Global ecology and epidemiology of Borrelia garinii spirochetes

Tick-Borne Bacterial Diseases in Europe: Threats to public health

BACKGROUND

Tick-borne diseases, caused by bacterial pathogens, pose a growing threat to public health in Europe. This paper provides an overview of the historical context of the discovery of the most impactful pathogens transmitted by ticks, including Borrelia burgdorferi sensu lato, Rickettsia spp., Anaplasma spp., Francisella spp., Ehrlichia spp., and Neoehrlichia mikurensis. Understanding the historical context of their discovery provides insight into the evolution of our understanding of these pathogens.

METHODS AND RESULTS

Systematic investigation of the prevalence and transmission dynamics of these bacterial pathogens is provided, highlighting the intricate relationships among ticks, host organisms, and the environment. Epidemiology is explored, providing an in-depth analysis of clinical features associated with infections. Diagnostic methodologies undergo critical examination, with a spotlight on technological advancements that enhance detection capabilities. Additionally, the paper discusses available treatment options, addressing existing therapeutic strategies and considering future aspects.

CONCLUSIONS

By integrating various pieces of information on these bacterial species, the paper aims to provide a comprehensive resource for researchers and healthcare professionals addressing the impact of bacterial tick-borne diseases in Europe. This review underscores the importance of understanding the complex details influencing bacterial prevalence and transmission dynamics to better combat these emerging public health threats.

Unprecedented genetic variability of PFam54 paralogs among Eurasian Lyme borreliosis-causing spirochetes

Lyme borreliosis (LB) is the most common vector-borne disease in the Northern Hemisphere caused by spirochetes belonging to the Borrelia burgdorferi sensu lato (Bbsl) complex. Borrelia spirochetes circulate in obligatory transmission cycles between tick vectors and different vertebrate hosts. To successfully complete this complex transmission cycle, Bbsl encodes for an arsenal of proteins including the PFam54 protein family with known, or proposed, influences to reservoir host and/or vector adaptation. Even so, only fragmentary information is available regarding the naturally occurring level of variation in the PFam54 gene array especially in relation to Eurasian-distributed species. Utilizing whole genome data from isolates (n = 141) originated from three major LB-causing Borrelia species across Eurasia (B. afzelii, B. bavariensis, and B. garinii), we aimed to characterize the diversity of the PFam54 gene array in these isolates to facilitate understanding the evolution of PFam54 paralogs on an intra- and interspecies level. We found an extraordinarily high level of variation in the PFam54 gene array with 39 PFam54 paralogs belonging to 23 orthologous groups including five novel paralogs. Even so, the gene array appears to have remained fairly stable over the evolutionary history of the studied Borrelia species. Interestingly, genes outside Clade IV, which contains genes encoding for proteins associated with Borrelia pathogenesis, more frequently displayed signatures of diversifying selection between clades that differ in hypothesized vector or host species. This could suggest that non-Clade IV paralogs play a more important role in host and/or vector adaptation than previously expected, which would require future lab-based studies to validate.

Detection, identification and genotyping of Borrelia spp. in ticks of Coastal-Karst and Littoral-Inner Carniola regions in Slovenia

The density and spread of tick vector species have increased throughout Europe in the last 30 years, leading to an increase of Lyme borreliosis cases, including in Slovenia. The aim of this study was to isolate Borrelia strains and determine the prevalence of B. burgdorferi sensu lato and B. miyamotoi in adults of Ixodes ricinus (Linnaeus) collected in 2019 in the two regions of the country (Coastal-Karst and Littoral-Inner Carniola) by cultivation and PCR. We isolated B. burgdorferi s.l. by culture method in 28/559 (5%) ticks from both regions. Culture-negative samples (531/559, i.e., 95%) were additionally tested by real-time PCR. In 155/531 (29.2%) PCR-positive samples, a fragment of flaB or glpQ was amplified and further sequenced to identify species of the Borrelia. Using both methods, cultivation and PCR, Borrelia spp. prevalence was 32.7% in the Coastal-Karst region and 33.0% in the Littoral-Inner Carniola region. Genotyping of the Borrelia spp. isolates revealed that 17/28 (60%) were B. garinii subtype Mlg2. Of all tick samples tested for B. miyamotoi 8/398 (2%) were PCR positive. Based on previous studies in these regions, we had expected more ticks to be infected with B. afzelii, but genotyping revealed that B. garinii was the most abundant.

Out of Asia? Expansion of Eurasian Lyme borreliosis causing genospecies display unique evolutionary trajectories

Vector-borne pathogens exist in obligate transmission cycles between vector and reservoir host species. Host and vector shifts can lead to geographic expansion of infectious agents and the emergence of new diseases in susceptible individuals. Three bacterial genospecies (Borrelia afzelii, Borrelia bavariensis, and Borrelia garinii) predominantly utilize two distinct tick species as vectors in Asia (Ixodes persulcatus) and Europe (Ixodes ricinus). Through these vectors, the bacteria can infect various vertebrate groups (e.g., rodents, birds) including humans where they cause Lyme borreliosis, the most common vector-borne disease in the Northern hemisphere. Yet, how and in which order the three Borrelia genospecies colonized each continent remains unclear including the evolutionary consequences of this geographic expansion. Here, by reconstructing the evolutionary history of 142 Eurasian isolates, we found evidence that the ancestors of each of the three genospecies probably have an Asian origin. Even so, each genospecies studied displayed a unique substructuring and evolutionary response to the colonization of Europe. The pattern of allele sharing between continents is consistent with the dispersal rate of the respective vertebrate hosts, supporting the concept that adaptation of Borrelia genospecies to the host is important for pathogen dispersal. Our results highlight that Eurasian Lyme borreliosis agents are all capable of geographic expansion with host association influencing their dispersal; further displaying the importance of host and vector association to the geographic expansion of vector-borne pathogens and potentially conditioning their capacity as emergent pathogens.

Genomic Confirmation of Borrelia garinii, United States

Lyme disease is a multisystem disorder primarily caused by Borrelia burgdorferi sensu lato. However, B. garinii, which has been identified on islands off the coast of Newfoundland and Labrador, Canada, is a cause of Lyme disease in Eurasia. We report isolation and whole-genome nucleotide sequencing of a B. garinii isolate from a cotton mouse (Peromyscus gossypinus) in South Carolina, USA. We identified a second B. garinii isolate from the same repository. Phylogenetic analysis does not associate these isolates with the previously described isolates of B. garinii from Canada.

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.

The Population Structure of Borrelia lusitaniae Is Reflected by a Population Division of Its Ixodes Vector

Populations of vector-borne pathogens are shaped by the distribution and movement of vector and reservoir hosts. To study what impact host and vector association have on tick-borne pathogens, we investigated the population structure of Borrelia lusitaniae using multilocus sequence typing (MLST). Novel sequences were acquired from questing ticks collected in multiple North African and European locations and were supplemented by publicly available sequences at the Borrelia Pubmlst database (accessed on 11 February 2020). Population structure of B. lusitaniae was inferred using clustering and network analyses. Maximum likelihood phylogenies for two molecular tick markers (the mitochondrial 16S rRNA locus and a nuclear locus, Tick-receptor of outer surface protein A, trospA) were used to confirm the morphological species identification of collected ticks. Our results confirmed that B. lusitaniae does indeed form two distinguishable populations: one containing mostly European samples and the other mostly Portuguese and North African samples. Of interest, Portuguese samples clustered largely based on being from north (European) or south (North African) of the river Targus. As two different Ixodes species (i.e., I. ricinus and I. inopinatus) may vector Borrelia in these regions, reference samples were included for I. inopinatus but did not form monophyletic clades in either tree, suggesting some misidentification. Even so, the trospA phylogeny showed a monophyletic clade containing tick samples from Northern Africa and Portugal south of the river Tagus suggesting a population division in Ixodes on this locus. The pattern mirrored the clustering of B. lusitaniae samples, suggesting a potential co-evolution between tick and Borrelia populations that deserve further investigation.

Multi-country investigation of the diversity and associated microorganisms isolated from tick species from domestic animals, wildlife and vegetation in selected african countries

In many areas of Africa, recent studies highlighted the great impact of ticks on animal and human health throughout the continent. On the other hand, very limited information on the bacterial endosymbionts of the African ticks and their pattern of co-infections with other bacteria are found in literature, notwithstanding their pivotal role in tick survival and vector efficiency. Thus, we investigated the distribution of selected pathogenic and symbiotic bacteria in hard ticks collected from wild, domestic animals and from vegetation in various ecological zones in Africa and their co-occurrence in the same tick host. Overall, 339 hard ticks were morphologically identified as belonging to the genera Amblyomma, Dermacentor, Hyalomma, Haemaphysalis, Ixodes and Rhipicephalus. Molecular screening provided information on pathogens circulation in Africa, detecting spotted fever group rickettsiae, Anaplasma spp., Ehrlichia ruminantium, Borrelia garinii, Babesia spp., Theileria spp. and Coxiella burnetii. Furthermore, our work provides insights on the African scenario of tick-symbiont associations, revealing the presence of Coxiella, Francisella and Midichloria across multiple tick populations. Coxiella endosymbionts were the most prevalent microorganisms, and that with the broadest spectrum of hosts, being detected in 16 tick species. Francisella was highly prevalent among the Hyalomma species tested and correlated negatively with the presence of Coxiella, showing a potential competitive interaction. Interestingly, we detected a positive association of Francisella with Rickettsia in specimens of Hy. rufipes, suggesting a synergistic interaction between them. Finally, Midichloria was the most prevalent symbiont in Rhipicephalus sanguineus sensu lato from Egypt.

Mapping ticks and tick-borne pathogens in China

Understanding ecological niches of major tick species and prevalent tick-borne pathogens is crucial for efficient surveillance and control of tick-borne diseases. Here we provide an up-to-date review on the spatial distributions of ticks and tick-borne pathogens in China. We map at the county level 124 tick species, 103 tick-borne agents, and human cases infected with 29 species (subspecies) of tick-borne pathogens that were reported in China during 1950-2018. Haemaphysalis longicornis is found to harbor the highest variety of tick-borne agents, followed by Ixodes persulcatus, Dermacentor nutalli and Rhipicephalus microplus. Using a machine learning algorithm, we assess ecoclimatic and socioenvironmental drivers for the distributions of 19 predominant vector ticks and two tick-borne pathogens associated with the highest disease burden. The model-predicted suitable habitats for the 19 tick species are 14‒476% larger in size than the geographic areas where these species were detected, indicating severe under-detection. Tick species harboring pathogens of imminent threats to public health should be prioritized for more active field surveillance.

Lyme Disease in Humans

Lyme disease (Lyme borreliosis) is a tick-borne, zoonosis of adults and children caused by genospecies of the Borrelia burgdorferi sensu lato complex. The ailment, widespread throughout the Northern Hemisphere, continues to increase globally due to multiple environmental factors, coupled with increased incursion of humans into habitats that harbor the spirochete. B. burgdorferi sensu lato is transmitted by ticks from the Ixodes ricinus complex. In North America, B. burgdorferi causes nearly all infections; in Europe, B. afzelii and B. garinii are most associated with human disease. The spirochete's unusual fragmented genome encodes a plethora of differentially expressed outer surface lipoproteins that play a seminal role in the bacterium's ability to sustain itself within its enzootic cycle and cause disease when transmitted to its incidental human host. Tissue damage and symptomatology (i.e., clinical manifestations) result from the inflammatory response elicited by the bacterium and its constituents. The deposition of spirochetes into human dermal tissue generates a local inflammatory response that manifests as erythema migrans (EM), the hallmark skin lesion. If treated appropriately and early, the prognosis is excellent. However, in untreated patients, the disease may present with a wide range of clinical manifestations, most commonly involving the central nervous system, joints, or heart. A small percentage (~10%) of patients may go on to develop a poorly defined fibromyalgia-like illness, post-treatment Lyme disease (PTLD) unresponsive to prolonged antimicrobial therapy. Below we integrate current knowledge regarding the ecologic, epidemiologic, microbiologic, and immunologic facets of Lyme disease into a conceptual framework that sheds light on the disorder that healthcare providers encounter.

Evolutionary ecology of Lyme Borrelia

The bacterial genus, Borrelia, is comprised of vector-borne spirochete species that infect and are transmitted from multiple host species. Some Borrelia species cause highly-prevalent diseases in humans and domestic animals. Evolutionary, ecological, and molecular research on many Borrelia species have resulted in tremendous progress toward understanding the biology and natural history of these species. Yet, many outstanding questions, such as how Borrelia populations will be impacted by climate and land-use change, will require an interdisciplinary approach. The evolutionary ecology research framework incorporates theory and data from evolutionary, ecological, and molecular studies while overcoming common assumptions within each field that can hinder integration across these disciplines. Evolutionary ecology offers a framework to evaluate the ecological consequences of evolved traits and to predict how present-day ecological processes may result in further evolutionary change. Studies of microbes with complex transmission cycles, like Borrelia, which interact with multiple vertebrate hosts and arthropod vectors, are poised to leverage the power of the evolutionary ecology framework to identify the molecular interactions involved in ecological processes that result in evolutionary change. Using existing data, we outline how evolutionary ecology theory can delineate how interactions with other species and the physical environment create selective forces or impact migration of Borrelia populations and result in micro-evolutionary changes. We further discuss the ecological and molecular consequences of those micro-evolutionary changes. While many of the currently outstanding questions will necessitate new experimental designs and additional empirical data, many others can be addressed immediately by integrating existing molecular and ecological data within an evolutionary ecology framework.

Epidemiological Characteristics of Field Tick-Borne Pathogens in Gwang-ju Metropolitan Area, South Korea, from 2014 to 2018

Objectives

The importance of tick-borne diseases is increasing because of climate change, with a lack of long-term studies on tick-borne pathogens in South Korea. To understand the epidemiological characteristics of tick-borne diseases, the monthly distribution of field ticks throughout the year was studied in South Korea between May 2014 and April 2018 in a cross sectional study.

Methods

The presence of various tick-borne pathogens (Rickettsia species, Borrelia species, Anaplasma phagocytophilum) was confirmed by using polymerase chain reaction, to provide information for a prevention strategy against tick-borne pathogenic infections, through increased understanding of the relationship between seasonal variation and risk of infection with Rickettsia species. This was performed using logistic regression analysis (SPSS 20, IBM, USA) of the data obtained from the study.

Results

During the study period there were 11,717 ticks collected and 4 species identified. Haemapysalis longicornis was the most common species (n = 10,904, 93.1%), followed by Haemapysalis flava (n = 656, 5.6%), Ixodes nipponensis (n = 151, 1.3%), and Amblyomma testudinarium (n = 6, 0.05%) The results of this cross-sectional study showed that Haemapysalis flava carried a higher risk of transmission of Rickettsia species than other tick species (p < 0.05).

Conclusion

In conclusion, due attention should be paid to preventing tick-borne infections in humans whilst engaged in outdoor activities in Spring and Autumn, particularly in places where there is a high prevalence of ticks.

Longitudinal study of prevalence and spatio-temporal distribution of Borrelia burgdorferi sensu lato in ticks from three defined habitats in Latvia, 1999-2010

Members of the Borrelia burgdorferi sensu lato (s.l.) species complex are known to cause human Lyme borreliosis. Because of longevity of some reservoir hosts and the Ixodes tick vectors' life cycle, long-term studies are required to better understand species and population dynamics of these bacteria in their natural habitats. Ticks were collected between 1999 and 2010 in three ecologically different habitats in Latvia. We used multilocus sequence typing utilizing eight chromosomally located housekeeping genes to obtain information about species and population fluctuations and/or stability of B. burgdorferi s.l. in these habitats. The average prevalence over all years was 18.9%. From initial high-infection prevalences of 25.5%, 33.1% and 31.8%, from 2002 onwards the infection rates steadily decreased to 7.3%. Borrelia afzelii and Borrelia garinii were the most commonly found genospecies but striking local differences were obvious. In one habitat, a significant shift from rodent-associated to bird-associated Borrelia species was noted whilst in the other habitats, Borrelia species composition was relatively stable over time. Sequence types (STs) showed a random spatial and temporal distribution. These results demonstrated that there are temporal regional changes and extrapolations from one habitat to the next are not possible.

Host dispersal shapes the population structure of a tick-borne bacterial pathogen

Birds are hosts for several zoonotic pathogens. Because of their high mobility, especially of longdistance migrants, birds can disperse these pathogens, affecting their distribution and phylogeography. We focused on Borrelia burgdorferi sensu lato, which includes the causative agents of Lyme borreliosis, as an example for tick-borne pathogens, to address the role of birds as propagation hosts of zoonotic agents at a large geographical scale. We collected ticks from passerine birds in 11 European countries. B. burgdorferi s.l. prevalence in Ixodes spp. was 37% and increased with latitude. The fieldfare Turdus pilaris and the blackbird T. merula carried ticks with the highest Borrelia prevalence (92 and 58%, respectively), whereas robin Erithacus rubecula ticks were the least infected (3.8%). Borrelia garinii was the most prevalent genospecies (61%), followed by B. valaisiana (24%), B. afzelii (9%), B. turdi (5%) and B. lusitaniae (0.5%). A novel Borrelia genospecies "Candidatus Borrelia aligera" was also detected. Multilocus sequence typing (MLST) analysis of B. garinii isolates together with the global collection of B. garinii genotypes obtained from the Borrelia MLST public database revealed that: (a) there was little overlap among genotypes from different continents, (b) there was no geographical structuring within Europe, and (c) there was no evident association pattern detectable among B. garinii genotypes from ticks feeding on birds, questing ticks or human isolates. These findings strengthen the hypothesis that the population structure and evolutionary biology of tick-borne pathogens are shaped by their host associations and the movement patterns of these hosts.

Bacterial microbiota composition of Ixodes ricinus ticks: the role of environmental variation, tick characteristics and microbial interactions

Ecological factors, host characteristics and/or interactions among microbes may all shape the occurrence of microbes and the structure of microbial communities within organisms. In the past, disentangling these factors and determining their relative importance in shaping within-host microbiota communities has been hampered by analytical limitations to account for (dis)similar environmental preferences ('environmental filtering'). Here we used a joint species distribution modelling (JSDM) approach to characterize the bacterial microbiota of one of the most important disease vectors in Europe, the sheep tick Ixodes ricinus, along ecological gradients in the Swiss Alps. Although our study captured extensive environmental variation along elevational clines, the explanatory power of such large-scale ecological factors was comparably weak, suggesting that tick-specific traits and behaviours, microhabitat and -climate experienced by ticks, and interactions among microbes play an important role in shaping tick microbial communities. Indeed, when accounting for shared environmental preferences, evidence for significant patterns of positive or negative co-occurrence among microbes was found, which is indicative of competition or facilitation processes. Signals of facilitation were observed primarily among human pathogens, leading to co-infection within ticks, whereas signals of competition were observed between the tick endosymbiont Spiroplasma and human pathogens. These findings highlight the important role of small-scale ecological variation and microbe-microbe interactions in shaping tick microbial communities and the dynamics of tick-borne disease.

A cross-sectional study of small mammals for tick-borne pathogen infection in northern Mongolia

Background: Tick-borne pathogens (TBPs) are frequently studied in developed nations but are often neglected in emerging countries. In Mongolia, TBP research is especially sparse, with few research reports focusing upon human and domestic animal disease and tick ecology. However, little information exists on TBPs in small mammals. Methods: In this 2016 cross-sectional pilot study, we sought to uniquely study wildlife for TBPs. We live-trapped small mammals, and tested their whole blood, serum and ear biopsy samples for molecular or serological evidence of Borrelia spp., Rickettsia spp., and Anaplasma spp./Ehrlichia spp. Results: Of 64 small mammals collected, 56.0%, 39.0% and 0.0% of animals were positive by molecular assays for Borrelia spp., Rickettsia spp., and Anaplasma spp./Erhlicia spp., respectively. 41.9% were seropositive for A. phagocytophilum and 24.2% of animals were seropositive for Rickettsia rickettsii. Conclusion: This pilot data demonstrates evidence of a number of TBPs among small mammal populations in northern Mongolia and suggests the need to further investigate what role these mammals play in human and domestic animal disease.

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’.

Ticks and the city - are there any differences between city parks and natural forests in terms of tick abundance and prevalence of spirochaetes?

BACKGROUND

Ixodes ricinus ticks are commonly encountered in either natural or urban areas, contributing to Lyme disease agents Borreliella [(Borrelia burgdorferi (sensu lato)] spp. and Borrelia miyamotoi enzootic cycles in cities. It is an actual problem whether urbanization affects pathogen circulation and therefore risk of infection. The aim of the study was to evaluate main tick-borne disease risk factors in natural, endemic areas of north-east (NE) Poland (Białowieża) and urban areas of central Poland (Warsaw), measuring tick abundance/density, prevalence of infection with spirochaetes and diversity of these pathogens in spring-early summer and late summer-autumn periods between 2012 and 2015.

METHODS

Questing I. ricinus ticks were collected from three urban sites in Warsaw, central Poland and three natural sites in Białowieża, NE Poland. A total of 2993 ticks were analyzed for the presence of Borreliella spp. and/or Borrelia miyamotoi DNA by PCR. Tick abundance was analyzed by General Linear Models (GLM). Prevalence and distribution of spirochaetes was analyzed by Maximum Likelihood techniques based on log-linear analysis of contingency tables (HILOGLINEAR). Species typing and molecular phylogenetic analysis based on the sequenced flaB marker were carried out.

RESULTS

Overall 4617 I. ricinus ticks were collected (2258 nymphs and 2359 adults). We report well established population of ticks in urban areas (10.1 ± 0.9 ticks/100 m²), as in endemic natural areas with higher mean tick abundance (16.5 ± 1.5 ticks/100 m²). Tick densities were the highest in spring-early summer in both types of areas. We observed no effect of the type of area on Borreliella spp. and B. miyamotoi presence in ticks, resulting in similar prevalence of spirochaetes in urban and natural areas [10.9% (95% CI: 9.7-12.2%) vs 12.4% (95% CI: 10.1-15.1%), respectively]. Prevalence of spirochaetes was significantly higher in the summer-autumn period than in the spring-early summer [15.0% (95% CI: 12.8-17.5%) vs 10.4% (95% CI: 9.2-11.6%), respectively]. We have detected six species of bacteria present in both types of areas, with different frequencies: dominance of B. afzelii (69.3%) in urban and B. garinii (48.1%) in natural areas. Although we observed higher tick densities in forests than in maintained parks, the prevalence of spirochaetes was significantly higher in the latter [9.8% (95% CI: 8.6-11.0%) vs 17.5% (95% CI: 14.4-20.5%)].

CONCLUSIONS

Surprisingly, a similar risk of infection with Borreliella spp. and/or B. miyamotoi was discovered in highly- and low-transformed areas. We suggest that the awareness of presence of these disease agents in cities should be raised.

Prevalencia de Borrelia burgdorferi sensu lato en roedores sinantrópicos de dos comunidades rurales de Yucatán, México

<p><strong>Introducción.</strong> La enfermedad de Lyme es una zoonosis multisistémica causada por Borrelia burgdorferi sensu lato. Esta espiroqueta circula en un ciclo enzoótico entre un reservorio vertebrado primario y las garrapatas. Diferentes especies de roedores están identificadas por ser eficientes reservorios naturales para B. burgdorferi s.l.</p><p><strong>Objetivo.</strong> Estimar la prevalencia de B. burgdorferi s.l. en roedores sinantrópicos empleando dos comunidades rurales de Yucatán, México.</p><p><strong>Materiales y métodos.</strong> Se capturaron 123 roedores (94 Mus musculus y 29 Rattus rattus) para obtener muestras de tejidos de oreja y vejiga. Para detectar la presencia de B. burgdorferi s.l. en la muestras, se amplificaron los genes de la flagelina B (fla B) y las lipoproteínas de membrana externa, ospC y p66, empleado la reacción en cadena de la polimerasa. Los amplicones obtenidos fueron secuenciados.</p><p><strong>Resultados.</strong> La frecuencia de infección de B. burgdorferi s.l. en roedores fue de 36,5% para flaB (45/123), 10,5% (13/123) para p66 y 3,2% (4/123) para ospC. R. rattus tuvo una frecuencia de infección de 17,2% y M. musculus de 42,5%. La frecuencia de infección de B. burgdorferi s.l. en los tejidos estudiados fue de 11,3% (14/123) en vejigas y 17,0% (21/123) en orejas. No se encontraron diferencias estadísticas (p &gt; 0,05) en la frecuencia de infección entre las dos muestras de tejido utilizadas para el diagnóstico. El gen ospC presentó un 98% de homología con la especie  Borrelia garinii, una de las especies heterogéneas del complejo B. burgdorferi s.l.</p><p> </p><p><strong>Conclusiones.</strong> Se concluye que los roedores presentan alta prevalencia de infección con B. burgdorferi s.l., y ambas especies, M. musculus y R. rattus, podrían estar jugando un papel importante en el mantenimiento de esta bacteria en comunidades rurales de Yucatán, México.</p><pre style="line-height: 200%; background-image: initial; background-attachment: initial; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"><strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES">Introducción.</span></strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES"> La enfermedad de Lyme es una zoonosis multisistémica causada por <em>Borrelia burgdorferi</em> sensu lato. Esta espiroqueta circula en un ciclo enzoótico entre un reservorio vertebrado primario y las garrapatas. Diferentes especies de roedores están identificadas por ser eficientes reservorios naturales para <em>B. burgdorferi</em> s.l.</span></pre><pre style="line-height: 200%; background-image: initial; background-attachment: initial; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"><strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES">Objetivo.</span></strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES"> Estimar la prevalencia de <em>B. burgdorferi</em> s.l. en roedores sinantrópicos empleando dos comunidades rurales de Yucatán, México.</span></pre><pre style="line-height: 200%; background-image: initial; background-attachment: initial; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"><strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES">Materiales y métodos.</span></strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES"> Se capturaron 123 roedores (94 <em>Mus musculus</em> y 29 <em>Rattus rattus</em>) para obtener muestras de tejidos de oreja y vejiga. Para detectar la presencia de<em> B. burgdorferi</em> s.l. en la muestras, se amplificaron los genes de la flagelina B (<em>fla B</em>) y las lipoproteínas de membrana externa, <em>ospC</em> y <em>p66</em>, empleado la reacción en cadena de la polimerasa. Los amplicones obtenidos fueron secuenciados.</span></pre><pre style="line-height: 200%; background-image: initial; background-attachment: initial; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"><strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES">Resultados.</span></strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES"> La frecuencia de infección de <em>B. burgdorferi</em> s.l. en roedores fue de 36,5% para <em>flaB</em> (45/123), 10,5% (13/123) para <em>p66 </em>y 3,2% (4/123) para <em>ospC</em>. <em>R. rattus</em> tuvo una frecuencia de infección de 17,2% y <em>M. musculus</em> de 42,5%. La frecuencia de infección de <em>B. burgdorferi</em> s.l. en los tejidos estudiados fue de 11,3% (14/123) en vejigas y 17,0% (21/123) en orejas. No se encontraron diferencias estadísticas (p &gt; 0,05) en la frecuencia de infección entre las dos muestras de tejido utilizadas para el diagnóstico. El gen <em>ospC</em> presentó un 98% de homología con la especie  <em>Borrelia garinii, </em>una de las especies heterogéneas del complejo<em> B. burgdorferi s.l</em>.</span></pre><pre style="line-height: 200%; background-image: initial; background-attachment: initial; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"><strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES">Conclusiones.</span></strong><span style="font-size: 12.0pt; line-height: 200%; font-family: 'Arial',sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: ES-MX;" lang="ES"> Se concluye que los roedores presentan alta prevalencia de infección con <em>B. burgdorferi</em> s.l., y ambas especies, <em>M. musculus</em> y <em>R. rattus, </em>podrían estar jugando un papel importante en el mantenimiento de esta bacteria en comunidades rurales de Yucatán, México.<strong></strong></span></pre>

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.

Exploring Diversity among Norwegian Borrelia Strains Originating from Ixodes ricinus Ticks

Characterisation of Borrelia strains from Ixodes ricinus ticks is important in the epidemiological surveillance of vector-borne pathogens. Multilocus sequences analysis (MLSA) is a molecular genotyping tool with high discriminatory power that has been applied in evolutionary studies and for the characterisation of Borrelia genospecies. MLSA was used to study genetic variations in Borrelia strains isolated from I. ricinus ticks collected from the woodlands in Skodje. The results demonstrate that the 50 Borrelia strains were separated into 36 sequence types (STs) that were not previously represented in the MLST database. A distance matrix neighbour-joining tree (bootstrapped 500 iterations) showed four deeply branched clusters, and each deeply branched cluster represented one Borrelia genospecies. The mean pairwise genetic differences confirm the genospecies clustering. The combination of alleles separates the Borrelia strains from northwest Norway from the strains in the MLST database, thus identifying new STs. Although a highly divergent B. afzelii population could be expected, the heterogeneity among the B. garinii strains is more unusual. The present study indicates that the circulation of strains between migrating birds and stationary birds in this coastal region may play a role in the evolution of B. garinii strains.

Diversity of Rickettsiales in the microbiome of the lone star tick, Amblyomma americanum

Ticks are important vectors for many emerging pathogens. However, they are also infected with many symbionts and commensals, often competing for the same niches. In this paper, we characterize the microbiome of Amblyomma americanum (Acari: Ixodidae), the lone star tick, in order to better understand the evolutionary relationships between pathogens and nonpathogens. Multitag pyrosequencing of prokaryotic 16S rRNA genes (16S rRNA) was performed on 20 lone star ticks (including males, females, and nymphs). Pyrosequencing of the rickettsial sca0 gene (also known as ompA or rompA) was performed on six ticks. Female ticks had less diverse microbiomes than males and nymphs, with greater population densities of Rickettsiales. The most common members of Rickettsiales were "Candidatus Rickettsia amblyommii" and "Candidatus Midichloria mitochondrii." "Ca. Rickettsia amblyommii" was 2.6-fold more common in females than males, and there was no sequence diversity in the sca0 gene. These results are consistent with a predominantly vertical transmission pattern for "Ca. Rickettsia amblyommii."

Diversity and function of the avian gut microbiota

The intestinal microbiota have now been shown to largely affect host health through various functional roles in terms of nutrition, immunity, and other physiological systems. However, the majority of these studies have been carried out in mammalian hosts, which differ in their physiological traits from other taxa. For example, birds possess several unique life history traits, such as hatching from eggs, which may alter the interactions with and transmission of intestinal microbes compared to most mammals. This review covers the diversity of microbial taxa hosted by birds. It also discusses how avian microbial communities strongly influence nutrition, immune function, and processing of toxins in avian hosts, in manners similar to and different from mammalian systems. Finally, areas demanding further research are identified, along with descriptions of existing techniques that could be employed to answer these questions.