNA genes. A total of 2339 immature I. ricinus (mostly larvae) were collected from 158 animals. Proportion of hosts carrying ticks was 84%, being higher for A. flavicollis than for M. glareolus. Rickettsia helvetica, the only species identified, was detected in 8% of 12 nymphs and in at least 10.7% (MIR) of 804 larvae investigated. Prevalence of infected ticks on both rodent species was comparable (10.8 vs. 9%). None of blood samples tested was positive for Rickettsia spp. The results showed that in sylvatic habitats the level of infestation with larval I. ricinus was higher in A. flavicollis mice in comparison with M. glareolus voles. They show that R. helvetica frequently occurred in ticks feeding on rodents. Positive immature ticks were collected from non-rickettsiemic hosts what might suggest a vertical route of their infection (transovarial and/or transstadial) or a very short-lasting rickettsiemia in rodents. A natural vertebrate reservoir host for R. helvetica remains to be determined.

Abiotic predictors and annual seasonal dynamics of Ixodes ricinus, the major disease vector of Central Europe

BACKGROUND

Abiotic conditions provide cues that drive tick questing activity. Defining these cues is critical in predicting biting risk, and in forecasting climate change impacts on tick populations. This is particularly important for Ixodes ricinus nymphs, the vector of numerous pathogens affecting humans.

METHODS

A 6-year study of the questing activity of I. ricinus was conducted in Central Bohemia, Czech Republic, from 2001 to 2006. Tick numbers were determined by weekly flagging the vegetation in a defined 600 m(2) field site. After capture, ticks were released back to where they were found. Concurrent temperature data and relative humidity were collected in the microhabitat and at a nearby meteorological station. Data were analysed by regression methods.

RESULTS

During 208 monitoring visits, a total of 21,623 ticks were recorded. Larvae, nymphs, and adults showed typical bimodal questing activity curves with major spring peaks and minor late summer or autumn peaks (mid-summer for males). Questing activity of nymphs and adults began with ~12 h of daylight and ceased at ~9 h daylight, at limiting temperatures close to freezing (in early spring and late autumn); questing occurred during ~70 % calendar year without cessation in summer. The co-occurrence of larvae and nymphs varied annually, ranging from 31 to 80 % of monitoring visits, and depended on the questing activity of larvae. Near-ground temperature, day length, and relative air humidity were all significant predictors of nymphal activity. For 70 % of records, near-ground temperatures measured in the microhabitat were 4-5 °C lower than those recorded by the nearby meteorological observatory, although they were strongly dependent. Inter-annual differences in seasonal numbers of nymphs reflected extreme weather events.

CONCLUSIONS

Weather predictions (particularly for temperature) combined with daylight length, are good predictors of the initiation and cessation of I. ricinus nymph questing activity, and hence of the risk period to humans, in Central Europe. Co-occurrence data for larvae and nymphs support the notion of intrastadial rather than interstadial co-feeding pathogen transmission. Annual questing tick numbers recover quickly from the impact of extreme weather events.

Host preferences of immature Dermacentor reticulatus (Acari: Ixodidae) in a forest habitat in Germany

Dermacentor reticulatus is widespread throughout Europe and is expanding its range in several European countries. It is associated with a number of different pathogens. Its role in the transmission of disease to humans is currently small; however, it might play an important role in the maintenance of pathogens in enzootic cycles. The ecology of D. reticulatus, especially of the immatures, is not well known. In this study, ticks from small mammals, caught in a capture-mark-release study between May 2012 and October 2014 in a unique woodland area close to Karlsruhe, Germany, were collected. The main host species trapped were the yellow-necked mouse (Apodemus flavicollis) and the bank vole (Myodes glareolus). Small mammal populations showed high variability in their density between the study years, which is probably due to harsh winter conditions in 2012/2013 and missing mast leading to high winter mortality. Larvae and nymphs of D. reticulatus were predominantly found in July and August, respectively, and the infestation rates among the different small mammal species suggest a host preference of D. reticulatus for M. glareolus.

Search for blood or water is influenced by Borrelia burgdorferi in Ixodes ricinus

An increasing number of studies suggest that vector-borne parasites are able to alter phenotypic traits in their arthropod vectors so that microorganism transmission is enhanced. This review documents this phenomenon, which occurs between Borrelia burgdorferi bacteria, the causative agents of Lyme borreliosis, and their tick vectors belonging to the Ixodes ricinus complex. It also reviews the influence of other tick-borne pathogens on these ticks. Ticks belonging to the Ixodes ricinus complex benefit from Borrelia infection by an increased lifespan (more fat and more resistance to desiccation) and by an increased questing period (less need to move to the litter zone to rehydrate), which enhances tick chances to find a host and to subsequently transmit the pathogens.

Tracking the sources of blood meals of parasitic arthropods using shotgun proteomics and unidentified tandem mass spectral libraries

Identifying the species on which hematophagous arthropods feed is crucial for studying the factors that affect pathogen distributions and that can aid public health. Here we describe a protocol to identify the species a parasitic arthropod has previously fed upon by identifying the source of the remnants of a previous blood meal via shotgun proteomics and spectral matching. The protocol is a nontargeted approach that uses the entire detected blood proteome for source identification; it does not require a priori knowledge of genome or protein sequences. Instead, reference spectral libraries are compiled from the blood of multiple host species by using SpectraST, which takes ∼4 d; the identification of the species from which a previous blood meal of a hematophagous arthropod was taken is achieved with spectral matching against the reference spectral libraries, which takes approximately another 4 d. This method is robust against random degradation of the blood meal and can identify unknown blood remnants months after the feeding event.

Identifying sources of tick blood meals using unidentified tandem mass spectral libraries

Rapid and reliable identification of the vertebrate species on which a disease vector previously parasitized is imperative to study ecological factors that affect pathogen distribution and can aid the development of public health programs. Here we describe a proteome profiling technique designed to identify the source of blood meals of hematophagous arthropods. This method employs direct spectral matching and thus does not require a priori knowledge of any genetic or protein sequence information. Using this technology, we detect remnants of blood in blacklegged ticks (Ixodes scapularis) and correctly determine the vertebrate species from which the blood was derived even six months after the tick had fed. This biological fingerprinting methodology is sensitive, fast, cost-effective, and can potentially be adapted for other biological and medical applications when existing genome-based methods are impractical or ineffective.

The role of rodents in the ecology of Ixodes ricinus and associated pathogens in Central and Eastern Europe

Rodents comprise more species than any other mammal order. Most rodents are considered keystone species in their ecological communities, hence the survival of many other species in the ecosystem depend on them. From medical point of view, this is particularly important for rodent-dependent pathogens. In the particular case of tick-borne diseases, rodents are important as hosts for vector ticks and as reservoir hosts (Lyme borreliosis, human granulocytic anaplasmosis, Crimean-Congo hemorrhagic fever, Tick-borne relapsing fevers, tick-borne rickettsioses, babesiosis). Community and population ecology of rodents was shown to be correlated with disease ecology in the case of many tick-borne diseases. In Eastern Europe, several adult hard-tick species use rodents as their principal hosts: Ixodes apronophorus, I. crenulatus, I. laguri, I. redikorzevi, I. trianguliceps. However, the majority of ticks feeding on rodents are immature stages of ticks which as adults are parasitic on larger mammals. Larvae and nymphs of Ixodes ricinus, the most abundant and medically important tick from Europe, are commonly found on rodents. This is particularly important, as many rodents are synanthropic and, together with other micromammals and birds are often the only available natural hosts for ticks in urban environments. This work reviews the correlated ecology of rodents and I. ricinus.

Seasonal and spatial occurrence of glycerol-3-phosphate dehydrogenase variability in Ixodes ricinus (Acari: Ixodidae) populations

Previous results indicate that glycerol-3-phosphate dehydrogenase variability represents the adaptation of Ixodes ricinus L. (Acari: Ixodidae) to fluctuations of environmental conditions, particularly to temperature. Analysis of crucial polymorphisms in I. ricinus Gpdh gene was done by the restriction method, and three different haplotypes were obtained (GPDH441 1, GPDH441 2, and GPDH441 3), corresponding to GPDH alleles detected by allozyme electrophoresis. Differences in GPDH441 haplotype and genotype frequencies were found between samples from open and forest habitats. Significant seasonal variations of GPDH441 haplotype and genotype frequencies were detected in samples from the open habitats. No seasonal variations were observed at forest localities, probably because of the less pronounced amplitude of environmental factors. The possible role of host availability was discussed as an important factor that affects seasonal dynamics and genetic composition of tick populations.

Ixodes ricinus ticks (Acari: Ixodidae): vectors for Lyme disease spirochetes in Romania

In this study 1,868 questing Ixodes ricinus ticks (nymphs and adults), collected in six sites from three counties--Giurgiu, Sibiu, and Tulcea--in Romania, were examined by polymerase chain reaction (PCR) followed by reverse line blot (RLB) for detection of Borrelia burgdorferi sensu lato presence. The bacteria were found in 18% of the investigated ticks. The prevalence of infection did not differ significantly between nymphs (19.1%) and adults (15.4%). Three B. burgdorferi s.l. genospecies were detected: B. afzelii (61.1%), B. garinii (31.2%), and B. valaisiana (7.7%). No mixed infections were detected. The highest infection prevalence in nymphs was detected at Cristian (Sibiu County)--22.0%, whereas in adults it was at Comana (Giurgiu County)--19.8%. This preliminary study provides evidence that Lyme disease spirochetes are present in various regions of Romania, and at a relatively high prevalence in their vectors, thus posing a risk of infection to human subjects in the areas infested by ticks.

Investigating the persistence of tick-borne pathogens via the R0model

In the epidemiology of infectious diseases, the basic reproduction number, R0, has a number of important applications, most notably it can be used to predict whether a pathogen is likely to become established, or persist, in a given area. We used the R0model to investigate the persistence of 3 tick-borne pathogens;Babesia microti, Anaplasma phagocytophilumandBorrelia burgdorferisensu lato in anApodemus sylvaticus-Ixodes ricinussystem. The persistence of these pathogens was also determined empirically by screening questing ticks and wood mice by PCR. All 3 pathogens behaved differently in response to changes in the proportion of transmission hosts on whichI. ricinusfed, the efficiency of transmission between the host and ticks and the abundance of larval and nymphal ticks found on small mammals. Empirical data supported theoretical predictions of the R0model. The transmission pathway employed and the duration of systemic infection were also identified as important factors responsible for establishment or persistence of tick-borne pathogens in a given tick-host system. The current study demonstrates how the R0model can be put to practical use to investigate factors affecting tick-borne pathogen persistence, which has important implications for animal and human health worldwide.

Geographic and temporal variations in population dynamics of Ixodes ricinus and associated Borrelia infections in The Netherlands

In a countrywide investigation of the ecological factors that contribute to Lyme borreliosis risk, a longitudinal study on population dynamics of the sheep tick Ixodes ricinus and their infections with Borrelia burgdorferi sensu lato (s.l.) was undertaken at 24 sites in The Netherlands from July 2006 to December 2007. Study sites were mature forests, dune vegetations, or new forests on land reclaimed from the sea. Ticks were sampled monthly and nymphal ticks were investigated for the presence of Borrelia spp. I. ricinus was the only tick species found. Ticks were found in all sites, but with significant spatial and temporal variations in density between sites. Peak densities were found in July and August, with lowest tick numbers collected in December and January. In some sites, questing activities of I. ricinus nymphs and adults were observed in the winter months. Mean monthly Borrelia infections in nymphs varied from 0% to 29.0% (range: 0%-60%), and several sites had significantly higher mean nymphal Borrelia infections than others. Four genospecies of Borrelia burgdorferi s.l. were found, with B. afzelii being dominant at most sites. Borrelia infection rates in nymphal ticks collected in July, September, and November 2006 were significantly higher (23.7%, p<0.01) than those in the corresponding months of 2007 (9.9%). The diversity in Borrelia genospecies between sites was significantly different (p<0.001). Habitat structure (tree cover) was an effective discriminant parameter in the determination of Borrelia infection risk, as measured by the proportion of nymphal ticks infected with B. burgdorferi s.l. Thickness of the litter layer and moss cover were positively related to nymphal and adult tick densities. The study shows that Borrelia-infected ticks are present in many forest and dune areas in The Netherlands and suggests that in such biotopes, which are used for a wide variety of recreational activities, the infection risk is high.

Factors affecting patterns of tick parasitism on forest rodents in tick-borne encephalitis risk areas, Germany

Identifying factors affecting individual vector burdens is essential for understanding infectious disease systems. Drawing upon data of a rodent monitoring programme conducted in nine different forest patches in southern Hesse, Germany, we developed models which predict tick (Ixodes spp. and Dermacentor spp.) burdens on two rodent species Apodemus flavicollis and Myodes glareolus. Models for the two rodent species were broadly similar but differed in some aspects. Patterns of Ixodes spp. burdens were influenced by extrinsic factors such as season, unexplained spatial variation (both species), relative humidity and vegetation cover (A. flavicollis). We found support for the 'body mass' (tick burdens increase with body mass/age) and for the 'dilution' hypothesis (tick burdens decline with increasing rodent densities) and little support for the 'sex-bias' hypothesis (both species). Surprisingly, roe deer densities were not correlated with larvae counts on rodents. Factors influencing the mean burden did not significantly explain the observed dispersion of tick counts. Co-feeding aggregations, which are essential for tick-borne disease transmission, were mainly found in A. flavicollis of high body mass trapped in areas with fast increase in spring temperatures. Locally, Dermacentor spp. appears to be an important parasite on A. flavicollis and M. glareolus. Dermacentor spp. was rather confined to areas with higher average temperatures during the vegetation period. Nymphs of Dermacentor spp. mainly fed on M. glareolus and were seldom found on A. flavicollis. Whereas Ixodes spp. is the dominant tick genus in woodlands of our study area, the distribution and epidemiological role of Dermacentor spp. should be monitored closely.

Prevalence of Bartonella henselae and Borrelia burgdorferi sensu lato DNA in ixodes ricinus ticks in Europe

Bartonella spp. can cause persistent bloodstream infections in humans and animals. To determine whether Bartonella henselae is present in questing Ixodes ricinus ticks, we analyzed the prevalence of B. henselae DNA among tick stages compared to the prevalence of DNA from Borrelia burgdorferi sensu lato, the pathogen most frequently transmitted by ticks. B. henselae DNA was present with a prevalence of up to approximately 40% in tick populations sampled in four European sites (Eberdingen, Germany; Klasdorf, Germany; Lembach, France; and Madeira, Portugal). The odds of detecting B. henselae DNA in nymphal ticks was approximately 14-fold higher than in adult ticks. No tick was found to be coinfected with B. henselae and B. burgdorferi sensu lato. Taken together, our data indicate that ticks might serve as a vector for the transmission of B. henselae to humans.

Risk indicators for the tick Ixodes ricinus and Borrelia burgdorferi sensu lato in Sweden

The distributional area of the tick Ixodes ricinus (L.), the primary European vector to humans of Lyme borreliosis spirochaetes (Borrelia burgdorferi sensu lato) and tick-borne encephalitis virus, appears to be increasing in Sweden. It is therefore important to determine which environmental factors are most useful to assess risk of human exposure to this tick and its associated pathogens. The geographical distribution of I. ricinus in Sweden was analysed with respect to vegetation zones and climate. The northern limit of I. ricinus and B. burgdorferi s.l. in Sweden corresponds roughly to the northern limit of the southern boreal vegetation zone, and is characterized climatically by snow cover for a mean duration of 150 days and a vegetation period averaging 170 days. The zoogeographical distribution of I. ricinus in Sweden can be classified as southerly-central, with the centre of the distribution south of the Limes Norrlandicus. Ixodes ricinus nymphs from 13 localities in different parts of Sweden were examined for the presence of B. burgdorferi s.l. and found to be infected with Borrelia afzelii and Borrelia garinii. Tick sampling localities were characterized on the basis of the density of Borrelia-infected I. ricinus nymphs, presence of specific mammals, dominant vegetation and climate. Densities of I. ricinus nymphs and Borrelia-infected nymphs were significantly correlated, and nymphal density can thus serve as a general indicator of risk for exposure to Lyme borreliosis spirochaetes. Analysis of data from this and other studies suggests that high densities of Borrelia-infected nymphs typically occur in coastal, broadleaf vegetation and in mixed deciduous/spruce vegetation in southern Sweden. Ixodes ricinus populations consistently infected with B. burgdorferi s.l. can occur in: (a) biotopes with shrews, rodents, hares and birds; (b) biotopes with shrews, rodents, hares, deer and birds, and (c) island locations where the varying hare (Lepus timidus) is the only mammalian tick host.

Reviewing molecular adaptations of Lyme borreliosis spirochetes in the context of reproductive fitness in natural transmission cycles

Lyme borreliosis (LB) is caused by a group of pathogenic spirochetes – most often Borrelia burgdorferi, B. afzelii, and B. garinii – that are vectored by hard ticks in the Ixodes ricinus-persulcatus complex, which feed on a variety of mammals, birds, and lizards. Although LB is one of the best-studied vector-borne zoonoses, the annual incidence in North America and Europe leads other vector-borne diseases and continues to increase. What factors make the LB system so successful, and how can researchers hope to reduce disease risk – either through vaccinating humans or reducing the risk of contacting infected ticks in nature? Discoveries of molecular interactions involved in the transmission of LB spirochetes have accelerated recently, revealing complex interactions among the spirochete-tick-vertebrate triad. These interactions involve multiple, and often redundant, pathways that reflect the evolution of general and specific mechanisms by which the spirochetes survive and reproduce. Previous reviews have focused on the molecular interactions or population biology of the system. Here molecular interactions among the LB spirochete, its vector, and vertebrate hosts are reviewed in the context of natural maintenance cycles, which represent the ecological and evolutionary contexts that shape these interactions. This holistic system approach may help researchers develop additional testable hypotheses about transmission processes, interpret laboratory results, and guide development of future LB control measures and management.

Assessment of the risk of contracting Lyme disease in areas with significant human presence

In order to describe seasonal changes in Lyme diseases risk rate at three localities in Serbia, during the period of 2003-2005, a total of 1542 Ixodes ricinus ticks (493 nymphs, 525 females and 524 males) were examined. The prevalence of Borrelia burgdorferi in Ixodes ricinus ticks at the Bovan Lake County were higher than the average for European localities (45.9% for adults and 18.8% for nymphs). In Mt. Avala and Kljajicevo counties adults and nymphs were, respectively, infected at the following percentages: 26.3, 10.7; 16.2 and 7.6%. The outcome indicates a relatively high risk of the contracting Lyme disease in all investigates areas.

The role of lizards in the ecology of Lyme disease in two endemic zones of the northeastern United States

We examined the role of lizards in the ecology of Lyme disease in New York and Maryland. We collected data on vector tick infestations, measured lizard "realized" reservoir competence for the Lyme disease spirochete Borrelia burgdorferi, and estimated lizard population density. These data were incorporated into a model that predicts a host's ability to influence the prevalence of B. burgdorferi in the tick population, a primary risk factor in the epidemiology of Lyme disease. Published data on other northeastern hosts were included in the model to provide a reference for interpreting the importance of lizards as hosts. The model results indicate that 5-lined skinks (Eumeces fasciatus) are dilution hosts, capable of reducing infection prevalence in the tick population by 10.7-51.5 percentage points, whereas eastern fence lizards (Sceloporus undulatus) are not dilution hosts in the areas studied. Owing to moderate burdens of larval ticks, relatively high population densities, and reservoir incompetence, E. fasciatus may play an important role in the ecology of Lyme disease by reducing vector infection prevalence and associated human risk of infection.

Infestation of sand lizards (Lacerta agilis) resident in the Northeastern Poland by Ixodes ricinus (L.) ticks and their infection with Borrelia burgdorferi sensu lato

Sand lizards (Lacerta agilis) were trapped and examined for ticks from May to September in 2002 and 2003 in Northeastern Poland. A total of 233 Ixodes ricinus (L.) ticks (76 larvae and 157 nymphs) was found on 31 of 235 captured lizards (13.2%). The tick infestation is relatively low compared to that of mammals and passerine birds from the same area (Siński et al. 2006, Gryczyńska et al. 2002). Tick infestation depended on the month of capture, being the highest in spring. In autumn no ticks were recorded on any of the captured lizards. The oldest lizards carried the highest number of ticks but no differences related to sex of the host were found. All the collected ticks were analysed by PCR for the presence of Borrelia burgdorferi sensu lato, the etiological agents of Lyme disease. Spirochetes were detected in 11 out of 233 (4.7%) ticks tested. Genetic analysis confirmed that the spirochetes are members of the Borrelia afzelii, B. garinii and B. burgdorferi sensu stricto genospecies. Mixed infection were not detected. The prevalence of infection was analysed in relation to months of the capture, age and sex of the lizards, but differences were not statistically significant. The obtained results suggest that lizards are probably not B. burgdorferi reservoirs, but further studies are required to confirm this.

Reservoir role of lizard Psammodromus algirus in transmission cycle of Borrelia burgdorferi sensu lato (Spirochaetaceae) in Tunisia

To investigate the reservoir role of the lizard Psammodromus algirus for the Lyme disease spirochete, 199 lizards were trapped from April to October 2003 in El Jouza, northwestern Tunisia. In this site, the infection rate of free-living Ixodes ricinus (L.) by Borrelia was evaluated by immunofluorescence as 34.6% for adult ticks and 12.5% for nymphs. Eighty percent of P. algirus (117/146) captured during this study were infested by I. ricinus, the predominant tick species collected from lizards. The intensity of tick infestation of this host by larvae and nymphs ranged from 0.14 to 7.07 and from 1.5 to 6.58, respectively. These immature stages of I. ricinus were found on lizards in spring and the beginning of summer, with a peak of intensity during June (10.16 immature ticks by lizard). Tissue cultures from lizards and xenodiagnosis with larval I. ricinus were used to assess the infection and the ability, respectively, of infected lizards to transmit Borrelia to naive ticks. Seventeen percent of xenodiagnostic ticks (40/229) acquired B. lusitaniae while feeding on P. algirus. Therefore, we demonstrated the ability of the lizards to sustain Borrelia infection and to infect attached ticks, and we proved that P. algirus is a reservoir host competent to transmit B. lusitaniae.

Hosts and pathogen detection for immature stages of Ixodes ricinus (Acari: Ixodidae) in North-Central Spain

To determine hosts of the immature stages of a southern population of Ixodes ricinus, we trapped rodents and birds in an area of north-central Spain in May-June and August-September of 1998 and 1999. The most frequently trapped rodents were Apodemus sylvaticus (230 specimens) and Clethrionomys glareolus (99), with a larval infestation prevalence of 49% and 81%, respectively (in spring) and 21% and 41% (in summer). C. glareolus was always more heavily parasitized by larvae (mean numbers 19.8 in spring, 3.4 in summer) than A. sylvaticus (6.1 and 1.2, respectively). No nymphs were collected from the rodents. The larval distribution pattern differed considerably between rodent host species but not according to the season of the year. The most commonly trapped birds were members of the Turdidae, which had infestation incidences of about 70% (larvae) and 10% (nymphs) in spring and 20-15% in summer. We also used molecular methods for the identification of reservoir hosts of the larval ticks and of the pathogens they contained, from nymphs collected in the same site in June of 2002 and 2003. The study showed that most of the ticks had fed on birds and few on rodents and ruminants. Pathogens detected in these ticks included Babesia microti, Borrelia garinii, B. valaisiana and B. afzelii. Borrelia afzelii was detected in a tick that had apparently fed on a wild boar.