Exploring gaps in our knowledge on Lyme borreliosis spirochaetes--updates on complex heterogeneity, ecology, and pathogenicity

Vector competence of Ixodes ricinus instars for the transmission of Borrelia burgdorferi sensu lato in different small mammalian hosts

BACKGROUND

Many pathogens and parasites can infect multiple host species, and the competence of different hosts as pathogen reservoirs is key to understanding their epidemiology. Small mammals are important hosts for the instar stages of Ixodes ricinus ticks, the principal vector of Lyme disease in Europe. Small mammals also act as reservoirs of Borrelia afzelii, the most common genospecies of the Borrelia burgdorferi sensu lato (s.l.) spirochetes causing Lyme disease in Europe. However, we lack quantitative estimates on whether different small mammal species are equally suitable hosts for feeding I. ricinus and whether they show differences in pathogen transmission from host to tick.

METHODS

Here, we analysed the feeding success and prevalence of B. burgdorferi s.l. infections in 12,987 instar I. ricinus found on captured small mammals with known infection status in Norway (2018-2022).

RESULTS

We found that larvae were more likely to acquire a blood meal from common shrews (Sorex araneus, 46%) compared to bank voles (Myodes glareolus, 36%) and wood mice (Apodemus sylvaticus, 31%). Nymphs tended to be more likely to acquire a blood meal from wood mice (66%) compared to bank voles (54%). Common shrews harboured few nymphs (n=19). Furthermore, we found that larvae feeding on infected bank voles (11%) were more likely to be infected with B. burgdorferi s.l. than larvae on infected common shrews (7%) or wood mice (4%).

CONCLUSIONS

Our study provides quantitative evidence of differences in suitability for the instar stages of I. ricinus across taxa of small mammals and highlights how even known small mammal host species can differ in their ability to feed ticks and infect larval ticks with the pathogen causing Lyme disease.

Individual heterogeneity in ixodid tick infestation and prevalence of Borrelia burgdorferi sensu lato in a northern community of small mammalian hosts

Heterogeneous aggregation of parasites between individual hosts is common and regarded as an important factor in understanding transmission dynamics of vector-borne diseases. Lyme disease is vectored by generalist tick species, yet we have a limited understanding of how individual heterogeneities within small mammal host populations affect the aggregation of ticks and likelihood of infection. Male hosts often have higher parasite and infection levels than females, but whether this is linked to sexual body size dimorphism remains uncertain. Here, we analysed how host species, sex, and body mass influenced Ixodes ricinus tick infestations and the infection prevalence of Borrelia burgdorferi sensu lato (s.l.) in three species of small mammals involved in the enzootic transmission cycle of Lyme disease in Norway from 2018 to 2022. Larval and nymphal ticks were found on 98% and 34% of all individual hosts, respectively. In bank voles and wood mice, both larval and nymphal tick infestation and infection probability increased with body mass, and it increased more with mass for males than for females. Tick infestation in the common shrew increased with body mass and was higher in males, while pathogen infection was higher in females. Sex-biases in infestation did not correspond with level of sexual body mass dimorphism across species. This study contributes to our understanding of how individual heterogeneity among small mammalian hosts influences I. ricinus tick aggregation and prevalence of B. burgdorferi s.l. at northern latitudes.

Molecular detection of Bartonella and Borrelia in pet dogs in Metro Manila and Laguna, Philippines

Background and Aim

Bartonella and Borrelia are zoonotic vector-borne pathogens that can infect dogs and humans. Data on Bartonella and Borrelia in dogs in the Philippines are lacking. This study was conducted to validate previous reports and further investigate the occurrence of Bartonella and Borrelia spp. in cities of Metro Manila.

Materials and Methods

A total of 182 canine blood samples were acquired with DNA using a commercial extraction kit from selected veterinary clinics in the cities of Metro Manila and Laguna, Philippines. The mammalian actin was amplified through polymerase chain reaction (PCR), followed by PCR assays targeting Bartonella gltA and Borrelia flaB. Further PCR assays targeting 16S of Borrelia and ospA and ospC of Borrelia burgdorferi were performed for those that showed flaB bands.

Results

A positive band for gltA of Bartonella was observed in 9 (4.95%) samples, whereas a positive band for flaB of Borrelia was observed in 15 (8.24%) samples. Subsequent PCR assays for other genes of Borrelia were negative.

Conclusion

These results confirmed the presence of Bartonella and warranted further investigation for the possible presence of other Borrelia species.

Transmission Cycle of Tick-Borne Infections and Co-Infections, Animal Models and Diseases

Tick-borne pathogens such as species of Borrelia, Babesia, Anaplasma, Rickettsia, and Ehrlichia are widespread in the United States and Europe among wildlife, in passerines as well as in domestic and farm animals. Transmission of these pathogens occurs by infected ticks during their blood meal, carnivorism, and through animal bites in wildlife, whereas humans can become infected either by an infected tick bite, through blood transfusion and in some cases, congenitally. The reservoir hosts play an important role in maintaining pathogens in nature and facilitate transmission of individual pathogens or of multiple pathogens simultaneously to humans through ticks. Tick-borne co-infections were first reported in the 1980s in white-footed mice, the most prominent reservoir host for causative organisms in the United States, and they are becoming a major concern for public health now. Various animal infection models have been used extensively to better understand pathogenesis of tick-borne pathogens and to reveal the interaction among pathogens co-existing in the same host. In this review, we focus on the prevalence of these pathogens in different reservoir hosts, animal models used to investigate their pathogenesis and host responses they trigger to understand diseases in humans. We also documented the prevalence of these pathogens as correlating with the infected ticks’ surveillance studies. The association of tick-borne co-infections with other topics such as pathogens virulence factors, host immune responses as they relate to diseases severity, identification of vaccine candidates, and disease economic impact are also briefly addressed here.

Redox Imbalance and Its Metabolic Consequences in Tick-Borne Diseases

One of the growing global health problems are vector-borne diseases, including tick-borne diseases. The most common tick-borne diseases include Lyme disease, tick-borne encephalitis, human granulocytic anaplasmosis, and babesiosis. Taking into account the metabolic effects in the patient’s body, tick-borne diseases are a significant problem from an epidemiological and clinical point of view. Inflammation and oxidative stress are key elements in the pathogenesis of infectious diseases, including tick-borne diseases. In consequence, this leads to oxidative modifications of the structure and function of phospholipids and proteins and results in qualitative and quantitative changes at the level of lipid mediators arising in both reactive oxygen species (ROS) and ROS enzyme–dependent reactions. These types of metabolic modifications affect the functioning of the cells and the host organism. Therefore, links between the severity of the disease state and redox imbalance and the level of phospholipid metabolites are being searched, hoping to find unambiguous diagnostic biomarkers. Assessment of molecular effects of oxidative stress may also enable the monitoring of the disease process and treatment efficacy.

Transmission patterns of tick-borne pathogens among birds and rodents in a forested park in southeastern Canada

Ixodes scapularis ticks are expanding their range in parts of northeastern North America, bringing with them pathogens of public health concern. While rodents like the white-footed mouse, Peromyscus leucopus, are considered the primary reservoir of many emerging tick-borne pathogens, the contribution of birds, as alternative hosts and reservoirs, to local transmission cycles has not yet been firmly established. From 2016 to 2018, we collected host-seeking ticks and examined rodent and bird hosts for ticks at 48 sites in a park where blacklegged ticks are established in Quebec, Canada, in order to characterize the distribution of pathogens in ticks and mammalian and avian hosts. We found nearly one third of captured birds (n = 849) and 70% of small mammals (n = 694) were infested with I. scapularis. Five bird and three mammal species transmitted Borrelia burgdorferi to feeding larvae (n larvae tested = 2257) and we estimated that about one fifth of the B. burgdorferi-infected questing nymphs in the park acquired their infection from birds, the remaining being attributable to mice. Ground-foraging bird species were more parasitized than other birds, and species that inhabited open habitat were more frequently infested and were more likely to transmit B. burgdorferi to larval ticks feeding upon them. Female birds were more likely to transmit infection than males, without age differentiation, whereas in mice, adult males were more likely to transmit infection than juveniles and females. We also detected Borrelia miyamotoi in larvae collected from birds, and Anaplasma phagocytophilum from a larva collected from a white-footed mouse. This study highlights the importance of characterising the reservoir potential of alternative reservoir hosts and to quantify their contribution to transmission dynamics in different species assemblages. This information is key to identifying the most effective host-targeted risk mitigation actions.

Evidence of Borrelia theileri in Wild and Domestic Animals in the Kafue Ecosystem of Zambia

Members of the genus Borrelia are arthropod-borne spirochetes that are human and animal pathogens. Vertebrate hosts, including wild animals, are pivotal to the circulation and maintenance of Borrelia spirochetes. However, information on Borrelia spirochetes in vertebrate hosts in Zambia is limited. Thus, we aimed to investigate the presence of Borrelia spirochetes in wild animals and cattle in Zambia. A total of 140 wild animals of four species and 488 cattle DNA samples from /near the Kafue National Park were collected for real-time PCR screening, followed by characterization using three different genes with positive samples. Five impalas and 20 cattle tested positive using real-time PCR, and sequence analysis revealed that the detected Borrelia were identified to be Borrelia theileri, a causative agent of bovine borreliosis. This is the first evidence of Borrelia theileri in African wildlife and cattle in Zambia. Our results suggest that clinical differentiation between bovine borreliosis and other bovine diseases endemic in Zambia is required for better treatment and control measures. As this study only included wild and domestic animals in the Kafue ecosystem, further investigations in other areas and with more wildlife and livestock species are needed to clarify a comprehensive epidemiological status of Borrelia theileri in Zambia.

Tick-borne zoonotic agents infecting horses from an urban area in Midwestern Brazil: epidemiological and hematological features

The emergence of tick-borne diseases has been reported as a serious problem in public health worldwide and many aspects of its epidemiology and effects on the health of its hosts are unclear. We aimed to perform an epidemiological study of tick-borne zoonotic Rickettsia, Borrelia, and Anaplasmataceae in horses from Midwestern Brazil. We also evaluated whether Borrelia spp. and Anaplasmataceae may be associated with hematological disorders in the sampled animals. Blood and serum samples as well as ticks were collected from 262 horses. Serum samples were used to perform serological tests, and hematological analyses were made using whole blood. Furthermore, DNA extracted from whole blood and ticks was used for molecular tests. Campo Grande is enzootic for tick-borne studied bacteria, since we found an overall exposure of 59.9% of the sampled horses, 28.7% of them presented co-exposure. Seropositivity rates of 20.6% for Borrelia spp., 25.6% for Rickettsia spp., and 31.6% for Anaplasmataceae were found in the sampled horses. Considering both molecular and serological tests for Borrelia spp., the infection rate was 48.0% (126/262). None of the tested horses showed molecular positivity for Anaplasma phagocytophilum. The horses sampled displayed 7.2% of parasitism by ixodid ticks in single and coinfestations. We did not find DNA of any studied bacteria in the sampled ticks. Positive horses for Borrelia spp. and Anaplasmataceae agents displayed leukopenia, monocytopenia, and lymphopenia. Together, our results suggest that horses may play a role as sentinel host for zoonotic bacteria and Borrelia spp. and Anaplasmataceae agents can impair the health of horses.

Unexpected failure of Ixodes scapularis nymphs to transmit a North American Borrelia bissettiae strain

Globally, the Borrelia burgdorferi (sensu lato) complex comprises more than 21 species of spirochetes. Although the USA is home to a diverse fauna of Lyme disease group Borrelia species, only two are considered responsible for human clinical disease: Borrelia burgdorferi (sensu stricto) and Borrelia mayonii. However, evidence has implicated additional B. burgdorferi (s.l.) species in human illness elsewhere. While much research has focused on the B. burgdorferi (s.s.)-tick interface, tick vectors for most of the other North American Lyme disease group Borrelia species remain experimentally unconfirmed. In this report we document the ability of Ixodes scapularis to acquire but not transmit a single strain of Borrelia bissettiae, a potential human pathogen, in a murine infection model. Pathogen-free I. scapularis larvae were allowed to feed on mice with disseminated B. burgdorferi (s.s.) or B. bissettiae infections. Molted infected nymphs were then allowed to feed on naïve mice to assess transmission to a susceptible host through spirochete culture and qPCR throughout in ticks collected at various developmental stages (fed larvae and nymphs, molted nymphs, and adults). In this study, similar proportions of I. scapularis larvae acquired B. bissettiae and B. burgdorferi (s.s.) but transstadial passage to the nymphal stage was less effective for B. bissettiae. Furthermore, B. bissettiae-infected nymphs did not transmit B. bissettiae infection to naïve susceptible mice as determined by tissue culture and serology. In the tick, B. bissettiae spirochete levels slightly increased from fed larvae to molted and then fed nymphs, yet the bacteria were absent in molted adults. Moreover, in contrast to B. burgdorferi (s.s.), B. bissettiae failed to exponentially increase in upon completion of feeding in our transmission experiment. In this specific model, I. scapularis was unable to support B. bissettiae throughout its life-cycle, and while live spirochetes were detected in B. bissettiae-infected ticks fed on naïve mice, there was no evidence of murine infection. These data question the vector competence of Ixodes scapularis for B. bissettiae. More importantly, this specific B. bissettiae-I. scapularis model may provide a tool for researchers to delineate details on mechanisms involved in Borrelia-tick compatibility.

Vertigo as One of the Symptoms of Lyme Disease

Objectives: The aim of the study was to evaluate the frequency of vertigo symptoms and potential labyrinth damage in patients with diagnosed Lyme disease (LD). LD can affect the vestibulocochlear nerve, leading to hearing loss and vertigo/dizziness. Material and Methods: The study included a group of 38 patients between the ages of 20 and 77, who were hospitalized due to vertigo/dizziness between 2018 and 2019. All of the patients underwent a detailed medical interview and an otolaryngological and neurological examination, including video electronystagmography (VENG), in addition to audiological and diagnostic tests. Additionally, ELISA and Western blot tests were performed to confirm the diagnosis of LD. Results: In 20 patients (53%), the Romberg trial was positive (p < 0.001). The degree of vestibular dysfunction as shown by the VENG test was associated with the rate of hearing loss as confirmed by the Auditory Brainstem Response (ABR) test (p = 0.011), and it mainly concerned high-frequency sounds (p = 0.014). Conclusion: Vertigo can be a symptom of LD. It is often associated with labyrinth and hearing-organ damage, which can imply that the inner ear or nerve VIII is dysfunctional in the course of this disease. Antibiotic therapy is effective in reducing otoneurological symptoms.

The evolution of hard tick-borne relapsing fever borreliae is correlated with vector species rather than geographical distance

Background

Relapsing fever (RF) borreliae are arthropod-borne spirochetes and some of them cause human diseases, which are characterized by relapsing or recurring episodes of fever. Recently, it has been classified into two groups: soft tick-borne RF (STRF) borreliae and hard tick-borne RF (HTRF) borreliae. STRF borreliae include classical RF agents and HTRF borreliae, the latter of which include B. miyamotoi, a human pathogen recently identified in Eurasia and North America.

Results

In this study, we determined the genome sequences of 16 HTRF borreliae strains: 15 B. miyamotoi strains (9 from Hokkaido Island, Japan, 3 from Honshu Island, Japan, and 3 from Mongolia) and a Borrelia sp. tHM16w. Chromosomal gene synteny was highly conserved among the HTRF strains sequenced in this study, even though they were isolated from different geographic regions and different tick species. Phylogenetic analysis based on core gene sequences revealed that HTRF and STRF borreliae are clearly distinguishable, with each forming a monophyletic group in the RF borreliae lineage. Moreover, the evolutionary relationships of RF borreliae are consistent with the biological and ecological features of each RF borreliae sublineage and can explain the unique characteristics of Borrelia anserina. In addition, the pairwise genetic distances between HTRF borreliae strains were well correlated with those of vector species rather than with the geographical distances between strain isolation sites. This result suggests that the genetic diversification of HTRF borreliae is attributed to the speciation of vector ticks and that this relationship might be required for efficient transmission of HTRF borreliae within vector ticks.

Conclusions

The results of the present study, together with those from previous investigations, support the hypothesis that the common ancestor of borreliae was transmitted by hard-bodied ticks and that only STRF borreliae switched to using soft-bodied ticks as a vector, which was followed by the emergence of Borrelia recurrentis, lice-borne RF borreliae. Our study clarifies the phylogenetic relationships between RF borreliae, and the data obtained will contribute to a better understanding of the evolutionary history of RF borreliae.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01838-1.

Monitoring of pathogenic Borrelia burgdorferi sensu lato in the Almaty oblast, Kazakhstan

Lyme borreliosis (LB) is one of the most common vector-borne diseases transmitted by ticks. It is caused by the Borrelia burgdorferi sensu lato (s.l.) genospecies. The Almaty oblast of Kazakhstan is considered endemic for LB. Nevertheless, there are significant gaps in the tick surveillance for LB agents in the region. We evaluated B. burgdorferi s.l. prevalence in 413 ixodid ticks collected from bitten people and the seroprevalence of antibodies to B. burgdorferi s.l. in 589 residents of the Almaty oblast, Kazakhstan. All samples were collected between 2018 and 2020. Borrelia burgdorferi s.l. DNA was detected in 24 % (9/38) of I. persulcatus ticks that attacked humans in the city of Almaty and the Talgar and Karasay districts. Multilocus sequence typing identified two novel B. afzelii sequence types in I. persulcatus. The seroprevalence of IgG antibodies against B. burgdorferi s.l. in the analyzed population was detected to be 5.8 %. The obtained results confirm active circulation of B. burgdorferi s.l. in the Almaty oblast of Kazakhstan and raise concern regarding LB preventive measures in the region.

The prevalence of Borrelia in Ixodes persulcatus in southeastern Kazakhstan

Borreliosis is one of the most common vector-borne zoonotic diseases in the world. Limited data are available regarding Borrelia spp. and their genotypes in Kazakhstan. The goal of this study was to investigate the prevalence of Borrelia spp. in ixodid ticks collected in the southeastern region of Kazakhstan. A total of 1907 ixodid ticks were collected by flagging vegetation at three collection areas in the Almaty oblast between 2015 and 2018. They were grouped into 407 pools and examined by qPCR for Borrelia burgdorferi sensu lato (s.l.). A conventional PCR with specific primers targeting 16S rRNA gene was used to differentiate B. burgdorferi s.l. genospecies. Sequence analysis of the PCR products was performed for sixteen samples. Lyme borreliosis agents were only detected in adult questing Ixodes persulcatus. The overall B. burgdorferi s.l. prevalence in I. persulcatus estimated as the minimum infection rate reached 10.7 %. Borrelia burgdorferi sensu stricto was not detected in any of the tick pools. Partial 16S rRNA gene sequencing revealed the presence of B. miyamotoi, B. afzelii, and B. garinii. Borrelia afzelii was the dominant genospecies in Almaty oblast. A significantly lower proportion of B. garinii positive tick pools was detected in the Zailiyskiy Alatau as compared to the Dzungarian Alatau (χ² = 16.243; p = 0.0001) and Yenbekshikazakh district (χ² = 7.4156; p = 0.0065). The obtained results indicate the epidemiological significance of B. afzelii and B. garinii in southeastern Kazakhstan. These new data aim to improve the diagnostics of Lyme borreliosis and monitoring of tick-borne infections in Kazakhstan.

Strong interactions between Salp15 homologues from the tick I. ricinus and distinct types of the outer surface OspC protein from Borrelia

Ticks belonging to the genus Ixodes are parasites feeding on vertebrate blood and vectors for many pathogenic microbes, including Borrelia burgdorferi sensu lato spirochetes, the causative agent of Lyme borreliosis. The tick saliva contains a mixture of bioactive molecules showing a wide range of properties for efficient engorgement. One of the most extensively studied components of tick saliva is a 15-kDa salivary gland protein (Salp15) from Ixodes scapularis. This multifunctional protein suppresses the immune response of hosts through pleiotropic action on a few crucial defense pathways. Salp15 and its homologue from I. ricinus Iric1 have been also shown to bind to Borrelia burgdorferi sensu stricto outer surface protein C (OspC) permitting the spirochetes to evade antibody-mediated killing in the human host. Further studies revealed that Salp15 and Iric1 protected B. burgdorferi s. s. and B. garinii expressing OspC against the complement system. OspC is the most variable protein on the outer surface of Borrelia, which in addition to Salp15 can also bind other ligands, such as plasminogen, fibrinogen, fibronectin or complement factor 4. So far several OspC variants produced by B. burgdorferi s. l. spirochetes were shown to be capable of binding Salp15 or its homologue, but the protection against borreliacidal antibodies has only been proven in the case of B. burgdorferi s. s. The question of Salp15 contribution to Borrelia survival during the infection has been comprehensively studied during the last decades. In contrast, the organization of the OspC-Salp15 complex has been poorly explored. This report describes the binding between three Salp15 homologues from the tick Ixodes ricinus (Iric1, Iric2 and Iric3) and OspC from four B. burgdorferi sensu lato strains in terms of the binding parameters, analyzed with two independent biophysical methods - Microscale thermophoresis (MST) and Biolayer interferometry (BLI). The results of both experiments show a binding constant at the nanomolar level, which indicates very strong interactions. While the Iric1-OspC binding has been reported before, we show in this study that also Iric2 and Iric3 are capable of OspC binding with high affinity. This observation suggests that these two Salp15 homologues might be used by B. burgdorferi s. l. in a way analogous to Iric1. A comparison of the results from the two methods let us propose that N-terminal immobilization of OspC significantly increases the affinity between the two proteins. Finally, our results indicate that the Iric binding site is located in close proximity of the OspC epitopes recognized by human antibodies, which may have important biological and medical implications.

Migratory birds as disseminators of ticks and the tick-borne pathogens Borrelia bacteria and tick-borne encephalitis (TBE) virus: a seasonal study at Ottenby Bird Observatory in South-eastern Sweden

Background

Birds can act as reservoirs of tick-borne pathogens and can also disperse pathogen-containing ticks to both nearby and remote localities. The aims of this study were to estimate tick infestation patterns on migratory birds and the prevalence of different Borrelia species and tick-borne encephalitis virus (TBEV) in ticks removed from birds in south-eastern Sweden.

Methods

Ticks were collected from resident and migratory birds captured at the Ottenby Bird Observatory, Öland, Sweden, from March to November 2009. Ticks were molecularly identified to species, and morphologically to developmental stage, and the presence of Borrelia bacteria and TBEV was determined by quantitative real-time PCR.

Results

A total of 1339 ticks in the genera Haemaphysalis, Hyalomma, and Ixodes was recorded of which I. ricinus was the most abundant species. Important tick hosts were the European robin (Erithacus rubecula), Blackbird (Turdus merula), Tree pipit (Anthus trivialis), Eurasian wren (Troglodytes troglodytes), Common redstart (Phoenicurus phoenicurus), Willow warbler (Phylloscopus trochilus), and Common whitethroat (Sylvia communis). Borrelia bacteria were detected in 25% (285/1,124) of the detached ticks available for analysis. Seven Borrelia species (B. afzelii, B. burgdorferi (s.s.), B. garinii, B. lusitaniae, B. turdi, B. valaisiana, and B. miyamotoi) were identified. B. turdi was recorded for the first time in ticks in Sweden. The number of Borrelia cells per tick ranged from 2.0 × 10⁰ to 7.0 × 10⁵. B. miyamotoi-containing ticks contained a significantly higher median number of Borrelia cells than B. burgdorferi (s.l.)-containing ticks. B. garinii and B. miyamotoi were the most prevalent Borrelia species in tick larvae. Larvae of I. ricinus with B. garinii were removed from seven bird species, particularly S. communis and A. trivialis, which may suggest that the larvae had contracted the Borrelia bacteria from or via these birds. Also, a high percentage of tick larvae containing B. miyamotoi was removed from E. rubecula. All ticks were negative for TBEV.

Conclusions

The results corroborate the view that the contributions of birds to human disease are substantial, particularly as blood hosts for ticks and for their short-, medium-, and long-distance dispersal. Moreover, several ground-foraging bird species appear to be important for the maintenance and dispersal of Borrelia species. The absence of TBEV in the ticks conforms to other similar studies.

The Unexpected Holiday Souvenir: The Public Health Risk to UK Travellers from Ticks Acquired Overseas

Overseas travel to regions where ticks are found can increase travellers' exposure to ticks and pathogens that may be unfamiliar to medical professionals in their home countries. Previous studies have detailed non-native tick species removed from recently returned travellers, occasionally leading to travel-associated human cases of exotic tick-borne disease. There are 20 species of tick endemic to the UK, yet UK travellers can be exposed to many other non-native species whilst overseas. Here, we report ticks received by Public Health England's Tick Surveillance Scheme from humans with recent travel history between January 2006 and December 2018. Altogether, 16 tick species were received from people who had recently travelled overseas. Confirmed imports (acquired outside of the UK) were received from people who recently travelled to 22 countries. Possible imports (acquired abroad or within the UK) were received from people who had recently travelled to eight European countries. Species-specific literature reviews highlighted nine of the sixteen tick species are known to vector at least one tick-borne pathogen to humans in the country of acquisition, suggesting travellers exposed to ticks may be at risk of being bitten by a species that is a known vector, with implications for novel tick-borne disease transmission to travellers.

Livestock owners' worry and fear of tick-borne diseases

Background

Recent global changes have led to an increase in distribution of ticks towards higher elevation and latitude in Europe and livestock are at increasing risk of contracting tick-borne diseases, but psychological aspects of how this affects human well-being are rarely assessed. Departing from the theory on emotional appraisal coming from psychology, this study investigates which factors that modulate worry and fear associated with the presence of ticks among livestock owners of sheep and/or cattle.

Methods

Survey data from 775 livestock owners in Norway were analysed by hierarchical multiple regression analysis with an index of fear of tick-borne diseases among livestock as the outcome variable.

Results

Twenty-nine per cent of the livestock owners reported worry and fear of tick-borne diseases among their livestock. The model explained 35% of the variance in worry and fear. There was a weak association between estimated incidences of tick-borne diseases in livestock and livestock owners’ worry and fear. Whereas previous personal experience of ticks and tick-borne diseases in livestock, and the livestock owners’ appraisals of the situation were more strongly associated with relatively stronger feelings of worry and fear.

Conclusions

Livestock owners’ worry and fear of tick-borne diseases in livestock can partly be understood as their appraisals of perceived personal relevance of the presence of ticks, its potential negative implications for their daily life at large, and what potential they have to cope by different strategies to adapt or adjust to the situation.

Polymorphism of TLR2 in bank vole populations in North Eastern Poland is not associated with Borrelia afzelii infection prevalence

Polymorphism in innate immune genes in host populations can structure spatial variation in the prevalence of infectious diseases. In Europe, Borrelia afzelii is an important tick-borne pathogen of small mammals including the bank voles (Myodes glareolus). The Toll-like receptor 2 (TLR2) is an innate immune receptor that is important for detecting Borrelia burgdorferi sensu lato pathogens. The TLR2 gene is polymorphic in bank vole populations and is classified into four distinct clusters: C1, C2, C3, and C4. The C2 and C4 clusters versus the C1 and C3 clusters are associated with lower versus higher infection prevalence, respectively. We detected three TLR2 clusters in 487 bank voles from 30 populations in NE Poland: 84.2% of the obtained sequences belonged to the C1 variant, 7.2% to C2, and 8.6% to C3. However, no clear spatial structure of TLR2 clusters among the populations was detected. B. afzelii infection prevalence across all studied individuals was 12.1% and varied from 0 to 37.5% among populations. There were no significant differences in B. afzelii prevalence among voles carrying alleles of different TLR2 clusters, or between individuals belonging to two mtDNA lineages. Most infected individuals were adults, and males were infected more often than females. There was no significant relationship between the prevalence of TLR2 clusters in the vole populations and climatic and environmental factors within the study area. We therefore could not confirm an adaptive role of the TLR2 C2 alleles in reducing B. afzelii infection prevalence in bank voles.

Molecular detection of Rickettsia spp., Borrelia spp., Bartonella spp. and Yersinia pestis in ectoparasites of endemic and domestic animals in southwest Madagascar

Little is known about the presence of vector-borne bacteria in southwest Madagascar. Anthropogenic alteration of natural habitats represents an important driver for the emergence of new diseases. Especially the involvement of livestock and the involuntary maintaining of invasive synanthropic animals (particularly rats) facilitate disease transmission from wildlife to humans and associated animals and vice versa. The dissemination or acquisition of ectoparasites is most likely in regions where human/wildlife contact is increasing. Little is known about the presence of vector-borne bacteria in southwest Madagascar. In 2016 and 2017, ectoparasites were collected from various introduced (cattle and goats, cats, dogs and chicken, rats and mice) and native animal species (mouse lemurs [Microcebus griseorufus], Grandidier's mongooses [Galidictis grandidieri], bastard big-footed mice [Macrotarsomys bastardi], greater hedgehog tenrecs [Setifer setosus] and lesser hedgehog tenrecs [Echinops telfairi]) in the northern portion of Tsimanampetsotsa National Park and the adjacent littoral region. Thirteen species of blood-feeding ectoparasites (235 individuals of ticks [5 species], 414 lice [4 spp.] and 389 fleas [4 spp.]) were investigated for the presence and identity of rickettsiae, borreliae, bartonellae and Yersinia pestis using PCR techniques. Rickettsia spp. were detected in every single ectoparasite species (Amblyomma variegatum, A. chabaudi, Rhipicephalus microplus, Haemaphysalis simplex, Argas echinops, Ctenocephalides felis, Echidnophaga gallinacea, Pulex irritans, Xenopsylla cheopis, Haematopinus quadripertusus, Linognathus africanus, L. vituli, Lemurpediculus verruculosus). Lice and ticks were found harboring rickettsiae identified as Rickettsia africae, while Rickettsia felis-like bacteria were associated with fleas. Borrelia spp. were detected in 5% of H. simplex and 1% of R. microplus ticks. Bartonella spp. were detected in 40% of H. quadripertusus pools and in 5% of L. verruculosus pools. Y. pestis was detected in X. cheopis and E. gallinacea fleas collected from a rat. This study presents the detection of a broad spectrum of vector-borne bacteria including potential pathogens, and an unexpected finding of Y. pestis far off the known plague foci in Madagascar.

Broadly Protective Multivalent OspA Vaccine against Lyme Borreliosis, Developed Based on Surface Shaping of the C-Terminal Fragment

The development of vaccines for prevention of diseases caused by pathogenic species can encounter major obstacles if high sequence diversity is observed between individual strains. Therefore, development might be restricted either to conserved antigens, which are often rare, or to multivalent vaccines, which renders the production more costly and cumbersome. In light of this complexity, we applied a structure-based surface shaping approach for the development of a Lyme borreliosis (LB) vaccine suitable for the United States and Europe. The surface of the C-terminal fragment of outer surface protein A (OspA) was divided into distinct regions, based primarily on binding sites of monoclonal antibodies (MAbs). In order to target the six clinically most relevant OspA serotypes (ST) in a single protein, exposed amino acids of the individual regions were exchanged to corresponding amino acids of a chosen OspA serotype. Six chimeric proteins were constructed, and, based on their immunogenicity, four of these chimeras were tested in mouse challenge models. Significant protection could be demonstrated for all four proteins following challenge with infected ticks (OspA ST1, OspA ST2, and OspA ST4) or with in vitro-grown spirochetes (OspA ST1 and OspA ST5). Two of the chimeric proteins were linked to form a fusion protein, which provided significant protection against in vitro-grown spirochetes (OspA ST1) and infected ticks (OspA ST2). This article presents the proof-of-concept study for a multivalent OspA vaccine targeting a wide range of pathogenic LB Borrelia species with a single recombinant antigen for prevention of Lyme borreliosis.

Lyme Disease Frontiers: Reconciling Borrelia Biology and Clinical Conundrums

Lyme disease is a complex tick-borne zoonosis that poses an escalating public health threat in several parts of the world, despite sophisticated healthcare infrastructure and decades of effort to address the problem. Concepts like the true burden of the illness, from incidence rates to longstanding consequences of infection, and optimal case management, also remain shrouded in controversy. At the heart of this multidisciplinary issue are the causative spirochetal pathogens belonging to the Borrelia Lyme complex. Their unusual physiology and versatile lifestyle have challenged microbiologists, and may also hold the key to unlocking mysteries of the disease. The goal of this review is therefore to integrate established and emerging concepts of Borrelia biology and pathogenesis, and position them in the broader context of biomedical research and clinical practice. We begin by considering the conventions around diagnosing and characterizing Lyme disease that have served as a conceptual framework for the discipline. We then explore virulence from the perspective of both host (genetic and environmental predispositions) and pathogen (serotypes, dissemination, and immune modulation), as well as considering antimicrobial strategies (lab methodology, resistance, persistence, and clinical application), and borrelial adaptations of hypothesized medical significance (phenotypic plasticity or pleomorphy).

Diversity of Lyme borreliosis spirochetes isolated from ticks in Serbia

Spirochetes from the Borrelia burgdorferi sensu lato (s.l.). (Spirochaetales: Spirochaetaceae) species complex, including the causative agents of Lyme borreliosis, have been isolated from ticks, vertebrate reservoirs and humans. Previous analyses based on direct molecular detection in ticks indicated a considerable diversity of B. burgdorferi s.l. complex in Serbia. The present study aimed (a) to isolate borrelia strains from Serbia; (b) to determine their genotypic characteristics; and (c) to establish a collection of viable B. burgdorferi s.l. strains for further biological, ecological and genetic studies. For the present study, 231 adult Ixodes ricinus (Ixodida: Ixodidae) ticks from 16 ecologically different localities in Serbia were individually processed to cultivate B. burgdorferi s.l. This led to the isolation of 36 strains. A hbb gene quantitative real-time polymerase chain reaction (PCR) based on melting temperature determination and ospA gene sequencing were used to genotype the isolated spirochetes. The species identified based on the hbb gene real-time PCR were: Borrelia lusitaniae (44.4%), Borrelia afzelii (36.1%), Borrelia garinii (13.9%) and Borrelia valaisiana (5.6%), whereas the ospA sequence analysis revealed the occurrence of Borrelia bavariensis. This is the first report of the isolation of B. lusitaniae, B. garinii, B. bavariensis and B. valaisiana strains in Serbia.

First records of tick-borne pathogens in populations of the taiga tick Ixodes persulcatus in Sweden

Background

The common tick Ixodes ricinus and the taiga tick I. persulcatus are the main tick vectors of Borrelia spirochaetes, TBE virus (TBEV) and of several other zoonotic pathogens in the western and eastern areas, respectively of the Palaearctic region. Recently, populations of the taiga tick were, for the first time, detected in northern Sweden. This prompted us to investigate if they harbour human pathogens.

Methods

A total of 276 I. persulcatus ticks (136 males, 126 females and 14 nymphs) and one I. ricinus nymph was collected by the cloth-dragging method in northern Sweden in July–August 2015 and May–July 2016. In addition, 8 males and 10 females of I. persulcatus were collected from two dogs (16 and 2 ticks, respectively) in two of the localities. All ticks were microscopically and molecularly identified to developmental stage and species and screened for B. burgdorferi (sensu lato), B. miyamotoi, Anaplasma phagocytophilum, Rickettsia spp., Neoehrlichia mikurensis, Babesia spp. and TBEV using real-time PCR followed by species identification by sequencing the PCR-products of conventional PCR assays.

Results

Of the ticks collected by the cloth-dragging method, 55% (152/277) were positive for Borrelia. There was no significant difference between the proportions of Borrelia-infected nymphs (33%, 5/15) and Borrelia-infected adult ticks (56%, 147/262), and no significant difference between the proportions of Borrelia-infected males (54%, 74/136) and Borrelia-infected females (58%, 73/126). Three different Borrelia species were identified. Borrelia afzelii was the predominant species and detected in 46% of all Borrelia-infected ticks followed by B. garinii, 35%, B. valaisiana, 1%, and mixed infections of different Borrelia species, 1%; 17% of all Borrelia-infections were untypeable. One I. persulcatus female contained Rickettsia helvetica, and one nymph contained Rickettsia sp. Of the 277 ticks analysed, all were negative for A. phagocytophilum, Babesia spp., Borrelia miyamotoi, N. mikurensis and TBEV. The ticks collected from the two dogs were negative for all pathogens examined except for Borrelia spp., that was detected in 5 out of 16 ticks removed from one of the dogs.

Conclusions

To our knowledge, this is the first time that I. persulcatus from Sweden has been analysed for the presence of tick-borne pathogens. The examined tick populations had a low diversity of tick-borne pathogens but a high prevalence of B. burgdorferi (s.l.).

Prevalence of pathogens in ticks collected from humans through citizen science in Belgium

BACKGROUND

In order to evaluate the risk of human exposure to tick-borne pathogens in Belgium, a study on the prevalence of several pathogens was conducted on feeding ticks removed from humans in 2017.

METHODS

Using a citizen science approach based on an existing notification tool for tick bites, a sample of ticks was collected across the country. Collected ticks were screened by PCR for the presence of the following pathogens: Anaplasma phagocytophilum, Babesia spp., Borrelia burgdorferi (sensu lato), Borrelia miyamotoi, Neoehrlichia mikurensis, Rickettsia helvetica and tick-borne encephalitis virus (TBEV).

RESULTS

In total, 1599 ticks were included in the sample. The great majority of ticks belonged to Ixodes ricinus (99%); other tick species were identified as Ixodes hexagonus (0.7%) and Dermacentor reticulatus (0.3%). Borrelia burgdorferi (s.l.) was detected in 14% of nymphs and adult ticks. Adult ticks (20%) were more likely to be infected than nymphs (12%). The most common genospecies were B. afzelii (52%) and B. garinii (21%). Except for TBEV, the other tick-borne pathogens studied were all detected in the tick sample, although at a lower prevalence: 1.5% for Babesia spp.; 1.8% for A. phagocytophilum; 2.4% for B. miyamotoi; 2.8% for N. mikurensis; and 6.8% for R. helvetica. Rickettsia raoultii, the causative agent of tick-borne lymphadenopathy, was identified for the first time in Belgium, in two out of five D. reticulatus ticks. Co-infections were found in 3.9% of the examined ticks. The most common co-infection was B. burgdorferi (s.l.) + N. mikurensis.

CONCLUSIONS

Although for most of the tick-borne diseases in Belgium, other than Lyme borreliosis, no or few cases of human infection are reported, the pathogens causing these diseases were all (except for TBEV) detected in the tick study sample. Their confirmed presence can help raise awareness among citizens and health professionals in Belgium on possible diseases other than Lyme borreliosis in patients presenting fever or other non-characteristic symptoms after a tick bite.

Candidatus Neoehrlichia sp. (FU98) and Borrelia burgdorferi Sensu Lato in Red Foxes (Vulpes vulpes) from Serbia

Human activities such as deforestation, urbanization, and environmental pollution lead to a reduction in the spatial boundary between wild animals, domestic animals and humans. These activities increase the risk for the emergence of pathogens from the sylvatic cycle in the population of domestic animals and humans. Foxes are recognized as potential reservoirs for a number of bacterial pathogens of medical and public health concern. The aim of the present study was to investigate the prevalence and spatial distribution of bacterial tick-borne pathogens from the Anaplasmataceae family, Borrelia burgdorferi sensu lato (s.l.), Rickettsia spp., Coxiella burnetii, Francisella tularensis, Bartonella spp., in the red fox population from Serbia and to discuss the obtained results from the epidemiological point of view. Legally hunted red foxes (Vulpes vulpes) from 14 localities in Serbia were included in the study and spleen samples from 129 animals were tested with conventional PCR assays for the presence of bacterial tick-borne pathogens. DNA of Candidatus Neoehrlichia sp. (FU98), Borrelia burgdorferi sensu stricto, Borrelia lusitaniae, and Borrelia garinii was detected in 6 (4.7%), 1 (0.8%), 2 (1.6%) and 1 (0.8%) animals, respectively. Co-infection by Candidatus Neoehrlichia sp. (FU98) and B. garinii was detected in one animal. All samples were negative for other tested bacterial tick-borne pathogens. The results of the present study indicate the potential role of foxes in natural cycles of Candidatus Neoehrlichia sp. (FU98) and causative agents of Lyme borreliosis in the investigated areas. Further research is required to elucidate the role of foxes in the epidemiology of these and other tick-borne zoonotic pathogens in the Republic of Serbia.

Prevalence of Anaplasma phagocytophilum in humans in Belgium for the period 2013-2016

Ticks are vectors for a broad range of pathogens of medical and veterinary importance, such as Borrelia spp., Babesia spp., Anaplasma spp., Rickettsia spp., Bartonella spp. and the tick-borne encephalitis virus. The Gram-negative bacterium Anaplasma phagocytophilum is present worldwide, including Belgium where numerous patients were shown to harbour antibodies against this pathogen as recorded by the Belgian National Reference Center (NRC) for Anaplasma. The clinical presentation of human granulocytic anaplasmosis is an acute, febrile, nonspecific, flu-like illness. Leukopenia, thrombocytopenia and increased hepatic transaminase activities are commonly present early in the disease. Diagnosis early in the course of infection relies on the detection of antibodies or of the bacterium in the blood, as is performed at the NRC for Anaplasma, part of the Clinical Laboratory of the Queen Astrid Military Hospital in Brussels, Belgium. In this article, we discuss diagnostic test results as well as recent clinical and demographic characteristics of patients whose samples were analyzed by the NRC for Anaplasma in a four-year period (2013-2016).

Lyme neuroborreliosis and bird populations in northern Europe

Many vector-borne diseases are transmitted through complex pathogen-vector-host networks, which makes it challenging to identify the role of specific host groups in disease emergence. Lyme borreliosis in humans is now the most common vector-borne zoonosis in the Northern Hemisphere. The disease is caused by multiple genospecies of Borrelia burgdorferi sensu lato bacteria transmitted by ixodid (hard) ticks, and the major host groups transmit Borrelia genospecies with different pathogenicity, causing variable clinical symptoms in humans. The health impact of a given host group is a function of the number of ticks it infects as well as the pathogenicity of the genospecies it carries. Borrelia afzelii, with mainly small mammals as reservoirs, is the most common pathogen causing Lyme borreliosis, and it is often responsible for the largest proportion of infected host-seeking tick nymphs in Europe. The bird-borne Borrelia garinii, though less prevalent in nymphal ticks, is more likely to cause Lyme neuroborreliosis, but whether B. garinii causes disseminated disease more frequently has not been documented. Based on extensive data of annual disease incidence across Norway from 1995 to 2017, we show here that 69% of disseminated Lyme borreliosis cases were neuroborreliosis, which is three times higher than predicted from the infection prevalence of B. garinii in host-seeking ticks (21%). The population estimate of migratory birds, mainly of thrushes, explained part of the annual variation in cases of neuroborreliosis, with a one-year time lag. We highlight the important role of the genospecies' pathogenicity and the host associations for understanding the epidemiology of disseminated Lyme borreliosis.

How general are generalist parasites? The small mammal part of the Lyme disease transmission cycle in two ecosystems in northern Europe

The pathogens causing Lyme disease are all vectored by generalist tick species found on a wide range of vertebrates, but spatial and annual variation in host use has rarely been quantified. We here compare the load of Ixodes ricinus (the vector) on small mammals and investigate the infection prevalence of Borrelia burgdorferi s.l. (the pathogen) involved in the enzootic transmission cycle of Lyme disease in two contrasting ecosystems in Norway from 2014 to 2016. The most common larval tick host in the eastern region was the bank vole, while the common shrew dominated in the western region of Norway. However, the wood mouse and the bank vole had consistently higher larval tick loads than the common shrew in both ecosystems. Hence, the evidence indicated that species are differently suitable as hosts, regardless of their abundances. The pathogen infection prevalence was similar among small mammal species, but markedly higher in the region with larger small mammal populations and higher tick loads, while the seasonal and annual variation was less marked. Our study indicated that the generalist I. ricinus shows consistent patterns of load on species of small vertebrate hosts, while B. burgdorferi s.l. (B. afzelii) was a true generalist. The similar roles of host species across regions suggest that disease dynamics can be predicted from host community composition, but predicting the role of host community composition for disease dynamics requires a detailed understanding of the different species population limitations under global change.

Genospecies of Borrelia burgdorferi sensu lato detected in 16 mammal species and questing ticks from northern Europe

Lyme borreliosis is the most common vector-borne zoonosis in the northern hemisphere, and the pathogens causing Lyme borreliosis have distinct, incompletely described transmission cycles involving multiple host groups. The mammal community in Fennoscandia differs from continental Europe, and we have limited data on potential competent and incompetent hosts of the different genospecies of Borrelia burgdorferi sensu lato (sl) at the northern distribution ranges where Lyme borreliosis is emerging. We used qPCR to determine presence of B. burgdorferi sl in tissue samples (ear) from 16 mammalian species and questing ticks from Norway, and we sequenced the 5S-23 S rDNA intergenic spacer region to determine genospecies from 1449 qPCR-positive isolates obtaining 423 sequences. All infections coming from small rodents and shrews were linked to the genospecies B. afzelii, while B. burgdorferi sensu stricto (ss) was only found in red squirrels (Sciurus vulgaris). Red squirrels were also infected with B. afzelii and B. garinii. There was no evidence of B. burgdorferi sl infection in moose (Alces alces), red deer (Cervus elaphus) or roe deer (Capreolus capreolus), confirming the role of cervids as incompetent hosts. In infected questing ticks in the two western counties, B. afzelii (67% and 75%) dominated over B. garinii (27% and 21%) and with only a few recorded B. burgdorferi ss and B. valaisiana. B. burgdorferi ss were more common in adult ticks than in nymphs, consistent with a reservoir in squirrels. Our study identifies potential competent hosts for the different genospecies, which is key to understand transmission cycles at high latitudes of Europe.

Borrelia outer surface protein C is capable of human fibrinogen binding

Outer surface protein C (OspC) is one of the most abundant surface lipoproteins produced during early infection by the Borrelia spirochete, the causative agent of Lyme disease. The high sequence variability of the ospC gene results in the production of several and strongly divergent OspC types. One of the known roles of OspC is the recruitment of blood components, including complement regulators, to facilitate the bloodstream survival of Borrelia at an essential stage of host infection. Here, we identify and describe a new interaction between OspC and human fibrinogen. To test the ability of OspC to bind fibrinogen, we developed a microscale thermophoresis assay using four fluorescently labeled types of OspC. We show that OspC binds fibrinogen tightly, with nanomolar K_d , and that the binding depends on the OspC type. The binding assays combined with SAXS studies allowed us to map the OspC-binding site on the fibrinogen molecule. Spectrometric measurements of fibrinogen clotting in the presence of OspC indicate that OspC negatively influences the clot formation process. Taken together, our findings are consistent with the hypothesis that OspC interacts with blood protein partners to facilitate Borrelia spreading by the hematogenous route.

Emerging and threatening vector-borne zoonoses in the world and in Europe: a brief update

Climatic changes, landscape management, massive human, animal and commodity transportation represent important factors which are contributing to the spread of zoonotic diseases. The environmental and socioeconomic factors affecting the incidence of vector-borne zoonoses and possibilities for the reduction of disease impacts are discussed in the article. The most important zoonoses with expanding area of incidence and/or increasing occurrence are summarized, with special emphasis on the European region. While some diseases and their respective pathogens are indigenous to Europe (e.g. Lyme disease), others have been introduced to Europe from tropical areas (e.g. chikungunya or dengue fever). These emerging diseases may represent a serious threat in near future and better understanding of their spreading mechanisms, pathogenesis and consequent treatment is very important.

Infection prevalence and ecotypes of Anaplasma phagocytophilum in moose Alces alces, red deer Cervus elaphus, roe deer Capreolus capreolus and Ixodes ricinus ticks from Norway

Background

The geographical expansion of the tick Ixodes ricinus in northern Europe is a serious concern for animal and human health. The pathogen Anaplasma phagocytophilum is transmitted by ticks and causes emergences of tick-borne fever (anaplasmosis) in livestock. The transmission dynamics of the different ecotypes of A. phagocytophilum in the ecosystems is only partly determined. Red deer and roe deer contribute to circulation of different ecotypes of A. phagocytophilum in continental Europe, while the role of moose for circulation of different ecotypes is not fully established but an important issue in northern Europe.

Methods

We determined infection prevalence and ecotypes of A. phagocytophilum in moose (n = 111), red deer (n = 141), roe deer (n = 28) and questing ticks (n = 9241) in Norway.

Results

As previously described, red deer was exclusively linked to circulation of ecotype I, while roe deer was exclusively linked to circulation of ecotype II. Surprisingly, we found 58% ecotype I (n = 19) and 42% of ecotype II (n = 14) in moose. Both ecotypes were found in questing ticks in areas with multiple cervid species present, while only ecotype I was found in ticks in a region with only red deer present. Hence, the geographical distribution of ecotypes in ticks followed the distribution of cervid species present in a given region and their link to ecotype I and II.

Conclusions

Moose probably function as reservoirs for both ecotype I and II, indicating that the ecotypes of A. phagocytophilum are not entirely host-specific and have overlapping niches. The disease hazard depends also on both host abundance and the number of immature ticks fed by each host. Our study provides novel insights in the northern distribution and expansion of tick-borne fever.

An updated meta-analysis of the distribution and prevalence of Borrelia burgdorferi s.l. in ticks in Europe

Background

The bacteria of the group Borrelia burgdorferi s.l. are the etiological agents of Lyme borreliosis in humans, transmitted by bites of ticks. Improvement of control measures requires a solid framework of the environmental traits driving its prevalence in ticks.

Methods

We updated a previous meta-analysis of the reported prevalence of Borrelia burgdorferi s.l. in questing nymphs of Ixodes ricinus with a literature search from January 2010–June 2017. This resulted in 195 new papers providing the prevalence of Bb for 926 geo-referenced records. Previously obtained data (878 records, years 2000–2010) were appended for modelling. The complete dataset contains data from 82,004 questing nymphs, resulting in 558 records of B. afzelii, 404 of B. burgdorferi s.s. (only 80 after the year 2010), 552 of B. garinii, 78 of B. lusitaniae, 61 of B. spielmanii, and 373 of B. valaisiana. We associated the records with explicit coordinates to environmental conditions and to a categorical definition of European landscapes (LANMAP2) looking for a precise definition of the environmental niche of the most reported species of the pathogen, using models based on different classification methods.

Results

The most commonly reported species are B. afzelii, B. garinii and B. valaisiana largely overlapping across Europe. Prevalence in ticks is associated with portions of the environmental niche. Highest prevalence occurs in areas of 280°–290° (Kelvin) of mean annual temperature experiencing a small amplitude, steady spring slope, together with high mean values and a moderate spring rise of vegetation vigor. Low prevalence occurs in sites with low and a noteworthy annual amplitude of temperature and the Normalized Difference Vegetation Index (colder areas with abrupt annual changes of vegetation). Models based on support vector machines provided a correct classification rate of the habitat and prevalence of 89.5%. These results confirm the association of prevalence of the three most commonly reported species of B. burgdorferi s.l. in Europe to parts of the environmental niche and provide a statistically tractable framework for analyzing trends under scenarios of climate change.

Electronic supplementary material

The online version of this article (10.1186/s12942-018-0163-7) contains supplementary material, which is available to authorized users.

The importance of wildlife in the ecology and epidemiology of the TBE virus in Sweden: incidence of human TBE correlates with abundance of deer and hares

Background

Tick-borne encephalitis (TBE) is one tick-transmitted disease where the human incidence has increased in some European regions during the last two decades. We aim to find the most important factors causing the increasing incidence of human TBE in Sweden. Based on a review of published data we presume that certain temperature-related variables and the population densities of transmission hosts, i.e. small mammals, and of primary tick maintenance hosts, i.e. cervids and lagomorphs, of the TBE virus vector Ixodes ricinus, are among the potentially most important factors affecting the TBE incidence. Therefore, we compare hunting data of the major tick maintenance hosts and two of their important predators, and four climatic variables with the annual numbers of human cases of neuroinvasive TBE. Data for six Swedish regions where human TBE incidence is high or has recently increased are examined by a time-series analysis. Results from the six regions are combined using a meta-analytical method.

Results

With a one-year time lag, the roe deer (Capreolus capreolus), red deer (Cervus elaphus), mountain hare (Lepus timidus) and European hare (Lepus europaeus) showed positive covariance; the Eurasian elk (moose, Alces alces) and fallow deer (Dama dama) negative covariance; whereas the wild boar (Sus scrofa), lynx (Lynx lynx), red fox (Vulpes vulpes) and the four climate parameters showed no significant covariance with TBE incidence. All game species combined showed positive covariance.

Conclusions

The epidemiology of TBE varies with time and geography and depends on numerous factors, i.a. climate, virus genotypes, and densities of vectors, tick maintenance hosts and transmission hosts. This study suggests that the increased availability of deer to I. ricinus over large areas of potential tick habitats in southern Sweden increased the density and range of I. ricinus and created new TBEV foci, which resulted in increased incidence of human TBE. New foci may be established by TBE virus-infected birds, or by birds or migrating mammals infested with TBEV-infected ticks. Generally, persistence of TBE virus foci appears to require presence of transmission-competent small mammals, especially mice (Apodemus spp.) or bank voles (Myodes glareolus).

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3057-4) contains supplementary material, which is available to authorized users.

Ticks and Tick-Borne Infections: Complex Ecology, Agents, and Host Interactions

Ticks transmit the most diverse array of infectious agents of any arthropod vector. Both ticks and the microbes they transmit are recognized as significant threats to human and veterinary public health. This article examines the potential impacts of climate change on the distribution of ticks and the infections they transmit; the emergence of novel tick-borne pathogens, increasing geographic range and incidence of tick-borne infections; and advances in the characterization of tick saliva mediated modulation of host defenses and the implications of those interactions for transmission, establishment, and control of tick infestation and tick-borne infectious agents.

Tick abundance, pathogen prevalence, and disease incidence in two contrasting regions at the northern distribution range of Europe

Background

Emergence of tick-borne diseases is impacting humans and livestock across the Northern Hemisphere. There are, however, large regional variations in number of cases of tick-borne diseases. Some areas have surprisingly few cases of disease compared to other regions. The aim here is to provide a first step towards a better understanding of such contrasting regional patterns of disease emergences at the northern distribution range of Ixodes ricinus in Europe.

Methods

We compare disease incidence, vector abundance and pathogen prevalence in eastern and western Norway differing in the number of tick-borne disease cases. First, we analysed the incidence of Lyme borreliosis in humans, tick-borne fever (anaplasmosis) in sheep and anaplasmosis and babesiosis in cattle to verify if incidence differed. Secondly, we analysed extensive field data on questing tick density, pathogen prevalence, as well as the broad spatial pattern of human and livestock distribution as it may relate to tick exposure.

Results

The incidences of all diseases were lower in eastern, compared to western, Norway, but this was most marked for the livestock diseases. While the prevalence of Borrelia burgdorferi (sensu lato) in ticks was similar in the two regions, the prevalence of Anaplasma phagocytophilum was markedly lower in eastern, compared to western, Norway. We found overall a lower abundance of questing nymphs in the east. In the east, there were cases of babesiosis in cattle where anaplasmosis was absent, suggesting absence of the pathogen rather than differences in exposure to ticks as part of the explanation for the much lower incidence of anaplasmosis in eastern Norway.

Conclusions

Many factors contribute to different disease incidence across ecosystems. We found that regional variation in tick-borne disease incidence may be partly linked to vector abundance and pathogen prevalence, but differently for human and livestock diseases. Further studies are needed to determine if there is also regional variation in specific genospecies and strain frequencies differing in pathogenicity.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2890-9) contains supplementary material, which is available to authorized users.

Tick-borne encephalitis virus, Borrelia burgdorferi sensu lato, Borrelia miyamotoi, Anaplasma phagocytophilum and Candidatus Neoehrlichia mikurensis in Ixodes ricinus ticks collected from recreational islands in southern Norway

The aim of this study was to determine the occurrence of tick-borne pathogens of medical importance in questing ticks collected from five recreationally used islands along the Norwegian coastline. Furthermore, since coinfection may affect the disease severity, this study aimed to determine the extent of coinfection in individual ticks or co-localization of tick-borne pathogens. In all, 4158 questing Ixodes ricinus ticks were analyzed. For detection of tick-borne encephalitis virus (TBEV), nymphs (3690) were analyzed in pools of ten. To detect Borrelia burgdorferi sensu lato, B. miyamotoi, Anaplasma phagocytophilum and Candidatus Neoehrlichia mikurensis, 468 nymphs were analyzed individually. A total of five nymph pools was infected with TBEV, giving an overall prevalence of 0.14%. In the individually analyzed ticks, B. burgdorferi s. l. (15.6%), Candidatus N. mikurensis (11%), A. phagocytophilum (1.4%) and B. miyamotoi (0.9%) were detected. Coinfection was found in 3.3% of the ticks, and the only dual infection observed was with B. afzelii and Candidatus N. mikurensis. This association was significantly higher than what would occur by random chance.

Combining public participatory surveillance and occupancy modelling to predict the distributional response of Ixodes scapularis to climate change

Ixodes scapularis, a known vector of Borrelia burgdorferi sensu stricto (Bbss), is undergoing range expansion in many parts of Canada. The province of New Brunswick, which borders jurisdictions with established populations of I. scapularis, constitutes a range expansion zone for this species. To better understand the current and potential future distribution of this tick under climate change projections, this study applied occupancy modelling to distributional records of adult ticks that successfully overwintered, obtained through passive surveillance. This study indicates that I. scapularis occurs throughout the southern-most portion of the province, in close proximity to coastlines and major waterways. Milder winter conditions, as indicated by the number of degree days <0 °C, was determined to be a strong predictor of tick occurrence, as was, to a lesser degree, rising levels of annual precipitation, leading to a final model with a predictive accuracy of 0.845 (range: 0.828-0.893). Both RCP 4.5 and RCP 8.5 climate projections predict that a significant proportion of the province (roughly a quarter to a third) will be highly suitable for I. scapularis by the 2080s. Comparison with cases of canine infection show good spatial agreement with baseline model predictions, but the presence of canine Borrelia infections beyond the climate envelope, defined by the highest probabilities of tick occurrence, suggest the presence of Bbss-carrying ticks distributed by long-range dispersal events. This research demonstrates that predictive statistical modelling of multi-year surveillance information is an efficient way to identify areas where I. scapularis is most likely to occur, and can be used to guide subsequent active sampling efforts in order to better understand fine scale species distributional patterns.

Detecting the Lyme Disease Spirochete, Borrelia Burgdorferi, in Ticks Using Nested PCR

Lyme disease is a serious vector-borne infection that is caused by the Borrelia burgdorferi sensu lato family of spirochetes, which are transmitted to humans through the bite of infected Ixodes ticks. The primary etiological agent in North America is Borrelia burgdorferi sensu stricto. As geographic risk regions expand, it is prudent to support robust surveillance programs that can measure tick infection rates, and communicate findings to clinicians, veterinarians, and the general public. The molecular technique of nested polymerase chain reaction (nPCR) has long been used for this purpose, and it remains a central, inexpensive, and robust approach in the detection of Borrelia in both ticks and wildlife. This article demonstrates the application of nPCR to tick DNA extracts to identify infected specimens. Two independent B. burgdorferi targets, genes encoding Flagellin B (FlaB) and Outer surface protein A (OspA), have been used extensively with this technique. The protocol involves tick collection, DNA extraction, and then an initial round of PCR to detect each of the two Borrelia-specific loci. Subsequent polymerase chain reaction (PCR) uses the product of the first reaction as a new template to generate smaller, internal amplification fragments. The nested approach improves upon both the specificity and sensitivity of conventional PCR. A tick is considered positive for the pathogen when inner amplicons from both Borrelia genes can be detected by agarose gel electrophoresis.

Epidemiological investigation of Borrelia burgdorferi in horses in the municipality of Sinop-MT, Brazil

Borrelia burgdorferi sensu stricto is the main etiological agent of Lyme disease (LD) in the USA. In Brazil, it is believed that a similar spirochete is the causal agent of the Baggio-Yoshinari syndrome (BYS), a zoonosis also transmitted by ticks, whose clinical manifestations are similar to those of LD. Despite the epidemiological importance, there are no studies reporting the presence and the prevalence of B. burgdorferi among horses in Mato Grosso State. The aim of this study was to detect and measure the frequency of IgG antibodies anti-B. burgdorferi American strain G39/40 in horses in the municipality of Sinop, MT-Brazil, using the indirect enzyme-linked immunosorbent assay (ELISA) for serological diagnosis. Blood samples from 367 horses were collected in 81 farms. An epidemiological questionnaire was applied during the visits to obtain information related to the animals and the farms. From the 367 horses, 214 were positive for B. burgdorferi sensu stricto according to the results of the ELISA test, representing an apparent prevalence of 54.04% [CI = 0.4548051-0.6237234]. Concomitantly, 89 blood samples were taken for molecular analysis by nested polymerase chain reaction (PCR). According to the PCR test results, none of the samples were reactive, although 53 of these samples were reactive according to ELISA. Seventy five farms (92.59%) had at least one reactive horse for B. burgdorferi. Our results support the hypothesis of the presence of anti-Borrelia spp. antibodies in horses in Mato Grosso, reaching a high animal prevalence. Besides that, leisure/sport purposes proved to be a risk factor, with an odds ratio of 3.16. These findings clearly indicate the need of borreliosis control in Sinop and make a significant contribution to the knowledge of the disease in Mato Grosso.

A relapsing fever group Borrelia sp. is widely distributed among wild deer in Japan

A relapsing fever group Borrelia sp. was detected from the blood of wild deer (Cervus nippon) in Japan. The Borrelia sp. was distributed nationwide among deer with an overall prevalence of 26% in blood samples. The prevalence of infection was significantly higher in fawns (48.4%) compared to adult deer (23.6%). Sequencing analysis reveals that this Borrelia sp. belongs to the hard tick-borne relapsing fever borreliae, and that it forms a single lineage based on sequences of the flagellin and glycerophosphodiester phosphodiesterase genes. Borrelial genome copy number was estimated at 8.8 × 10³ genome copies/μl of blood. Other hard tick-borne relapsing fever borrelia (e.g. Borrelia miyamotoi) were not detected in deer blood in this study. These findings suggest that wild deer may act as reservoirs for this Borrelia sp. in Japan.

Molecular identification of Borrelia spirochetes in questing Ixodes ricinus from northwestern Spain

BACKGROUND

Ixodes ricinus, the predominant tick species in Europe, can transmit the causative agents of important human diseases such as Lyme borreliosis (LB), caused by Borrelia spirochetes. In northern Spain, LB is considered endemic; recently, a significant increase of the annual incidence of LB was reported in the northwestern (NW) region.

METHODS

In order to provide information on the prevalence of Borrelia spp., pooled and individually free-living I. ricinus from NW Spain were molecularly analyzed. Positive samples were characterized at the fla and Glpq genes and the rrfA-rrlB intergenic spacer region to identify Borrelia species/genospecies.

RESULTS

Borrelia burgdorferi (sensu lato) (s.l.) individual prevalence and MIR were significantly higher in adult females (32.3 and 16%) than in nymphs (18.8 and 6.2%) and adult males (15.6 and 8.4%). Five Borrelia genospecies belonging to the B. burgdorferi (s.l.) group were identified: B. garinii was predominant, followed by B. valaisiana, B. lusitaniae, B. afzelii and B. burgdorferi (sensu stricto) (s.s.). One species belonging to the tick-borne relapsing fever group (B. miyamotoi) was also found, showing low individual prevalence (1%), positive pool (0.7%) and MIR (0.1%) values. To our knowledge, this is the first citation of B. miyamotoi in free-living ticks from Spain.

CONCLUSIONS

The significant prevalences of B. burgdorferi (s.l.) genospecies detected in questing ticks from NW Spain are similar to those detected in northern and central European countries and higher to those previously found in Spain. These results together with the high incidence of LB in humans and the high seroprevalence of B. burgdorferi (s.l.) in roe deer shown in other studies reveal that the northwest area is one of the most risky regions for acquiring LB in Spain.

Host Distribution Does Not Limit the Range of the Tick Ixodes ricinus but Impacts the Circulation of Transmitted Pathogens

Ticks, pathogens, and vertebrates interact in a background of environmental features that regulate the densities of ticks and vertebrates, affecting their contact rates and thence the circulation of the pathogens. Regional scale studies are invaluable sources of information about the regulation of these interactions, but a large-scale analysis of the interaction of communities of ticks, hosts, and the environment has been never modeled. This study builds on network analysis, satellite-derived climate and vegetation, and environmental modeling, quantifying the interactions between the tick Ixodes ricinus and the transmitted bacteria of the complex Borrelia burgdorferi s.l. in the Western Palaearctic. We derived the rates of contact of the tick with 162 species of vertebrates recorded as hosts, and the relative importance of each vertebrate in the circulation of the pathogen. We compiled more than 11 millions of pairs of coordinates of the vertebrates, deriving distribution models of each species and the relative faunal composition in the target territory. The results of the modeling of the distribution of the tick and its hosts, weighted by their importance in the circulation of Borrelia captured the spatial patterns of interactions that allow the circulation of the pathogen. Results indicate that both I. ricinus and B. burgdorferi s.l. are supported in the Western Palaearctic by complex communities of vertebrates, which have large distribution ranges. This high functional redundancy results in the pervasiveness of B. burgdorferi s.l., which depends on the gradient of contributions of the large community of vertebrates, instead of relying on a few dominant vertebrates, which was the prevailing paradigm. Most prominent reservoirs of the pathogen are distributed in specific regions of the environmental niche. However, literally dozens of potential reservoirs can colonize many other environmental regions, marginally but efficiently contributing to the circulation of the pathogen. These results consistently point to the need of evaluating the beta-diversity of the community of vertebrates acting as reservoirs of the pathogen to better know the interactions with the vector. They also demonstrate why the pathogen is so resilient to perturbations in the composition of the reservoirs.

Immune escape strategies of Borrelia burgdorferi

The borrelial resurge demonstrates that Borrelia burgdorferi is a persistent health problem. This spirochete is responsible for a global public health concern called Lyme disease. B. burgdorferi faces diverse environmental conditions of its vector and host during its life cycle. To circumvent the host immune system is a prominent feature of B. burgdorferi. To date, numerous studies have reported on the various mechanisms used by this pathogen to evade the host defense mechanisms. This current review attempts to consolidate this information to describe the immunological and molecular methods used by B. burgdorferi for its survival.

Evidence for genetic hybridization between Ixodes scapularis and Ixodes cookei

Ixodes scapularis Say, 1821 (the black-legged tick) is becoming established in Canada. The northwards expansion of I. scapularis leads to contact between I. scapularis and Ixodes cookei Packard, 1869, a well-established tick species in Eastern Canada. Examination of I. cookei and I. scapularis collected from New Brunswick revealed ticks with ambiguous morphologies, with either a mixture or intermediate traits typical of I. scapularis and I. cookei, including in characteristics typically used as species identifiers. Genetic analysis to determine if these ticks represent hybrids revealed that four had I. cookei derived mitochondrial DNA but I. scapularis nuclear DNA. In one case, the nuclear sequence showed evidence of heterozygosity for I. scapularis and I. cookei sequences, whereas in the others, the nuclear DNA appeared to be entirely derived from I. scapularis. These data strongly suggest genetic hybridization between these two species. Ixodes cookei and hybrid ticks were readily collected from humans and companion animals and specimens infected with Borrelia burgdorferi Johnson et al., 1984, the causative agent of Lyme disease, were identified. These findings raise the issue of genetic introgression of I. scapularis genes into I. cookei and warrant reassessment of the capacity of I. cookei and I. cookei × I. scapularis hybrids to vector Borrelia infection.

Effective methods for tick removal: A systematic review

AIM

Providing evidence-based first aid training to lay people is a cost-effective intervention. This systematic review aimed to collect the best available evidence on effective methods to remove a tick, performed by lay people.

METHODS

A systematic search was performed searching the Cochrane Library (via Wiley), MEDLINE (via the PubMed interface), and Embase (via the Embase.com interface) to identify studies with evidence on tick removal strategies. Study selection was performed by two independent reviewers and data extraction was achieved in a tabular format. GRADE was used to determine the quality of evidence.

RESULTS

Out of 2046 articles, six experimental animal studies were included. These studies compared different chemical treatments (gasoline, petroleum jelly, clear fingernail polish, or methylated spirit) or mechanical techniques (forceps or commercial devices) for tick removal. The available studies were all of very low quality and suggest that there is limited evidence in favor of pulling with commercial devices and in favor of pulling with forceps compared to rotation with forceps to remove ticks.

CONCLUSIONS

Limited evidence was found in favor of pulling with commercial tick removal devices or pulling with forceps. The evidence of the included studies is of very low quality and results of these studies are imprecise due to limited sample size, large variability of results, and/or lack of data. Since large high-quality studies are lacking, more rigorous studies are warranted to enable strong evidence-based recommendations.

Tick surveillance for Borrelia miyamotoi and phylogenetic analysis of isolates in Mongolia and Japan

Borrelia miyamotoi, recently recognized as a human pathogenic spirochete, was isolated from Ixodes persulcatus and I. ovatus in northern Mongolia and Honshu Island, a major island in Japan. Although no human B. miyamotoi infections have been reported in Mongolia, the prevalence of B. miyamotoi in ticks from Mongolia is higher than that in ticks from Hokkaido, Japan, where human cases have been reported. Moreover, the multi-locus sequence analysis of cultured isolates revealed that B. miyamotoi isolates in Mongolia belong to the Siberian type, a sequence type that was originally reported from isolates from I. persulcatus in Hokkaido. Thus, there is a possibility of unrecognized human B. miyamotoi infections in Mongolia. Moreover our data support the hypothesis of clonal expansion of the Siberian type B. miyamotoi. In contrast, although the isolates were found to belong to the Siberian type B. miyamotoi, two isolates from I. persulcatus in Honshu Island were identified to be of a different sequence type. Furthermore, B. miyamotoi isolates from I. ovatus were distinguishable from those from I. ricinus complex ticks, according to genetic analysis. In this study, we show that there may be some genetic diversity among B. miyamotoi in ticks from Honshu Island.