Introduced Siberian chipmunks are more heavily infested by ixodid ticks than are native bank voles in a suburban forest in France

An invasive human commensal and a native marsupial maintain tick populations at the urban fringe

Ticks (Acari: Ixodidae) are major disease vectors globally making it increasingly important to understand how altered vertebrate communities in urban areas shape tick population dynamics. In urban landscapes of Australia, little is known about which native and introduced small mammals maintain tick populations preventing host-targeted tick management and leading to human-wildlife conflict. Here, we determined (1) larval, nymphal, and adult tick burdens on host species and potential drivers, (2) the number of ticks supported by the different host populations, and (3) the proportion of medically significant tick species feeding on the different host species in Northern Sydney. We counted 3551 ticks on 241 mammals at 15 sites and found that long-nosed bandicoots (Perameles nasuta) hosted more ticks of all life stages than other small mammals but introduced black rats (Rattus rattus) were more abundant at most sites (33%-100%) and therefore important in supporting larval and nymphal ticks in our study areas. Black rats and bandicoots hosted a greater proportion of medically significant tick species including Ixodes holocyclus than other hosts. Our results show that an introduced human commensal contributes to maintaining urban tick populations and suggests ticks could be managed by controlling rat populations on urban fringes.

The Eurasian shrew and vole tick Ixodes trianguliceps: geographical distribution, climate preference, and pathogens detected

The Eurasian shrew and vole tick Ixodes trianguliceps Birula lives in the nests and burrows of its small mammalian hosts and is-along with larvae and nymphs of Ixodes ricinus or Ixodes persulcatus-one of the most commonly collected tick species from these hosts in its Eurasian range. Ixodes trianguliceps is a proven vector of Babesia microti. In this study, up-to-date maps depicting the geographical distribution and the climate preference of I. trianguliceps are presented. A dataset was compiled, resulting in 1161 georeferenced locations in Eurasia. This data set covers the entire range of I. trianguliceps for the first time. The distribution area between 8[Formula: see text] W-105[Formula: see text] E and 40-69[Formula: see text] N extends from Northern Spain to Western Siberia. To investigate the climate adaptation of I. trianguliceps, the georeferenced locations were superimposed on a high-resolution map of the Köppen-Geiger climate classification. The Köppen profile for I. trianguliceps, i.e., a frequency distribution of the tick occurrence under different climates, shows two peaks related to the following climates: warm temperate with precipitation all year round (Cfb), and boreal with warm or cold summers and precipitation all year round (Dfb, Dfc). Almost 97% of all known I. trianguliceps locations are related to these climates. Thus, I. trianguliceps prefers climates with warm or cold summers without dry periods. Cold winters do not limit the distribution of this nidicolous tick species, which has been recorded in the European Alps and the Caucasus Mountains up to altitudes of 2400 m. Conversely, I. trianguliceps does not occur in the Mediterranean area with its hot and dry summers.

Research effort on birds' reservoir host potential for Lyme borreliosis: A systematic review and perspectives

Zoonotic tick-borne diseases threat human and animal health. Understanding the role of hosts in the production of infected ticks in an epidemiological system is essential to be able to design effective measures to reduce the exposure of humans and animals to infectious tick bites. The reservoir host potential, that is, number of infected ticks produced by a host species, depends on three components: tick production, realized reservoir competence and host density. The parameters and factors that determine the reservoir host potential need to be characterized to achieve a robust understanding of the dynamics of pathogen-tick-host systems, and thus to mitigate the acarological risk of emerging infections. Few studies have investigated the role of birds in the local spread of Lyme borreliosis Borrelia. Knowledge of the research effort on the reservoir host potential of birds in Lyme borreliosis Borrelia circulation is necessary to prioritize future research on this topic. We provide a systematic review of the research effort on components of the reservoir host potential of wild birds for Lyme borreliosis Borrelia circulation, and factors that modulate these components in the European epidemiological system. Our review of 242 selected publications showed that tick production has been 1.4 and 21 times more studied than realized reservoir competence and bird density respectively. Only one study achieved to characterize the global host reservoir potential of birds in a given epidemiological system. Investigated factors were mostly related to bird species identity, individual characteristics of birds and tick characteristics, whereas the influence of bird life-history traits have been largely under-investigated. Because simultaneous characterization of all parameters is notoriously complex, interdisciplinary research is needed to combine and accumulate independent field and laboratory investigations targeting each parameter on specific epidemiological system or host species. This can help gain an integrated appraisal of the functioning of the studied system at a local scale.

Invasive rabbits host immature Ixodes ticks at the urban-forest interface

Introduced wildlife may be important alternative hosts for generalist ticks that cause health issues for humans and companion animals in urban areas, but to date are rarely considered as part of the tick-host community compared to native wildlife. In Australia, European rabbits, Oryctolagus cuniculus, are a widespread and abundant invasive species common to a range of human-modified ecosystems. To understand the potential role of rabbits in the life cycle of Australian ticks, we investigated the seasonal abundance of all tick life stages (larva, nymph, and adult) on rabbits collected from pest control programs in two urban forest remnants in Sydney, Australia. We also recorded whether larvae, nymphs, and adults were attached to the head, body, or limbs of rabbits to reveal patterns of tick attachment. Of the 2426 Ixodes ticks collected from 42 rabbits, larvae were by far the most abundant life stage (2360), peaking in abundance in autumn, while small numbers of nymphs (62) and adults (4) were present in winter and summer respectively. Larvae were found all over the body, whereas adults and nymphs were predominantly attached to the head, suggesting that the mature life stages use the host landscape differently, or that adults or nymphs may be groomed off the body. The most abundant tick species, as determined by morphology and DNA sequencing, was Ixodes holocyclus, a generalist tick responsible for significant human and companion animal health concerns in Australia. Our findings highlight the importance of understanding the role of introduced wildlife in tick dynamics particularly in novel ecosystems where non-native hosts may be more abundant than native hosts.

Arthropods and associated pathogens from native and introduced rodents in Northeastern Italy

Introduced Siberian chipmunks Eutamias sibiricus have been reported to be important reservoirs for human Lyme disease, as they may host high numbers of hard ticks carrying Borrelia spp. and other pathogens. In the present study, we assessed the prevalence of Borrelia spp. and other pathogenic bacteria in ectoparasite arthropod species infesting Siberian chipmunks and coexisting native small rodents. Small rodents were trapped with Sherman traps in Veneto (NE Italy), where the largest Italian populations of chipmunks occur. A total of 14 individual ticks were found on 223 rodents, with 6 more ticks obtained from stored dead chipmunks from the same study area. Ectoparasites were screened for pathogens by molecular analyses including species-specific PCR amplifications. Rickettsia monacensis, Borrelia lusitaniae, and Anaplasma platys were present in the parasites of both native rodents and introduced chipmunks. The present findings suggest a role for the invasive species E. sibiricus in the maintenance of the Ixodes ricinus life cycle, which may result in the modification of the transmission dynamics of tick-borne pathogens. Moreover, the presence of Rickettsia in urban populations of chipmunks may represent a serious risk for human health and should be investigated further.

Effects of conservation management of landscapes and vertebrate communities on Lyme borreliosis risk in the United Kingdom

Landscape change and altered host abundance are major drivers of zoonotic pathogen emergence. Conservation and biodiversity management of landscapes and vertebrate communities can have secondary effects on vector-borne pathogen transmission that are important to assess. Here we review the potential implications of these activities on the risk of Lyme borreliosis in the United Kingdom. Conservation management activities include woodland expansion, management and restoration, deer management, urban greening and the release and culling of non-native species. Available evidence suggests that increasing woodland extent, implementing biodiversity policies that encourage ecotonal habitat and urban greening can increase the risk of Lyme borreliosis by increasing suitable habitat for hosts and the tick vectors. However, this can depend on whether deer population management is carried out as part of these conservation activities. Exclusion fencing or culling deer to low densities can decrease tick abundance and Lyme borreliosis risk. As management actions often constitute large-scale perturbation experiments, these hold great potential to understand underlying drivers of tick and pathogen dynamics. We recommend integrating monitoring of ticks and the risk of tick-borne pathogens with conservation management activities. This would help fill knowledge gaps and the production of best practice guidelines to reduce risks.

This article is part of the themed issue ‘Conservation, biodiversity and infectious disease: scientific evidence and policy implications’.

A Borrelia afzelii Infection Increases Larval Tick Burden on Myodes glareolus (Rodentia: Cricetidae) and Nymphal Body Weight of Ixodes ricinus (Acari: Ixodidae)

Several microorganisms have been shown to manipulate their host or vector to enhance their own transmission. Here we examined whether an infection with Borrelia afzelii affects its transmission between its bank vole (Myodes glareolus, Schreber, 1780) host and tick vector. Captive-bred bank voles were inoculated with B. afzelii or control medium, after which host preference of Ixodes ricinus L. nymphs was determined in a Y-tube olfactometer. Thereafter, infected and uninfected bank voles were placed in a semifield arena containing questing larvae to measure larval tick attachment. Engorged larvae were collected from these bank voles, molted into nymphs, weighed, and analyzed for infection by PCR.Nymphs were attracted to the odors of a bank vole compared to ambient air and preferred the odors of an infected bank vole over that of an uninfected bank vole. In the semifield arena, infected male bank voles had greater larval tick burdens then uninfected males, while similar larval tick burdens were observed on females regardless of infection status. Nymphal ticks that acquired a B. afzelii infection had higher body weight than nymphs that did not acquire an infection regardless of the infection status of the vole. These results show that a B. afzelii infection in bank voles increases larval tick burden and that a B. afzelii infection in larvae increases nymphal body weight. This finding provides novel ecological insights into the enzootic cycle of B. afzelii.

Multiple independent transmission cycles of a tick-borne pathogen within a local host community

Many pathogens are maintained by multiple host species and involve multiple strains with potentially different phenotypic characteristics. Disentangling transmission patterns in such systems is often challenging, yet investigating how different host species contribute to transmission is crucial to properly assess and manage disease risk. We aim to reveal transmission cycles of bacteria within the Borrelia burgdorferi species complex, which include Lyme disease agents. We characterized Borrelia genotypes found in 488 infected Ixodes ricinus nymphs collected in the Sénart Forest located near Paris (France). These genotypes were compared to those observed in three sympatric species of small mammals and network analyses reveal four independent transmission cycles. Statistical modelling shows that two cycles involving chipmunks, an introduced species, and non-sampled host species such as birds, are responsible for the majority of tick infections. In contrast, the cycle involving native bank voles only accounts for a small proportion of infected ticks. Genotypes associated with the two primary transmission cycles were isolated from Lyme disease patients, confirming the epidemiological threat posed by these strains. Our work demonstrates that combining high-throughput sequence typing with networks tools and statistical modeling is a promising approach for characterizing transmission cycles of multi-host pathogens in complex ecological settings.

Larvae of Ixodes ricinus transmit Borrelia afzelii and B. miyamotoi to vertebrate hosts

Background

Lyme borreliosis is the most common tick-borne human disease and is caused by Borrelia burgdorferi sensu lato (s.l.). Borrelia miyamotoi, a relapsing fever spirochaete, is transmitted transovarially, whereas this has not been shown for B. burgdorferi (s.l). Therefore, B. burgdorferi (s.l) is considered to cycle from nymphs to larvae through vertebrates. Larvae of Ixodes ricinus are occasionally B. burgdorferi (s.l) infected, but their vector competence has never been studied.

Methods

We challenged 20 laboratory mice with field-collected larvae of I. ricinus. A subset of these larvae was analysed for infections with B. burgdorferi (s.l) and B. miyamotoi. After three to four challenges, mice were sacrificed and skin and spleen samples were analysed for infection by PCR and culture.

Results

Field-collected larvae were naturally infected with B. burgdorferi (s.l) (0.62 %) and B. miyamotoi (2.0 %). Two mice acquired a B. afzelii infection and four mice acquired a B. miyamotoi infection during the larval challenges.

Conclusion

We showed that larvae of I. ricinus transmit B. afzelii and B. miyamotoi to rodents and calculated that rodents have a considerable chance of acquiring infections from larvae compared to nymphs. As a result, B. afzelii can cycle between larvae through rodents. Our findings further imply that larval bites on humans, which easily go unnoticed, can cause Lyme borreliosis and Borrelia miyamotoi disease.

Mapping human risk of infection with Borrelia burgdorferi sensu lato, the agent of Lyme borreliosis, in a periurban forest in France

Lyme borreliosis is a major zoonosis in Europe, with estimates of over 26,000 cases per year in France alone. The etiological agents are spirochete bacteria that belong to the Borrelia burgdorferi sensu lato (s. l.) complex and are transmitted by hard ticks among a large range of vertebrate hosts. In Europe, the tick Ixodes ricinus is the main vector. In the absence of a vaccine and given the current difficulties to diagnose and treat chronic Lyme syndromes, there is urgent need for prevention. In this context, accurate information on the spatial patterns of risk of exposure to ticks is of prime importance for public health. The objective of our study was to provide a snapshot map of the risk of human infection with B. burgdorferi s. l. pathogens in a periurban forest at a high resolution, and to analyze the factors that contribute to variation in this risk. Field monitoring took place over three weeks in May 2011 in the suburban Sénart forest (3,200ha; southeast of Paris), which receives over 3 million people annually. We sampled ticks over the entire forest area (from 220 forest stands with a total area of 35,200m(2)) and quantified the density of questing nymphs (DON), the prevalence of infection among nymphs (NIP), and the density of infected nymphs (DIN), which is the most important predictor of the human risk of Lyme borreliosis. For each of these response variables, we explored the relative roles of weather (saturation deficit), hosts (abundance indices of ungulates and Tamias sibiricus, an introduced rodent species), vegetation and forest cover, superficial soil composition, and the distance to forest roads. In total, 19,546 questing nymphs were collected and the presence of B. burgdorferi s. l. was tested in 3,903 nymphs by qPCR. The mean DON was 5.6 nymphs per 10m(2) (standard deviation=10.4) with an average NIP of 10.1% (standard deviation=0.11). The highest DIN was 8.9 infected nymphs per 10m(2), with a mean of 0.59 (standard deviation=0.6). Our mapping and modeling revealed a strong heterogeneity of risk within the forest. The highest risk was found in the eastern part of the forest and localized patches in the northwestern part. Lyme borreliosis risk was positively associated with stands of deciduous trees (mainly oaks) and roe deer abundance. Contrary to expectations, DIN actually increased with distance from the point of introduction of T. sibiricus (i.e., DIN was higher in areas with potentially lower abundances of T. sibiricus). Thus, despite the fact that T. sibiricus is an important reservoir host for B. burgdorferi s. l., our study found that other explanatory factors played a more important role in determining the density of infected ticks. Precise mapping of the risk of exposure to Lyme borreliosis in a highly visited forest represents an important tool for targeting prevention and control measures, as well as making the general public and local health officials aware of the risks.

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.

An Invasive Mammal (the Gray Squirrel, Sciurus carolinensis) Commonly Hosts Diverse and Atypical Genotypes of the Zoonotic Pathogen Borrelia burgdorferi Sensu Lato

Invasive vertebrate species can act as hosts for endemic pathogens and may alter pathogen community composition and dynamics. For the zoonotic pathogen Borrelia burgdorferisensu lato, the agent of Lyme borreliosis, recent work shows invasive rodent species can be of high epidemiological importance and may support host-specific strains. This study examined the role of gray squirrels (Sciurus carolinensis) (n = 679), an invasive species in the United Kingdom, as B. burgdorferi sensu lato hosts. We found that gray squirrels were frequently infested with Ixodes ricinus, the main vector of B. burgdorferi sensu lato in the United Kingdom, and 11.9% were infected with B. burgdorferi sensu lato. All four genospecies that occur in the United Kingdom were detected in gray squirrels, and unexpectedly, the bird-associated genospecies Borrelia garinii was most common. The second most frequent infection was with Borrelia afzelii. Genotyping of B. garinii and B. afzelii produced no evidence for strains associated with gray squirrels. Generalized linear mixed models (GLMM) identified tick infestation and date of capture as significant factors associated with B. burgdorferi sensu lato infection in gray squirrels, with infection elevated in early summer in squirrels infested with ticks. Invasive gray squirrels appear to become infected with locally circulating strains of B. burgdorferi sensu lato, and further studies are required to determine their role in community disease dynamics. Our findings highlight the fact that the role of introduced host species in B. burgdorferi sensu lato epidemiology can be highly variable and thus difficult to predict.

Infection of Siberian chipmunks (Tamias sibiricus barberi) with Borrelia sp. reveals a low reservoir competence under experimental conditions

Reservoir competence is a key parameter in understanding the role of host species in the epidemiology of multi-host-especially vector-borne-pathogens. With this aim in view, we studied the reservoir competence of the Siberian chipmunk (Tamias sibiricus barberi) recently introduced into Europe, for the multi-host tick-borne bacteria, Borrelia burgdorferi sl, the agent of Lyme borreliosis. T. sibiricus were experimentally exposed to bites from Ixodes ricinus ticks infected with Borrelia burgdorferi sensu stricto and Borrelia afzelii, with subsequent assessment of bacteremia and antibody responses. Borrelia was detected in chipmunk blood samples, ear biopsies and organ necropsies, and in nymphs used for xenodiagnosis (at one and six months after the initial chipmunk infection) via both serological and molecular methods. In total, eight out of twelve chipmunks showed evidence of infection by Borrelia sp., either by ELISA or PCR. Five chipmunks developed an immune response against the bacteria one month after infection. Borrelia infection in at least one organ was observed in seven animals at 14, 38, 93 or 178 days post-infection. Xenodiagnosis was positive for one chipmunk at 38 days, but no longer at 178 days post-infection. Four chipmunks remained uninfected, despite similar infection pressures to those observed in the field. Taken together, these results suggest that chipmunks can be infected through Borrelia-infected tick bites, and can transmit Borrelia to nymphs, but do not remain persistently infected.

Seasonal variation in infestations by ixodids on Siberian chipmunks: effects of host age, sex, and birth season

In mammalian hosts, macroparasite aggregation is highly heterogeneous over space and time and among individuals. While the exact causes of this heterogeneity remain unclear, it has mainly been attributed to individual differences in exposure and susceptibility. Although some extrinsic (e.g., parasite availability) and intrinsic (e.g., sex or age) factors are well known to affect infestation patterns, the joint and possibly interacting effects of these factors are poorly understood. Here, we study the infestation of hard ticks (mainly Ixodes ricinus) in a small rodent, the Siberian chipmunk (Tamias sibiricus), introduced to an oak-hornbeam forest in France. We investigate the seasonal variation in infestation according to the sex, age, birth season (spring-born or summer-born), and body weight of individual hosts while controlling for interannual variability. During the 10-year study period, 3421 tick count events were recorded involving 1017 chipmunks monitored by the capture-mark-recapture procedure. Our results reveal a male-biased parasitism in the Siberian chipmunk, which is not consistent among individuals born in different seasons. This sex bias is observed among spring-born juveniles from July to the beginning of hibernation. For adults, this difference becomes apparent along the reproduction period (May-September) for summer-born adults only. These complex interactions between sex, age, and birth season suggest overall that the seasonal variation of tick load is critically linked to the reproductive behavior of this small ground sciurid.

Ixodes ricinus and Its Transmitted Pathogens in Urban and Peri-Urban Areas in Europe: New Hazards and Relevance for Public Health

Tick-borne diseases represent major public and animal health issues worldwide. Ixodes ricinus, primarily associated with deciduous and mixed forests, is the principal vector of causative agents of viral, bacterial, and protozoan zoonotic diseases in Europe. Recently, abundant tick populations have been observed in European urban green areas, which are of public health relevance due to the exposure of humans and domesticated animals to potentially infected ticks. In urban habitats, small and medium-sized mammals, birds, companion animals (dogs and cats), and larger mammals (roe deer and wild boar) play a role in maintenance of tick populations and as reservoirs of tick-borne pathogens. Presence of ticks infected with tick-borne encephalitis virus and high prevalence of ticks infected with Borrelia burgdorferi s.l., causing Lyme borreliosis, have been reported from urbanized areas in Europe. Emerging pathogens, including bacteria of the order Rickettsiales (Anaplasma phagocytophilum, "Candidatus Neoehrlichia mikurensis," Rickettsia helvetica, and R. monacensis), Borrelia miyamotoi, and protozoans (Babesia divergens, B. venatorum, and B. microti) have also been detected in urban tick populations. Understanding the ecology of ticks and their associations with hosts in a European urbanized environment is crucial to quantify parameters necessary for risk pre-assessment and identification of public health strategies for control and prevention of tick-borne diseases.

Low susceptibility of invasive red lionfish (Pterois volitans) to a generalist ectoparasite in both its introduced and native ranges

Escape from parasites in their native range is one of many mechanisms that can contribute to the success of an invasive species. Gnathiid isopods are blood-feeding ectoparasites that infest a wide range of fish hosts, mostly in coral reef habitats. They are ecologically similar to terrestrial ticks, with the ability to transmit blood-borne parasites and cause damage or even death to heavily infected hosts. Therefore, being highly resistant or highly susceptible to gnathiids can have significant fitness consequences for reef-associated fishes. Indo-Pacific red lionfish (Pterois volitans) have invaded coastal habitats of the western tropical and subtropical Atlantic and Caribbean regions. We assessed the susceptibility of red lionfish to parasitic gnathiid isopods in both their native Pacific and introduced Atlantic ranges via experimental field studies during which lionfish and other, ecologically-similar reef fishes were caged and exposed to gnathiid infestation on shallow coral reefs. Lionfish in both ranges had very few gnathiids when compared with other species, suggesting that lionfish are not highly susceptible to infestation by generalist ectoparasitic gnathiids. While this pattern implies that release from gnathiid infestation is unlikely to contribute to the success of lionfish as invaders, it does suggest that in environments with high gnathiid densities, lionfish may have an advantage over species that are more susceptible to gnathiids. Also, because lionfish are not completely resistant to gnathiids, our results suggest that lionfish could possibly have transported blood parasites between their native Pacific and invaded Atlantic ranges.

High-throughput sequence typing reveals genetic differentiation and host specialization among populations of the Borrelia burgdorferi species complex that infect rodents

Lyme disease is a zoonosis caused by various species belonging to the Borrelia burgdorferi bacterial species complex. These pathogens are transmitted by ticks and infect multiple, taxonomically distinct, host species. From an epidemiological perspective, it is important to determine whether genetic variants within the species complex are able to spread freely through the whole host community or, instead, if certain variants are restricted to particular hosts. To this end, we characterized the genotypes of members of the B. burgdorferi species complex; the bacteria were isolated from more than two hundred individuals captured in the wild and belonging to three different rodent host species. For each individual, we used a high-throughput approach to amplify and sequence rplB, a housekeeping gene, and ospC, which is involved in infection. This approach allowed us to evaluate the genetic diversity both within and among species in the B. burgdorferi species complex. Strong evidence of genetic differentiation among host species was revealed by both genes, even though they are, a priori, not constrained by the same selective pressures. These data are discussed in the context of the advancements made possible by multi-locus high-throughput sequencing and current knowledge of Lyme disease epidemiology.

Ixodes ricinus and Its Transmitted Pathogens in Urban and Peri-Urban Areas in Europe: New Hazards and Relevance for Public Health

Tick-borne diseases represent major public and animal health issues worldwide. Ixodes ricinus, primarily associated with deciduous and mixed forests, is the principal vector of causative agents of viral, bacterial, and protozoan zoonotic diseases in Europe. Recently, abundant tick populations have been observed in European urban green areas, which are of public health relevance due to the exposure of humans and domesticated animals to potentially infected ticks. In urban habitats, small and medium-sized mammals, birds, companion animals (dogs and cats), and larger mammals (roe deer and wild boar) play a role in maintenance of tick populations and as reservoirs of tick-borne pathogens. Presence of ticks infected with tick-borne encephalitis virus and high prevalence of ticks infected with Borrelia burgdorferi s.l., causing Lyme borreliosis, have been reported from urbanized areas in Europe. Emerging pathogens, including bacteria of the order Rickettsiales (Anaplasma phagocytophilum, "Candidatus Neoehrlichia mikurensis," Rickettsia helvetica, and R. monacensis), Borrelia miyamotoi, and protozoans (Babesia divergens, B. venatorum, and B. microti) have also been detected in urban tick populations. Understanding the ecology of ticks and their associations with hosts in a European urbanized environment is crucial to quantify parameters necessary for risk pre-assessment and identification of public health strategies for control and prevention of tick-borne diseases.

Tick pests and vectors (Acari: Ixodoidea) in European towns: Introduction, persistence and management

Ticks have always been a part of fauna in and around human settlements, and their significance changed concurrently with the enlargement of settlements and their transformation into towns. The increased rate of urbanization during the last decades has created a new reality for tick existence. Two groups of ticks are of major concern for modern towns: those living under natural conditions of urban surroundings and those well-adapted to urban conditions. During the process of urbanization, encroachment into forested and uncultivated areas as well as protection of existing green spaces create opportunities for ticks living in nature to also exist under urban and suburban conditions. Conditions of modern urban and especially suburban environment in developed European countries adequately meet tick requirements. Tick species having an advantage in urban areas are those that can use one and the same host at all parasitic stages, can starve for a prolonged time, can use either urban pests or domesticated animals as hosts, and can live in man-made buildings. The ticks of the Argas reflexus group (Argasidae) and the brown dog tick Rhipicephalus sanguineus (Ixodidae) comply with practically all conditions necessary for successful survival in urban areas. The ability of ticks to transmit numerous human and animal pathogens and the presence of many reservoir hosts in urban and suburban areas create persistent danger for human populations and domestic animals. Impact on urban ticks should be directed against the two major requirements of tick existence: reducing populations of potential tick hosts (feral pigeons, stray dogs and cats, and urban rodents), and changing other environmental conditions to make them less suitable for ticks. It is especially important that urban inhabitants be properly informed about the danger posed by ticks, the sites of possible tick attacks, and basic self-protection techniques.

Deciphering bartonella diversity, recombination, and host specificity in a rodent community

Host-specificity is an intrinsic feature of many bacterial pathogens, resulting from a long history of co-adaptation between bacteria and their hosts. Alpha-proteobacteria belonging to the genus Bartonella infect the erythrocytes of a wide range of mammal orders, including rodents. In this study, we performed genetic analysis of Bartonella colonizing a rodent community dominated by bank voles (Myodes glareolus) and wood mice (Apodemus sylvaticus) in a French suburban forest to evaluate their diversity, their capacity to recombine and their level of host specificity. Following the analysis of 550 rodents, we detected 63 distinct genotypes related to B. taylorii, B. grahamii, B. doshiae and a new B. rochalimae-like species. Investigating the most highly represented species, we showed that B. taylorii strain diversity was markedly higher than that of B. grahamii, suggesting a possible severe bottleneck for the latter species. The majority of recovered genotypes presented a strong association with either bank voles or wood mice, with the exception of three B. taylorii genotypes which had a broader host range. Despite the physical barriers created by host specificity, we observed lateral gene transfer between Bartonella genotypes associated with wood mice and Bartonella adapted to bank voles, suggesting that those genotypes might co-habit during their life cycle.

Spatial disaggregation of tick occurrence and ecology at a local scale as a preliminary step for spatial surveillance of tick-borne diseases: general framework and health implications in Belgium

BACKGROUND

The incidence of tick-borne diseases is increasing in Europe. Sub national information on tick distribution, ecology and vector status is often lacking. However, precise location of infection risk can lead to better targeted prevention measures, surveillance and control.

METHODS

In this context, the current paper compiled geolocated tick occurrences in Belgium, a country where tick-borne disease has received little attention, in order to highlight the potential value of spatial approaches and draw some recommendations for future research priorities.

RESULTS

Mapping of 89,289 ticks over 654 sites revealed that ticks such as Ixodes ricinus and Ixodes hexagonus are largely present while Dermacentor reticulatus has a patchy distribution. Suspected hot spots of tick diversity might favor pathogen exchanges and suspected hot spots of I. ricinus abundance might increase human-vector contact locally. This underlines the necessity to map pathogens and ticks in detail. While I. ricinus is the main vector, I. hexagonus is a vector and reservoir of Borrelia burgdorferi s.l., which is active the whole year and is also found in urban settings. This and other nidiculous species bite humans less frequently, but seem to harbour pathogens. Their role in maintaining a pathogenic cycle within the wildlife merits investigation as they might facilitate transmission to humans if co-occurring with I. ricinus. Many micro-organisms are found abroad in tick species present in Belgium. Most have not been recorded locally but have not been searched for. Some are transmitted directly at the time of the bite, suggesting promotion of tick avoidance additionally to tick removal.

CONCLUSION

This countrywide approach to tick-borne diseases has helped delineate recommendations for future research priorities necessary to design public health policies aimed at spatially integrating the major components of the ecological cycle of tick-borne diseases. A systematic survey of tick species and associated pathogens is called for in Europe, as well as better characterisation of species interaction in the ecology of tick-borne diseases, those being all tick species, pathogens, hosts and other species which might play a role in tick-borne diseases complex ecosystems.

Arthropod parasites of the red-bellied squirrel Callosciurus erythraeus introduced into Argentina

The introduction of an exotic species usually modifies parasite-host dynamics by the import of new parasites or the exotic species' acquiral of local parasites. The loss of parasites may determine the outcome of an invasion if the introduced species is liberated from co-evolved parasites in its range of invasion. In addition, an introduced species may pose sanitary risks to humans and other mammals if it serves as a reservoir of pathogens or carries arthropod vectors. The red-bellied squirrel, Callosciurus erythraeus (Pallas) (Rodentia: Sciuridae), was introduced into Argentina in 1970, since when several foci of invasion have been closely associated with humans. Investigation of the parasitological fauna of C. erythraeus in Argentina will generate new information about novel parasite-host dynamics and may provide new insight into the reasons for the successful invasion of this species. The objective of this study was to describe the arthropod parasites of C. erythraeus in Argentina in comparison with previous studies of parasites of this species in its native habitat and in the ranges of its invasion. Occasional host-parasite associations with local arthropod parasites not previously described for C. erythraeus are reported; these include the mites Androlaelaps fahrenholzi (Ewing) (Mesostigmata: Laelapidae) and Ornithonyssus cf. bacoti (Mesostigmata: Macronyssidae), the flea Polygenis (Polygenis) rimatus Jordan (Siphonaptera: Rhopalopsyllidae) and the botfly Cuterebra Clark (Diptera: Oestridae: Cuterebrinae). Cheyletus sp. mites (Trombidiformes: Cheyletidae) were also found. The low prevalence and mean intensity of ectoparasite species may influence invasion dynamics.

Changing distributions of ticks: causes and consequences

Today, we are witnessing changes in the spatial distribution and abundance of many species, including ticks and their associated pathogens. Evidence that these changes are primarily due to climate change, habitat modifications, and the globalisation of human activities are accumulating. Changes in the distribution of ticks and their invasion into new regions can have numerous consequences including modifications in their ecological characteristics and those of endemic species, impacts on the dynamics of local host populations and the emergence of human and livestock disease. Here, we review the principal causes for distributional shifts in tick populations and their consequences in terms of the ecological attributes of the species in question (i.e. phenotypic and genetic responses), pathogen transmission and disease epidemiology. We also describe different methodological approaches currently used to assess and predict such changes and their consequences. We finish with a discussion of new research avenues to develop in order to improve our understanding of these host-vector-pathogen interactions in the context of a changing world.

Introduced Siberian chipmunks (Tamias sibiricus barberi) contribute more to lyme borreliosis risk than native reservoir rodents

The variation of the composition in species of host communities can modify the risk of disease transmission. In particular, the introduction of a new host species can increase health threats by adding a new reservoir and/or by amplifying the circulation of either exotic or native pathogens. Lyme borreliosis is a multi-host vector-borne disease caused by bacteria belonging to the Borrelia burgdorferi sensu lato complex. It is transmitted by the bite of hard ticks, especially Ixodes ricinus in Europe. Previous studies showed that the Siberian chipmunk, Tamias sibiricus barberi, an introduced ground squirrel in the Forest of Sénart (near Paris, France) was highly infested by I. ricinus, and consequently infected by B. burgdorferi sl. An index of the contribution of chipmunks to the density of infected questing nymphs on the vegetation (i.e., the acarological risk for humans) was compared to that of bank voles (Myodes glareolus) and of wood mice (Apodemus sylvaticus), two known native and sympatric competent reservoir hosts. Chipmunks produced nearly 8.5 times more infected questing nymphs than voles and mice. Furthermore, they contribute to a higher diversity of B. burgdorferi sl genospecies (B. afzelii, B. burgdorferi sensu stricto and B. garinii). The contribution of chipmunks varied between years and seasons, according to tick availability. As T. s. barberi must be a competent reservoir, it should amplify B. burgdorferi sl infection, hence increasing the risk of Lyme borreliosis in humans.

Co-infection of Borrelia afzelii and Bartonella spp. in bank voles from a suburban forest

We report the molecular detection of Borrelia afzelii (11%) and Bartonella spp. (56%) in 447 bank voles trapped in a suburban forest in France. Adult voles were infected by significantly more Borrelia afzelii than juveniles (p<0.001), whereas no significant difference was detected in the prevalence of Bartonella spp. between young and adult individuals (p=0.914). Six percent of the animals were co-infected by both bacteria. Analysis of the bank vole carrier status for either pathogen indicated that co-infections occur randomly (p=0.94, CI(95)=[0.53; 1.47]). Sequence analysis revealed that bank voles were infected by a single genotype of Borrelia afzelii and by 32 different Bartonella spp. genotypes, related to three known species specific to rodents (B. taylorii, B. grahamii and B. doshiae) and also two as yet unidentified Bartonella species. Our findings confirm that rodents harbor high levels of potential human pathogens; therefore, widespread surveillance should be undertaken in areas where humans may encounter rodents.

Which forest bird species are the main hosts of the tick, Ixodes ricinus, the vector of Borrelia burgdorferi sensu lato, during the breeding season?

Wild birds are important hosts for vector-borne pathogens, especially those borne by ticks. However, few studies have been conducted on the role of different bird species within a community as hosts of vector-borne pathogens. This study addressed individual and species factors that could explain the burden of Ixodes ricinus on forest birds during the reproductive periods of both vectors and hosts. The goal was to identify which bird species contribute the most to the tick population at the community level. Birds were mist-netted on four plots in 2008 and on seven plots in 2009 in two forests (Sénart and Notre Dame, near Paris, France). The dependence of the tick load per bird upon environmental conditions (questing nymph density, year and plot) and on host species traits (species, age, sex, body size, vertical space use, level of innate and acquired immunity) was analysed. Finally, the relative contribution of each bird species to the local dynamics of ticks was estimated, while accounting for their respective abundance. Tick burden differed markedly between bird species and varied according to questing nymph density. Bird species with a high body mass, those that forage low in the vegetation, and those that had a high innate immune response and a high spleen mass were more likely to have a high tick burden. Four species (the Common Blackbird, Turdus merula, the European Robin, Erithacus rubecula, the Song Thrush, Turdus philomelos, and the Winter Wren, Troglodytes troglodytes) hosted more than 90% of the ticks in the local bird community. These species, and particularly T. merula which was host to a high proportion of the nymphs, are likely to contribute significantly to the circulation of pathogens for which they are competent, such as the agent of Lyme borreliosis.

Prevalence of Buggy Creek virus (Togaviridae: Alphavirus) in insect vectors increases over time in the presence of an invasive avian host

Invasive species can disrupt natural disease dynamics by altering pathogen transmission among native hosts and vectors. The relatively recent occupancy of cliff swallow (Petrochelidon pyrrhonota) nesting colonies in western Nebraska by introduced European house sparrows (Passer domesticus) has led to yearly increases in the prevalence of an endemic arbovirus, Buggy Creek virus (BCRV), in its native swallow bug (Oeciacus vicarius) vector at sites containing both the invasive sparrow host and the native swallow host. At sites without the invasive host, no long-term changes in prevalence have occurred. The percentage of BCRV isolates exhibiting cytopathicity in Vero-cell culture assays increased significantly with year at sites with sparrows but not at swallow-only sites, suggesting that the virus is becoming more virulent to vertebrates in the presence of the invasive host. Increased BCRV prevalence in bug vectors at mixed-species colonies may reflect high virus replication rates in house sparrow hosts, resulting in frequent virus transmission between sparrows and swallow bugs. This case represents a rare empirical example of a pathogen effectively switching to an invasive host, documented in the early phases of the host's arrival in a specialized ecosystem and illustrating how an invasive species can promote long-term changes in host-parasite transmission dynamics.

Introduced Siberian chipmunks (Tamias sibiricus barberi) harbor more-diverse Borrelia burgdorferi sensu lato genospecies than native bank voles (Myodes glareolus)

Little attention has been given in scientific literature to how introduced species may act as a new host for native infectious agents and modify the epidemiology of a disease. In this study, we investigated whether an introduced species, the Siberian chipmunk (Tamias sibiricus barberi), was a potentially new reservoir host for Borrelia burgdorferi sensu lato, the causative agent of Lyme disease. First, we ascertained whether chipmunks were infected by all of the B. burgdorferi sensu lato genospecies associated with rodents and available in their source of infection, questing nymphs. Second, we determined whether the prevalence and diversity of B. burgdorferi sensu lato in chipmunks were similar to those of a native reservoir rodent, the bank vole (Myodes glareolus). Our research took place between 2006 and 2008 in a suburban French forest, where we trapped 335 chipmunks and 671 voles and collected 743 nymphs of ticks that were questing for hosts by dragging on the vegetation. We assayed for B. burgdorferi sensu lato with ear biopsy specimens taken from the rodents and in nymphs using PCR and restriction fragment length polymorphism (RFLP). Chipmunks were infected by the three Borrelia genospecies that were present in questing nymphs and that infect rodents (B. burgdorferi sensu stricto, B. afzelii, and B. garinii). In contrast, voles hosted only B. afzelii. Furthermore, chipmunks were more infected (35%) than voles (16%). These results may be explained by the higher exposure of chipmunks, because they harbor more ticks, or by their higher tolerance of other B. burgdorferi sensu lato genospecies than of B. afzelii. If chipmunks are competent reservoir hosts for B. burgdorferi sensu lato, they may spill back B. burgdorferi sensu lato to native communities and eventually may increase the risk of Lyme disease transmission to humans.