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All issues Volume 33 (2026) Parasite, 33 (2026) 40 Full HTML
Open Access
Issue
Parasite
Volume 33, 2026
Article Number 40
Number of page(s) 11
DOI https://doi.org/10.1051/parasite/2026043
Published online 29 July 2026

© J. Stynen et al., published by EDP Sciences, 2026

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Introduction

Climate change and land-use transitions, including forest fragmentation, have favored tick expansion in recent decades, increasing the risk of tick bites and tick-borne diseases (TBDs) such as Lyme borreliosis, particularly in the northern hemisphere [4, 15]. In Europe, populations of Ixodes ricinus have expanded across a variety of ecosystems as a result of reforestation, increasing urban greening, and the growing abundance of wildlife associated with changes in hunting practices [29, 42, 45]. Consequently, the risk of human TBDs is increasing in urban and suburban environments [53]. A recent review covering 24 European countries reported a mean density of I. ricinus in urban green spaces of 6.9 (range 0.1–28.8) ticks per 100 m2, with a mean Borrelia prevalence of 17.3% (range 3.1–38.1%) [23]. Although urban greening of cities is promoted to mitigate global warming, improve human well-being, and provide recreational opportunities, it may also increase acarological risk [18].

In France, only a few studies have investigated ticks in suburban forests near Paris [37, 38] and within the city of Lyon across different urban ecosystems [40, 49]. In the Lyon region, the prevalence of B. burgdorferi s.l. in Ixodes ticks was 13.2% [49], and ticks were found to be scarce in urban parks but abundant in peri-urban forests [40]. Previously, we assessed the impact of anthropization on ticks and TBDs across different ecosystems in Strasbourg [7], a city located in eastern France, in a region highly endemic for ticks and TBDs such as Lyme borreliosis, tick-borne encephalitis [58, 69], and anaplasmosis [35]. That study revealed a potential environmental hazard associated with TBDs in certain urban ecosystems, including the Orangerie park and a golf course, due to the presence of several Borrelia burgdorferi genospecies and Borrelia miyamotoi, the causative agent of relapsing fever [7].

Ixodes ricinus is the most important tick species in Europe and is particularly abundant in deciduous and mixed forests. High relative humidity, maintained by leaf litter and forest canopy cover, is essential for its survival [20]. The lifecycle of I. ricinus occurs predominantly in vegetation, with only a small proportion of time devoted to blood feeding on a wide range of mammals, birds, and reptiles [20]. Following oviposition by engorged females, ticks develop through three life stages: larva, nymph, and adult male or female. Ixodes ricinus is a generalist ectoparasite [28]. Larvae generally feed on small vertebrates such as wood mice (Apodemus sylvaticus) and bank voles (Myodes glareolus), whereas nymphs parasitize a broader range of hosts, including birds, medium-sized mammals (e.g., hedgehogs, foxes, and hares), and roe deer (Capreolus capreolus). Adult females typically feed on large mammals such as deer [33]. Deer play a crucial role in maintaining tick populations [13, 19, 45]; however, alternative hosts such as foxes and hedgehogs may also be fed upon by female ticks in urban parks [20, 70]. In addition, birds contribute to the dispersal of ticks across landscapes [27, 72]. Humans are accidental hosts and are usually exposed when entering habitats where ticks occur, such as wooded or grassy areas.

Among the microorganisms potentially transmitted by I. ricinus, Borrelia burgdorferi sensu lato (s.l.) is the most important because it is the causative agent of Lyme borreliosis [4, 64]. Other bacterial pathogens transmitted by I. ricinus include Anaplasma phagocytophilum and Neoehrlichia mikurensis [30, 60]. TBDs are zoonoses involving a variety of vertebrate hosts that participate in pathogen maintenance and transmission [4]. For B. burgdorferi s.l., the principal reservoir hosts are rodents (e.g., mice, voles, and shrews) and birds (e.g., blackbirds and great tits). Roe deer, not a reservoir-competent for Borrelia [20], constitute an important reservoir host for Anaplasma [16] and Babesia venatorum (formerly Babesia EU1) [2]. However, a recent study based on the analysis of remnant blood meals in ticks from urban and forested areas in Finland demonstrated that host importance differs between ecosystem types. In particular, squirrels, leporids [62], and blackbirds [70] appear to be more important hosts in urban environments, whereas roe deer and voles play a more prominent role in forest ecosystems [62].

In the present study, we sampled ticks along an urbanization gradient extending from north to south across Strasbourg. Eight sites were selected, including the university’s botanical garden and several urban parks and peri-urban forests. During the peak period of tick activity, from March to June 2024, we investigated the abundance of questing ticks and the occurrence of three tick-borne bacterial pathogens: B. burgdorferi s.l., A. phagocytophilum, and N. mikurensis. These pathogens are known to occur in eastern France and are responsible for human clinical cases [6, 35, 58]. The main objective of this study was to assess variations in the density of nymphs (DON), density of infected nymphs (DIN), and nymphal infection prevalence (NIP) for the three potentially pathogenic microorganisms along the urbanization gradient and throughout the sampling period.

Materials and methods

Study area, sampling sites, and tick collection

Eight urban and peri-urban sites in Strasbourg, eastern France, were sampled monthly in 2024 (GPS coordinates: 48.5734, 7.7521). Strasbourg has a population of approximately 272,100 and covers an area of 78.26 km2. Its altitude ranges from 132 m to 151 m above sea level. The city is surrounded by alluvial forests that have undergone various sylvatic management practices but still contain old-growth stands and areas that have remained unmanaged since 1984. Study sites 1 and 8 were alluvial forests; site 7 was an ancient alluvial forest; and the remaining sites were urban parks, except for site 4, which was a fenced botanical garden belonging to the university (Fig. 1). All the sites are regularly visited by both professionals and the public for recreational and educational activities.

Thumbnail: Figure 1 Refer to the following caption and surrounding text. Figure 1

Tick collection sites along the urban gradient of Strasbourg. Total collected nymphs: 880. Total tested nymphs: 657. Red numbers correspond to collected ticks. Green rectangles indicate alluvial forests.

The ticks were collected without handling any vertebrates. Questing ticks were sampled during the peak activity period (March to June 2024) by dragging a 1 m2 white cloth over the vegetation along a 300 m2 transect at each study site. The cloth was inspected every 10 m2, and successive 10-m2 transects were separated by 20–30 m to ensure random sampling. Ticks (adults and nymphs) were collected using tweezers, transferred alive into collection tubes, transported to the laboratory, and stored at −20 °C until analysis. At each site, the thirty 10-m2 transects were grouped into three 100-m2 sections for subsequent analyses.

DNA extraction and detection of bacterial pathogens by PCR

Up to 60 nymphs per site were randomly selected and analyzed individually. DNA was extracted using the ammonium hydroxide–based method [21, 52]. To detect B. burgdorferi s.l. DNA, an initial amplification via real-time PCR was performed to target the conserved region of the flagellin B gene, using one primer pair and two Taqman® probes. Amplification and data analysis were carried out using a CFX OPUS96 BIORAD Instrument.

For Borrelia genotyping, a second real-time PCR typing assay was performed on all positive samples to identify B. burgdorferi s.l. genospecies, using the same primers together with species-specific fluorescent hybridization probes (10 FRET probes and one TaqMan® probe). These probes specifically target B. burgdorferi s.s., B. garinii/B. bavariensis, B. afzelii, B. valaisiana, and B. lusitaniae. Following amplification, the PCR products were subjected to a gradual increase in temperature, and the melting temperature (Tm) of each PCR product/FRET probe duplex was determined. For each genospecies and its probe, the Tm was specific and enabled species identification [7].

For A. phagocytophilum, the major surface protein 4 (msp4) gene was targeted [35]. For N. mikurensis, a previously described RT-qPCR assay targeting the GroEl gene was used [31]. Positive controls (5 μL B. japonica DNA; 5 μL of DNA from tick positive for Anaplasma or B. miyamotoi) and negative controls (reagents with 5 μL of H2O instead of DNA) were included in each PCR run to verify the reaction specificity and detect potential contamination. All PCR assays were performed using a BioRad Opus 384 System.

MALDI-ToF-MS for tick species identification

Collected ticks were identified by matrix-assisted laser desorption–ionization time-of-flight mass spectrometry (MALDI-TOF-MS) [8]. Briefly, four legs from each adult or nymph tick were analyzed using the same protocol and settings as previously described [5]. A log score value of at least 1.8 was required for reliable species identification, with a minimum difference of 0.2 between the highest and second-highest species match scores.

Statistical analysis

To assess the risk of acquiring TBDs, we first determined the density of nymphs per 100 m2 (DON) and then the nymphal infection prevalence (NIP). We then calculated the density of infected nymphs per 100 m2 (DIN) by multiplying DON by NIP, thereby estimating the acarological hazard [25].

Statistical analyses were performed using R software (version 4.2.1) to investigate spatial and temporal variations in nymph density and infection prevalence, and to identify ecosystems exhibiting differences in DON, DIN, and NIP. The experimental design was a nested experiment with three nested factors: sites (eight levels), months (four levels), and replicates (three levels). The non-parametric Friedman test with months (sites) treated as blocks, was used to assess significant differences in DON and DIN among the eight sites and across the four sampling months. Kendall’s rank correlation coefficient was used to evaluate the monotonic relationship between the numbers of infected and tested nymphs. Fisher’s exact test was applied to compare nymphal infection prevalence across sites and months, as well as the relative proportions of the three potentially pathogenic microorganisms among infected nymphs according to site and month.

Generalized linear models (GLMs) were also considered to examine the effects of site and month on DON, DIN, and NIP. DON and DIN were modeled using negative binomial regression with a log-linear link function, whereas NIP was modeled using logistic regression. Separate models were fitted for each pathogen and for all pathogens combined, with site and month included as explanatory variables. Both the non-parametric analyses and the GLMs yielded consistent results. To avoid unnecessary redundancy, we chose to present only the results of the non-parametric analyses in the main text.

This decision was motivated by the characteristics of the dataset, namely the relatively small sample size and the absence of ecological and environmental covariates. Of note, fitting GLMs that include both site and month as explanatory variables may be ambitious given the limited number of observations. Furthermore, models of this kind would be more informative if they incorporated environmental variables known to influence tick abundance such as vegetation type, humidity, and temperature, particularly because sampling conditions may vary substantially among sampling dates. In addition, non-parametric methods, which are characterized by their statistical robustness, perhaps better reflect the scope of this work and are, in fact, largely sufficient to address our research objectives. However, the results of the GLMs are provided in the Supplementary material (Supplementary File 3).

Results

Density of Ixodes nymphs (DON) across different sites according to ecosystem

A total of 880 ticks were collected over four months in 2024 from eight sites in and around Strasbourg with varying urbanization levels (Supplementary Table S1). Mass spectrometry was used to identify the ticks, as this technique is now a reliable method for identifying different arthropod vectors at the species level [5, 59]. It revealed that 87.3% of randomly tested ticks were I. ricinus, and 12.7% were Ixodes frontalis. Ixodes frontalis was primarily detected in the botanical garden around a bamboo plantation, accounting for 63.6% of ticks collected there. At the remaining sites, only 3.3% of collected ticks were I. frontalis (data not shown).

Density of nymph (DON) varied by site and month (Table 1). Statistical analysis revealed varying DONs across the eight sites (Friedman test, p < 0.02), regardless of the value given to the missing datum (botanical garden, March).

Table 1

Density of nymph (DON) per 100 m2 for different sites from March to June 2024.

The “site” effect showed that DON was lowest in the city center (mean DON ranging from 0.08/100 m2 to 2.00/100 m2; SD = 0.17 and 2.94, respectively), whereas it rapidly increased with increasing distance from densely built-up urban areas, both to the north (Pourtalès park: mean = 6.58; SD = 7.09; Robertsau forest: mean = 24.75; SD = 19.50) and the south (Neudorf forest: mean = 18.25; SD = 7.60; Rohrschollen forest: mean = 20.5; SD = 16.47) (Table 1).

Three distinct zones were identified based on nymph abundance: northern sites: Robertsau forest and Pourtalès park, central urban sites: Orangerie park, botanical garden, Citadelle park, and Schulmeister park, and southern sites: Neudorf and Rohrschollen forests. No significant differences in DON were observed among the four months (Friedman test, p > 0.90), although the highest DON was recorded in May 2024 in Robertsau forest (51.67/100 m2; SD = 6.66) (Table 1).

Nymphal infection prevalence (NIP)

We observed a strong monotonic relationship between the numbers of infected and analyzed nymphs (Kendall’s τ = 0.794, p < 10−4) (Supplementary Figure S1). The overall NIP was estimated at 27.7% (95% CI: 24.3–31.3). The NIP values significantly differed across the eight sites (Fisher’s exact test, p = 0.003) and the three zones (p = 0.022) (Figs. 2A and 2B). In the north, NIP was significantly higher in Robertsau forest (36.4%; 95% CI: 29.5–43.9, 67/184) than in Pourtalès park (15.2%; 95% CI: 8.4–25.4, 12/79) (Supplementary Table S2a). Furthermore, the NIP was lower in city parks (10.3%; 95% CI: 4.1–23.6, 4/39) than in alluvial forests. In addition, the NIP in the alluvial forests of the northern sites (30.0%; 95% CI: 24.8–35.8, 79/263) and the southern sites (27.9%; 95% CI: 23.5–32.8, 99/355) was comparable (Supplementary Table S2b). The NIP varied significantly across the four months (p < 0.001), with the highest being in May (40.4%; 95% CI: 32.3–49.0, 57/141) and the lowest being in April (16.8%; 95% CI: 11.7–23.4, 29/173) (Supplementary Table S2c).

Thumbnail: Figure 2 Refer to the following caption and surrounding text. Figure 2

(A) Number of infected and uninfected nymphs at different sites, (B) within the three zones (ecosystems): north, city, and south, (C) over the course of the months.

The prevalence of the three potentially pathogenic microorganisms, B. burgdorferi s.l., A. phagocytophilum, and N. mikurensis was determined (Table 2). Among the 657 nymphs analyzed, 182 were infected (27.7%; 95% CI: 24.3–31.3). Because 31 nymphs were co-infected (4.7%; 95% CI: 3.2–6.7, 31/657), a total of 214 infections were recorded. Co-infections consisted of 26 cases involving B. afzelii and N. mikurensis, four involving B. burgdorferi s.l. and A. phagocytophilum, and one triple co-infection involving all three microorganisms (Robertsau forest, May 2024).

Table 2

Bacterial prevalence on the Ixodes ricinus nymphs.

The relative proportions of the three bacteria in infected nymphs varied across sites (p < 0.001), zones (p < 10−4), and months (p = 0.006) (Fig. 3 and Supplementary Table S3). The proportion of B. burgdorferi s.l. was low at the northern sites (44.0%; 95% CI: 34.2–54.3, 44/100) and high at the southern sites (72.7%; 95% CI: 63.3–80.6, 80/110). Neoehrlichia mikurensis showed the opposite trend (north: 52.0%; 95% CI: 41.8–62.0, 52/100; south: 22.7%; 95% CI: 15.5–31.9, 25/110). The proportion of A. phagocytophilum in infected nymphs was relatively high in April (14.7%, 95% CI: 5.5–31.8, 5/34).

Thumbnail: Figure 3 Refer to the following caption and surrounding text. Figure 3

Abundance of the three potentially pathogenic bacteria in infected nymphs, (A) across the three areas (ecosystems) – namely north, city, and south, and (B) over the course of several months. Abbreviations: BOR, Borrelia burgdorferi sensu lato; ANA, Anaplasma phagocytophilum, and NEH, Neoehrlichia mikurensis.

Acarological hazard and presence of Borrelia genospecies in ecosystems

The acarological risk was defined as the likelihood of encountering infected ticks in a given area. This risk was quantified using the DON and NIP. It refers to the density of infected nymphs (DIN). Since we had no data on human exposure, we used the term “acarological hazard”. DIN varied among sites and sampling months (Table 3). Significant differences in DIN were observed among the eight sites (Friedman test, p < 0.01), whereas no significant differences were detected among the four sampling months (p > 0.40). The highest DIN was recorded in May in Robertsau alluvial forest (28.42 infected nymphs/100 m2) (Table 3). Mean DIN values were highest in the alluvial forests located north and south of Strasbourg (Robertsau: 10.21; Neudorf: 4.93; Rohrschollen: 5.88). No infected ticks were detected in city parks (Citadelle and Schulmeister). In Orangerie park, only three ticks infected with Borrelia were detected, whereas a single tick infected with A. phagocytophilum was found in the botanical garden during the study period (Supplementary Table S3a).

Table 3

Density of the infected nymphs (DIN)/100 m2 at different sites from March 2024 to June 2024.

Borrelia burgdorferi s.l. is the most important pathogen for humans in the northern temperate zones [65], particularly in France [57]. We identified human-pathogenic Borrelia genospecies. Borrelia afzelii was the most represented genospecies at all sites (52%), except in the city center (Citadelle, Schulmeister, and botanical garden), followed by the bird-associated species such as B. garinii (13%) and B. valaisiana (19%) (Fig. 4). Notably, a significant number of ticks infected with B. lusitaniae (8%) was detected in Rohrschollen forest. Borrelia species exhibited co-infection with other microorganisms at a rate of 4.7%. The most frequent association was N. mikurensis–B. burgdorferi s.l. (Table 2).

Thumbnail: Figure 4 Refer to the following caption and surrounding text. Figure 4

(A) B. burgdorferi sensu lato infection prevalence per site in 2024, (B) overall prevalence of B. burgdorferi s.l. (Bbsl) species in 2024. Bbss: Borrelia burgdorferi sensu stricto. 1, 7, 8: alluvial forests; 2, 3: city parks with connectivity to a forest; 4, 5, 6: city parks and botanical garden.

Overall, no significant temporal variation in DON and DIN was observed during the four-month sampling period (Friedman test, p > 0.90 and p > 0.40, respectively). These statistical results may appear inconsistent with the data presented in Tables 1 and 3, which show noticeable month-to-month differences in the mean values of DON and DIN. This apparent discrepancy can be explained both by the high variability among sites and the limited statistical power of the Friedman test.

Discussion

The spread of Ixodes ticks in rural ecosystems has raised concerns about their increasing prevalence in urban and peri-urban areas across Europe. While urban greening, promoted to combat climate change and improve human well-being, creates novel ecosystems that favor ticks; it also increases the risk of tick-borne diseases (TBDs) for urban residents [15, 26, 67]. Additionally, efforts to enhance biodiversity through urban greening, the protection of certain natural areas, and changes in forestry practices are promoting connectivity between the ecosystems and the movement of wildlife.

The Strasbourg region, located in the Alsace Plain, has undergone significant landscape changes in recent decades, shifting from mixed cropping to maize monoculture, which has led to landscape fragmentation. The city of Strasbourg, named French Capital of Biodiversity in 2014 under the theme “Urban Agriculture and Biodiversity”, has preserved numerous natural areas, including three Natura 2000 sites, and manages 430 ha of green spaces. Its local climate plan includes 13 objectives, such as developing a green belt as a plant shield. This study was conducted as part of the European URBACT project (Strasbourg, “One Health 4 Cities”), which aims to revitalize a small watercourse connected to the Rhine River system and raise awareness among local residents.

A previous survey in Strasbourg (2018–2019) revealed that certain parks and peri-urban forested areas were highly conducive to Ixodes and Dermacentor tick populations [1, 7]. The present study highlights that alluvial forests around Strasbourg are also highly favorable ecosystems for these ticks. We focused on Ixodes nymphs, as they are the most common life stage found biting humans [34]. In this study, Ixodes nymphs were significantly infected with B. burgdorferi s.l. (19.3%), A. phagocytophilum (1.5%), and N. mikurensis (11.7%). The abundance of wildlife in Strasbourg enables the circulation of these bacteria, whose primary reservoirs are forest rodents [31, 62] and birds [74], as well as squirrels and shrews in urban areas [62]. Parks in central Strasbourg had few ticks. Tick presence in these ecosystems is likely due to specimens introduced by birds, particularly blackbirds (Turdus merula), as not all developmental stages were collected [14]. The DIN was zero in two city parks, Citadelle and Schulmeister, likely due to poor understory vegetation and an unfavorable ground microclimate for Ixodes ticks and their host community [45]. There is no connectivity between these parks and alluvial forests, a factor known to promote tick presence in cities via the movement of vertebrate hosts [26, 67], creating a metaecosystem [17]. The NIP in alluvial forests (30%) was higher than in central Europe (16.7%) [66]. In other studies conducted in eastern France, lower mean B. burgdorferi s.l. infection rates were detected, with NIPs of 12.5% in Moselle and 9.8% in Argonne region [3, 22], both rural areas. The NIP for N. mikurensis in Strasbourg (11.7%) was similar to that in Argonne (11.2%). The absence of this bacterium in the city suggests that its preferred reservoirs (mice and voles) are not present [31].

Regarding Borrelia genospecies, the most abundant species were B. afzelii, B. valaisiana, B. garinii, B. lusitaniae, and B. burgdorferi s.s. in descending order. In Europe, B. afzelii, whose reservoirs include mice, shrews, and squirrels [62], is generally the most abundant, followed by bird-associated species B. garinii and B. valaisiana [66]. Borrelia afzelii, B. garinii, and B. burgdorferi s.s. are well-known human pathogens and primarily responsible for Lyme disease in Europe and North America [65]. Notably, B. lusitaniae, associated with lizards [44, 74], was detected in Rohrschollen forest. This species is considered a rare or potential cause of Lyme borreliosis [12, 68], with less typical clinical manifestations. Its presence is increasingly documented in other European regions [9, 10].

Bacterial co-infection in Ixodes nymphs was 4.7%. In a three-year study in a forest near Paris, a prevalence of 1.3% was observed after testing for 31 pathogens [37]. The most common co-infection was N. mikurensis with B. afzelii, which has also been observed elsewhere in Europe [36]. Rodents (Myodes, Apodemus, or Microtus) are suspected as the main hosts for this association [11]. Anaplasma phagocytophilum was associated with B. garinii and B. valaisiana, both of which are commonly linked to birds. Blackbirds (Turdus merula) are good reservoirs for these pathogens in urban ecosystems [70, 73]. The acarological risk in Strasbourg and the Alsace region cannot be overlooked, as human cases of TBDs are regularly reported, including anaplasmosis [35], neoehrlichiosis [6], babesiosis [39], and tick-borne encephalitis [69]. Screening for the tick-borne encephalitis virus in ticks would be particularly worthwhile at this time. Interestingly, the first human case was reported in 1968 in Strasbourg [69]. A study conducted from 1970 to 1974 on ticks and rodents revealed that the virus was circulating in the Neudorf Forest (site 7 of the present study) [47]. France made the disease a notifiable disease in 2021 and has noted a resurgence of cases throughout the Grand-Est region [56].

We did not survey private gardens, which may be important at-risk environments for tick bites and TBDs [43, 51, 54]. However, we assessed one community garden and found no ticks. Private gardens in the Netherlands [43], Belgium [54], and Germany [51] have been studied for potential acarological risks. Depending on their location, these gardens may promote tick development if near forests, with abundant leaf litter, hedges, composting areas, and certain hosts [41]. Among the tick species identified in these studies, I. ricinus, a generalist tick that feeds on more than 300 host species [28], was the most abundant, followed by I. frontalis, which shows a strong preference for birds [48] and I. hexagonus which uses hedgehogs as hosts [54]. In this study, we collected mainly I. ricinus ticks, and very few I. frontalis ticks in the botanical garden and a few in the alluvial forests.

In France, few studies have focused on the risk of ticks and associated pathogens in urban and peri-urban ecosystems [37, 38, 40, 50, 71]. Several European studies have investigated tick presence in cities [9, 14, 24, 32, 40, 55, 61], and the detection of potentially pathogenic microorganisms in these ticks has highlighted a potential acarological risk [9, 32, 46, 53, 61]. Vegetation and woodland restorations aim to limit climate change and promote biodiversity and human well-being in urban ecosystems [45]. However, these changes in land use, especially in TBD-endemic areas, increasingly expose communities to previously unknown risks. The presence of diverse hosts in cities allows the development and survival of Ixodes ticks, especially in parks connected to forested ecosystems.

It is crucial to inform local municipalities about the need for ecosystem management and to propose preventive measures for professionals and the public [18]. Concerted actions are needed, including control strategies targeting wildlife, ecosystem management, prevention measures, public awareness campaigns, and accurate medical settings for diagnosing TBDs [4, 63]. Although limited to Strasbourg and one season, this study provides a detailed overview of the spatial distribution of the tick-borne disease hazard in a city located within a region highly endemic for TBDs.

Acknowledgments

We thank the URBACT project community managed by the Eurométropole de Strasbourg (Pascale Rouillard-Neau, Marie Parris, Eliabel Seys), the Zone Atelier Urbaine de Strasbourg – ZAEU (Sandrine Glatron), Espaces Naturels de Strasbourg, the wildlife association “GEMAP,” and Frédéric Tournay for access to the botanical garden.

Funding

This project was funded by Agence Régionale de Santé-Grand Est (ARS-Grand Est N°202312139).

Conflicts of interest

The authors declare that they have no competing interests.

Data availability statement

All data and materials are available upon request.

Author contribution statement

JS, LV, and CB performed PCR analyses; NB and JS conducted fieldwork; NB and AM wrote the manuscript and analyzed the data.

Supplementary material

Supplementary File 1: Study sites. Access Supplementary Material

Supplementary File 2: Animals present at the various sites according to GEPMA (Groupe d’Étude et de Protection des Mammifères d’Alsace). Access Supplementary Material

Supplementary File 3: Regression analyses

Generalized linear models (GLMs). Negative binomial regression for nymphal abundance (DON). Logistic regression for nymphal infection prevalence (NIP).

Access Supplementary Material

Supplementary Table S1: Number of Ixodes ricinus nymphs collected at the sites from March to June 2024. Counts for each triplicate and total per site and month. Access Supplementary Material

Thumbnail: Figure 5 Refer to the following caption and surrounding text. Figure 5

Supplementary Figure S1: Infected nymphs versus analyzed nymphs within the three zones (ecosystems) examined.

Supplementary Table S2: Nymphal infection prevalence (NIP). Table S2a: Nymphal infection prevalence (NIP) for the 8 sites. Table S2b: Nymphal infection prevalence (NIP) for the 3 zones (ecosystems). Table S2c: Nymphal infection prevalence (NIP) for the 4 months. Access Supplementary Material

Supplementary Table S3: Bacterial pathogens. Tested bacteria: BOR: Borrelia burgdorferi sensu lato, ANA: Anaplasma phagocytophilum, NEH: Neoehrlichia mikurensis. Table S3a: Pathogen abundance for each bacterium versus sites. Table S3b: Bacteria abundance versus zones (after grouping of sites). Table S3c: Bacteria abundance versus months. Access Supplementary Material

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Cite this article as: Stynen J, Barthel C, Maul A, Villeneuve L & Boulanger N. 2026. Environmental hazard of tick-borne diseases in urban and peri-urban sites in an endemic area of eastern France. Parasite 33, 40. https://doi.org/10.1051/parasite/2026043.

All Tables

Table 1

Density of nymph (DON) per 100 m2 for different sites from March to June 2024.

In the text
Table 2

Bacterial prevalence on the Ixodes ricinus nymphs.

In the text
Table 3

Density of the infected nymphs (DIN)/100 m2 at different sites from March 2024 to June 2024.

In the text

All Figures

Thumbnail: Figure 1 Refer to the following caption and surrounding text. Figure 1

Tick collection sites along the urban gradient of Strasbourg. Total collected nymphs: 880. Total tested nymphs: 657. Red numbers correspond to collected ticks. Green rectangles indicate alluvial forests.
In the text
Thumbnail: Figure 2 Refer to the following caption and surrounding text. Figure 2

(A) Number of infected and uninfected nymphs at different sites, (B) within the three zones (ecosystems): north, city, and south, (C) over the course of the months.
In the text
Thumbnail: Figure 3 Refer to the following caption and surrounding text. Figure 3

Abundance of the three potentially pathogenic bacteria in infected nymphs, (A) across the three areas (ecosystems) – namely north, city, and south, and (B) over the course of several months. Abbreviations: BOR, Borrelia burgdorferi sensu lato; ANA, Anaplasma phagocytophilum, and NEH, Neoehrlichia mikurensis.
In the text
Thumbnail: Figure 4 Refer to the following caption and surrounding text. Figure 4

(A) B. burgdorferi sensu lato infection prevalence per site in 2024, (B) overall prevalence of B. burgdorferi s.l. (Bbsl) species in 2024. Bbss: Borrelia burgdorferi sensu stricto. 1, 7, 8: alluvial forests; 2, 3: city parks with connectivity to a forest; 4, 5, 6: city parks and botanical garden.
In the text
Thumbnail: Figure 5 Refer to the following caption and surrounding text. Figure 5

Supplementary Figure S1: Infected nymphs versus analyzed nymphs within the three zones (ecosystems) examined.
In the text

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