Detection of Borrelia burgdorferi sensu stricto ospC alleles associated with human lyme borreliosis worldwide in non-human-biting tick Ixodes affinis and rodent hosts in Southeastern United States

Natural selection and recombination at host-interacting lipoprotein loci drive genome diversification of Lyme disease and related bacteria

Lyme disease, caused by spirochetes in the Borrelia burgdorferi sensu lato clade within the Borrelia genus, is transmitted by Ixodes ticks and is currently the most prevalent and rapidly expanding tick-borne disease in Europe and North America. We report complete genome sequences of 47 isolates that encompass all established species in this clade while highlighting the diversity of the widespread human pathogenic species B. burgdorferi. A similar set of plasmids has been maintained throughout Borrelia divergence, indicating that they are a key adaptive feature of this genus. Phylogenetic reconstruction of all sequenced Borrelia genomes revealed the original divergence of Eurasian and North American lineages and subsequent dispersals that introduced B. garinii, B. bavariensis, B. lusitaniae, B. valaisiana, and B. afzelii from East Asia to Europe and B. burgdorferi and B. finlandensis from North America to Europe. Molecular phylogenies of the universally present core replicons (chromosome and cp26 and lp54 plasmids) are highly consistent, revealing a strong clonal structure. Nonetheless, numerous inconsistencies between the genome and gene phylogenies indicate species dispersal, genetic exchanges, and rapid sequence evolution at plasmid-borne loci, including key host-interacting lipoprotein genes. While localized recombination occurs uniformly on the main chromosome at a rate comparable to mutation, lipoprotein-encoding loci are recombination hotspots on the plasmids, suggesting adaptive maintenance of recombinant alleles at loci directly interacting with the host. We conclude that within- and between-species recombination facilitates adaptive sequence evolution of host-interacting lipoprotein loci and contributes to human virulence despite a genome-wide clonal structure of its natural populations.

IMPORTANCE

Lyme disease (also called Lyme borreliosis in Europe), a condition caused by spirochete bacteria of the genus Borrelia, transmitted by hard-bodied Ixodes ticks, is currently the most prevalent and rapidly expanding tick-borne disease in the United States and Europe. Borrelia interspecies and intraspecies genome comparisons of Lyme disease-related bacteria are essential to reconstruct their evolutionary origins, track epidemiological spread, identify molecular mechanisms of human pathogenicity, and design molecular and ecological approaches to disease prevention, diagnosis, and treatment. These Lyme disease-associated bacteria harbor complex genomes that encode many genes that do not have homologs in other organisms and are distributed across multiple linear and circular plasmids. The functional significance of most of the plasmid-borne genes and the multipartite genome organization itself remains unknown. Here we sequenced, assembled, and analyzed whole genomes of 47 Borrelia isolates from around the world, including multiple isolates of the human pathogenic species. Our analysis elucidates the evolutionary origins, historical migration, and sources of genomic variability of these clinically important pathogens. We have developed web-based software tools (BorreliaBase.org) to facilitate dissemination and continued comparative analysis of Borrelia genomes to identify determinants of human pathogenicity.

Monthly fluctuation of parasitism by adult Ixodes keiransi ticks in dogs from Yucatán, Mexico

The monthly fluctuation of adult Ixodes keiransi in dogs from two cattle farms in southeastern Mexico was determined. In ranch 1 (R1), 6-7 mixed breed dogs from six months to five years of age; while in ranch 2 (R2), 7-8 mixed breed dogs from one to four years of age, were followed. All dogs were monthly inspected for tick infestation through one year. The abundance of dogs infested with ticks was estimated for each month. Tick specimens were taxonomically identified as I. keiransi using morphological features. In R1 the dogs were inspected 60 times and in R2 90 times. The overall proportion of dogs infested by ticks through the year was 75% (60/80) in R1 and 67% (67/90) in R2. The higher abundance of adult I. keiransi parasitizing dogs was from July to December with maximum peaks from September to November. In April, May and June, no ticks were observed on dogs from both ranches. Tick abundance fluctuation showed a concordant pattern with rainfall but with a delay because de maximum peak of I. keiransi abundance was almost two months after the greatest rainfall peak. It is concluded that, in some conditions, the adult I. keiransi in southeastern Mexico presents high-infested rates on dogs and a maximum abundance from September to November. The I. keiransi abundance fluctuation showed a concordant pattern with rainfall.

Diversity and host specificity of Borrelia burgdorferi's outer surface protein C (ospC) alleles in synanthropic mammals, with a notable ospC allele U absence from mixed infections

Interactions among pathogen genotypes that vary in host specificity may affect overall transmission dynamics in multi-host systems. Borrelia burgdorferi, a bacterium that causes Lyme disease, is typically transmitted among wildlife by Ixodes ticks. Despite the existence of many alleles of B. burgdorferi's sensu stricto outer surface protein C (ospC) gene, most human infections are caused by a small number of ospC alleles ["human infectious alleles" (HIAs)], suggesting variation in host specificity associated with ospC. To characterize the wildlife host association of B. burgdorferi's ospC alleles, we used metagenomics to sequence ospC alleles from 68 infected individuals belonging to eight mammalian species trapped at three sites in suburban New Brunswick, New Jersey (USA). We found that multiple allele ("mixed") infections were common. HIAs were most common in mice (Peromyscus spp.) and only one HIA was detected at a site where mice were rarely captured. ospC allele U was exclusively found in chipmunks (Tamias striatus), and although a significant number of different alleles were observed in chipmunks, including HIAs, allele U never co-occurred with other alleles in mixed infections. Our results suggest that allele U may be excluding other alleles, thereby reducing the capacity of chipmunks to act as reservoirs for HIAs.

Pathogenicity and virulence of Borrelia burgdorferi

Infection with Borrelia burgdorferi often triggers pathophysiologic perturbations that are further augmented by the inflammatory responses of the host, resulting in the severe clinical conditions of Lyme disease. While our apprehension of the spatial and temporal integration of the virulence determinants during the enzootic cycle of B. burgdorferi is constantly being improved, there is still much to be discovered. Many of the novel virulence strategies discussed in this review are undetermined. Lyme disease spirochaetes must surmount numerous molecular and mechanical obstacles in order to establish a disseminated infection in a vertebrate host. These barriers include borrelial relocation from the midgut of the feeding tick to its body cavity and further to the salivary glands, deposition to the skin, haematogenous dissemination, extravasation from blood circulation system, evasion of the host immune responses, localization to protective niches, and establishment of local as well as distal infection in multiple tissues and organs. Here, the various well-defined but also possible novel strategies and virulence mechanisms used by B. burgdorferi to evade obstacles laid out by the tick vector and usually the mammalian host during colonization and infection are reviewed.

Concurrent Infection of the Human Brain with Multiple Borrelia Species

Lyme disease (LD) spirochetes are well known to be able to disseminate into the tissues of infected hosts, including humans. The diverse strategies used by spirochetes to avoid the host immune system and persist in the host include active immune suppression, induction of immune tolerance, phase and antigenic variation, intracellular seclusion, changing of morphological and physiological state in varying environments, formation of biofilms and persistent forms, and, importantly, incursion into immune-privileged sites such as the brain. Invasion of immune-privileged sites allows the spirochetes to not only escape from the host immune system but can also reduce the efficacy of antibiotic therapy. Here we present a case of the detection of spirochetal DNA in multiple loci in a LD patient's post-mortem brain. The presence of co-infection with Borrelia burgdorferi sensu stricto and Borrelia garinii in this LD patient's brain was confirmed by PCR. Even though both spirochete species were simultaneously present in human brain tissue, the brain regions where the two species were detected were different and non-overlapping. The presence of atypical spirochete morphology was noted by immunohistochemistry of the brain samples. Atypical morphology was also found in the tissues of experimentally infected mice, which were used as a control.

Prevalence of Borrelia burgdorferi and diversity of its outer surface protein C (ospC) alleles in blacklegged ticks (Ixodes scapularis) in Delaware

Characterizing the diversity of genes associated with virulence and transmission of a pathogen across the pathogen's distribution can inform our understanding of host infection risk. Borrelia burgdorferi is a vector-borne bacterium that causes Lyme disease in humans and is common in the United States. The outer surface protein C (ospC) gene of B. burgdorferi exhibits substantial genetic variation across the pathogen's distribution and plays a critical role in virulence and transmission in vertebrate hosts. In fact, B. burgdorferi infections that disseminate across host tissues in humans are associated with only a subset of ospC alleles. Delaware has a high incidence of Lyme disease, but the diversity of ospC in B. burgdorferi in the state has not been evaluated. We used PCR to amplify ospC in B. burgdorferi-infected blacklegged ticks (Ixodes scapularis) in sites statewide and used short-read sequencing to identify ospC alleles. B. burgdorferi prevalence in blacklegged ticks varied across sites, but not significantly so. We identified 15 previously characterized ospC alleles accounting for nearly all of the expected diversity of alleles across the sites as estimated using the Chao1 index. Nearly 40% of sequenced infections (23/58) had more than one ospC allele present suggesting mixed strain infections and the relative frequencies of alleles in single infections were positively correlated with their relative frequencies in mixed infections. Turnover of ospC alleles was positively related to distance between sites with closer sites having more similar allele compositions than more distant sites. This suggests a degree of B. burgdorferi dispersal limitation or habitat specialization. OspC alleles known to cause disseminated infections in humans were found at the highest frequencies across sites, corresponding to Delaware's high incidence of Lyme disease.

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.

Sexual Transmission of Lyme Borreliosis? The Question That Calls for an Answer

Transmission of the causative agents of numerous infectious diseases might be potentially conducted by various routes if this is supported by the genetics of the pathogen. Various transmission modes occur in related pathogens, reflecting a complex process that is specific for each particular host-pathogen system that relies on and is affected by pathogen and host genetics and ecology, ensuring the epidemiological spread of the pathogen. The recent dramatic rise in diagnosed cases of Lyme borreliosis might be due to several factors: the shifting of the distributional range of tick vectors caused by climate change; dispersal of infected ticks due to host animal migration; recent urbanization; an increasing overlap of humans' habitat with wildlife reservoirs and the environment of tick vectors of Borrelia; improvements in disease diagnosis; or establishment of adequate surveillance. The involvement of other bloodsucking arthropod vectors and/or other routes of transmission (human-to-human) of the causative agent of Lyme borreliosis, the spirochetes from the Borrelia burgdorferi sensu lato complex, has been speculated to be contributing to increased disease burden. It does not matter how controversial the idea of vector-free spirochete transmission might seem in the beginning. As long as evidence of sexual transmission of Borrelia burgdorferi both between vertebrate hosts and between tick vectors exists, this question must be addressed. In order to confirm or refute the existence of this phenomenon, which could have important implications for Lyme borreliosis epidemiology, the need of extensive research is obvious and required.

Borrelia genospecies in Ixodes sp. cf. Ixodes affinis (Acari: Ixodidae) from Argentina

The aim of this work was to evaluate the presence of Borrelia infection in Ixodes sp. cf. Ixodes affinis ticks from Argentina. Specimens of Ixodes sp. cf. I. affinis were collected on vegetation and birds in five locations belonging the most humid part of the Chaco Biogeographic Province. Specimens were tested for Borrelia infection by nested-PCR targeting the flaB gene and the rrfA-rrlB intergenic spacer region (IGS), sequenced and phylogenetically analyzed. A total of 48 Ixodes sp. cf. I. affinis (12 questing adults from vegetation and 20 nymphs and 16 larvae on nine bird species: Arremon flavirostris, Basileuterus culicivorus, Campylorhamphus trochilirostris, Myiothlypis leucoblephara, Tachyphonus rufus, Thlypopsis sordida, Turdus amaurochalinus, Turdus rufiventris and Troglodytes aedon) were collected. Twelve adults, 14 nymphs and 11 larvae (3 individually and 8 in 3 pools) were analyzed. Partial sequences were detected in 6 adults, 11 nymphs and 4 larvae (2 individual and 2 pools). Phylogenetically, the Borrelia found in Ixodes sp. cf. I. affinis belongs to the B. burgdorferi sensu lato (s. l.) complex. The partial sequences obtained from the borrelian gene flaB and IGS were associated to two groups formed by sequences previously detected in Ixodes fuscipes, Ixodes longiscutatus and Ixodes pararicinus from the Southern Cone of America in northern Argentina, southern Brazil and Uruguay. The results of this work suggest that the haplotypes of B. burgdorferi s. l. complex detected in the three species of the I. ricinus complex distributed in the Southern Cone of America are related and widely distributed.

Regional prevalences of Borrelia burgdorferi, Borrelia bissettiae, and Bartonella henselae in Ixodes affinis, Ixodes pacificus and Ixodes scapularis in the USA

The objective of this work was to determine the prevalence of Borrelia and Bartonella species in Ixodes spp. ticks collected from 16 USA states. Genus PCR amplification and sequence analysis of Bartonella and Borrelia 16SsRNA-23SsRNA intergenic regions were performed on DNA extracted from 929 questing adult ticks (671 Ixodes scapularis, 155 Ixodes affinis, and 103 Ixodes pacificus). Overall, 129/929 (13.9%) Ixodes ticks were PCR positive for Borrelia burgdorferi sensu stricto, 48/929 for B. bissettiae whereas 23/929 (2.5%) were PCR positive for a Bartonella henselae. Borrelia bissettiae or B. burgdorferi s.s. and B. henselae co-infections were found in I. affinis from North Carolina at a rate of 4.5%; in a single I. scapularis from Minnesota, but not in I. pacificus. For both bacterial genera, PCR positive rates were highly variable depending on geographic location and tick species, with Ixodes affinis (n = 155) collected from North Carolina, being the tick species with the highest prevalence's for both Borrelia spp. (63.2%) and B. henselae (10.3%). Based on the results of this and other published studies, improved understanding of the enzootic cycle, transmission dynamics, and vector competence of Ixodes species (especially I. affinis) for transmission of Borrelia spp. and B. henselae should be a public health research priority.

Epitope mapping of Borrelia burgdorferi OspC protein in homodimeric fold

In current work, we used recombinant OspC protein derived from B. afzelii strain BRZ31 in the native homodimeric fold for mice immunization and following selection process to produce three mouse monoclonal antibodies able to bind to variable parts of up to five different OspC proteins. Applying the combination of mass spectrometry assisted epitope mapping and affinity based theoretical prediction we have localized regions responsible for antigen-antibody interactions and approximate epitopes' amino acid composition. Two mAbs (3F4 and 2A9) binds to linear epitopes located in previously described immunogenic regions in the exposed part of OspC protein. The third mAb (2D1) recognises highly conserved discontinuous epitope close to the ligand binding domain 1.

Differences in Genotype, Clinical Features, and Inflammatory Potential of Borrelia burgdorferi sensu stricto Strains from Europe and the United States

Strains from the United States are more virulent and have greater inflammatory potential.

Borrelia burgdorferi sensu stricto isolates from patients with erythema migrans in Europe and the United States were compared by genotype, clinical features of infection, and inflammatory potential. Analysis of outer surface protein C and multilocus sequence typing showed that strains from these 2 regions represent distinct genotypes. Clinical features of infection with B. burgdorferi in Slovenia were similar to infection with B. afzelii or B. garinii, the other 2 Borrelia spp. that cause disease in Europe, whereas B. burgdorferi strains from the United States were associated with more severe disease. Moreover, B. burgdorferi strains from the United States induced peripheral blood mononuclear cells to secrete higher levels of cytokines and chemokines associated with innate and Th1-adaptive immune responses, whereas strains from Europe induced greater Th17-associated responses. Thus, strains of the same B. burgdorferi species from Europe and the United States represent distinct clonal lineages that vary in virulence and inflammatory potential.

Progress in the molecular diagnosis of Lyme disease

INTRODUCTION

Current laboratory testing of Lyme borreliosis mostly relies on serological methods with known limitations. Diagnostic modalities enabling direct detection of pathogen at the onset of the clinical signs could overcome some of the limitations. Molecular methods detecting borrelial DNA seem to be the ideal solution, although there are some aspects that need to be considered. Areas covered: This review represent summary and discussion of the published data obtained from literature searches from PubMed and The National Library of Medicine (USA) together with our own experience on molecular diagnosis of Lyme disease. Expert commentary: Molecular methods are promising and currently serve as supporting diagnostic testing in Lyme borreliosis. Since the field of molecular diagnostics is under rapid development, molecular testing could become an important diagnostic modality.

Sensitivity of Lyme Borreliosis Spirochetes to Serum Complement of Regular Zoo Animals: Potential Reservoir Competence of Some Exotic Vertebrates

Reaction of vertebrate serum complement with different Borrelia burgdorferi sensu lato species is used as a basis in determining reservoir hosts among domesticated and wild animals. Borrelia burgdorferi sensu stricto, Borrelia garinii, and Borrelia afzelii were tested for their sensitivity to sera of exotic vertebrate species housed in five zoos located in the Czech Republic. We confirmed that different Borrelia species have different sensitivity to host serum. We found that tolerance to Borrelia infection possessed by hosts might differ among individuals of the same genera or species and is not affected by host age or sex. Of all zoo animals included in our study, carnivores demonstrated the highest apparent reservoir competency for Lyme borreliosis spirochetes. We showed that selected exotic ungulate species are tolerant to Borrelia infection. For the first time we showed the high tolerance of Siamese crocodile to Borrelia as compared to the other studied reptile species. While exotic vertebrates present a limited risk to the European human population as reservoirs for the causative agents of Lyme borreliosis, cases of incidental spillover infection could lead to successful replication of the pathogens in a new host, changing the status of selected exotic species and their role in pathogen emergence or maintenance. The question if being tolerant to pathogen means to be a competent reservoir host still needs an answer, simply because the majority of exotic animals might never be exposed to spirochetes in their natural environment.

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

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

DNA-based identification and OspC serotyping in cultures of Borrelia burgdorferi s.l. isolated from ticks collected in the Moravia (Czech Republic)

Two different genetic loci, flaB and ospC, were employed to assign genospecies and OspC phylogenetic type to 18 strains isolated from ticks collected in Pisárky, a suburban park in the city of Brno, Czech Republic. The RFLP analysis revealed three different genospecies (B. afzelii, B. garinii, and B. valaisiana). Three samples from the collection contained more than one genospecies. In the other 15 strains, nucleotide sequences of flaB and ospC were determined. The following phylogenetic analysis assigned 12 isolates to genospecies B. garinii and three to B. afzelii. These isolates were further subdivided into seven distinct ospC groups. The most related OspC types were G2, G4, and G5 (B. garinii) and A3 and A8 (B. afzelii).

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>

New Records of Ixodes affinis (Acari: Ixodidae) Parasitizing Avian Hosts in Southeastern Virginia

Ixodes affinis Neumann (Acari: Ixodidae) is a hard-bodied tick species distributed throughout much of the southeastern United States. Although I. affinis does not parasitize humans, it is a competent vector of Borrelia burgdorferi sensu stricto, the causative-agent of Lyme disease, and thus contributes to the enzootic maintenance of this pathogen. This study presents evidence of I. affinis parasitizing five new host passerine species. During 2012-2014, 1,888 birds were captured and examined for ticks, and 18 immature I. affinis were collected from 12 birds-six Carolina Wrens (Thyrothorus ludovicianus); two Brown Thrashers (Toxostoma rufum); and one American Robin (Turdus migratorius), Eastern Towhee (Pipilo erythrophthalmus), Northern Cardinal (Cardinalis cardinalis), and White-throated Sparrow (Zonotrichia albicollis). Of 15 larvae and 3 nymphs collected, one nymph tested positive for B. burgdorferi DNA. I. affinis was found co-feeding on birds with immature Amblyomma americanum (L.), Ixodes brunneus Koch, Ixodes dentatus Marx, Ixodes scapularis Say, and Haemaphysalis leporispalustris Packard. The results of this research provide a better understanding of I. affinis hosts and identify avian taxa that may play a role in the maintenance and dispersal of this tick species.

Isolation of live Borrelia burgdorferi sensu lato spirochaetes from patients with undefined disorders and symptoms not typical for Lyme borreliosis

Lyme borreliosis is a multisystem disorder with a diverse spectrum of clinical manifestations, caused by spirochaetes of the Borrelia burgdorferi sensu lato complex. It is an infectious disease that can be successfully cured by antibiotic therapy in the early stages; however, the possibility of the appearance of persistent signs and symptoms of disease following antibiotic treatment is recognized. It is known that Lyme borreliosis mimics multiple diseases that were never proven to have a spirochaete aetiology. Using complete modified Kelly-Pettenkofer medium we succeeded in cultivating live B. burgdorferi sensu lato spirochaetes from samples taken from people who suffered from undefined disorders, had symptoms not typical for Lyme borreliosis, but who had undergone antibiotic treatment due to a suspicion of having Lyme disease even though they were seronegative. We report the first recovery of live B. burgdorferi sensu stricto from residents of southeastern USA and the first successful cultivation of live Borrelia bissettii-like strain from residents of North America. Our results support the fact that B. bissettii is responsible for human Lyme borreliosis worldwide along with B. burgdorferi s.s. The involvement of new spirochaete species in Lyme borreliosis changes the understanding and recognition of clinical manifestations of this disease.

Invasive potential of Borrelia burgdorferi sensu stricto ospC type L strains increases the possible disease risk to humans in the regions of their distribution

BACKGROUND

Analysis of Borrelia burgdorferi ospC types from the southeastern U.S.A. supported the common belief that various ospC types are geographically restricted and host specific. Being widely distributed in the region, the southeastern population of B. burgdorferi is represented by a surprisingly small number of ospC types. Types B, G and H are dominant or common and are invasive, while scarce type L, restricted mostly to the southeastern U.S.A., is believed to rarely if ever cause human Lyme disease. OspC type B and L strains are represented in the region at the same rate, however their distribution among tick vectors and vertebrate hosts is unequal.

FINDINGS

Direct diagnostics was used to analyze the ability of B. burgdorferi ospC type L strains to disseminate into host tissues. Mice were infected by subcutaneous injections of B. burgdorferi strains of various ospC types with different invasive capability. Spirochete levels were examined in ear, heart, bladder and joint tissues. Noninfected I. ricinus larvae were fed on infected mice until repletion. Infection rates were determined in molted nymphs. Infected nymphs were then fed on naïve mice, and spirochete transmission from infected nymphs to mice was confirmed.

CONCLUSIONS

B. burgdorferi ospC type L strains from the southeastern U.S.A. have comparable potential to disseminate into host tissues as ospC types strains commonly associated with human Lyme disease in endemic European and North American regions. We found no difference in the invasive ability of ospC type B and L strains originated either from tick vectors or vertebrate hosts.

Lyme disease risk not amplified in a species-poor vertebrate community: similar Borrelia burgdorferi tick infection prevalence and OspC genotype frequencies

The effect of biodiversity declines on human health is currently debated, but empirical assessments are lacking. Lyme disease provides a model system to assess relationships between biodiversity and human disease because the etiologic agent, Borrelia burgdorferi, is transmitted in the United States by the generalist black-legged tick (Ixodes scapularis) among a wide range of mammalian and avian hosts. The 'dilution effect' hypothesis predicts that species-poor host communities dominated by white-footed mice (Peromyscus leucopus) will pose the greatest human risk because P. leucopus infects the largest numbers of ticks, resulting in higher human exposure to infected I. scapularis ticks. P. leucopus-dominated communities are also expected to maintain a higher frequency of those B. burgdorferi outer surface protein C (ospC) genotypes that this host species more efficiently transmits ('multiple niche polymorphism' hypothesis). Because some of these genotypes are human invasive, an additive increase in human disease risk is expected in species-poor settings. We assessed these theoretical predictions by comparing I. scapularis nymphal infection prevalence, density of infected nymphs and B. burgdorferi genotype diversity at sites on Block Island, RI, where P. leucopus dominates the mammalian host community, to species-diverse sites in northeastern Connecticut. We found no support for the dilution effect hypothesis; B. burgdorferi nymphal infection prevalence was similar between island and mainland and the density of B. burgdorferi infected nymphs was higher on the mainland, contrary to what is predicted by the dilution effect hypothesis. Evidence for the multiple niche polymorphism hypothesis was mixed: there was lower ospC genotype diversity at island than mainland sites, but no overrepresentation of genotypes with higher fitness in P. leucopus or that are more invasive in humans. We conclude that other mechanisms explain similar nymphal infection prevalence in both communities and that high ospC genotype diversity can be maintained in both species-poor and species-rich communities.

Evolutionary genomics of Borrelia burgdorferi sensu lato: findings, hypotheses, and the rise of hybrids

Borrelia burgdorferi sensu lato (B. burgdorferi s.l.), the group of bacterial species represented by Lyme disease pathogens, has one of the most complex and variable genomic architectures among prokaryotes. Showing frequent recombination within and limited gene flow among geographic populations, the B. burgdorferi s.l. genomes provide an excellent window into the processes of bacterial evolution at both within- and between-population levels. Comparative analyses of B. burgdorferi s.l. genomes revealed a highly dynamic plasmid composition but a conservative gene repertoire. Gene duplication and loss as well as sequence variations at loci encoding surface-localized lipoproteins (e.g., the PF54 genes) are strongly associated with adaptive differences between species. There are a great many conserved intergenic spacer sequences that are candidates for cis-regulatory elements and non-coding RNAs. Recombination among coexisting strains occurs at a rate approximately three times the mutation rate. The coexistence of a large number of genomic groups within local B. burgdorferi s.l. populations may be driven by immune-mediated diversifying selection targeting major antigen loci as well as by adaptation to multiple host species. Questions remain regarding the ecological causes (e.g., climate change, host movements, or new adaptations) of the ongoing range expansion of B. burgdorferi s.l. and on the genomic variations associated with its ecological and clinical variability. Anticipating an explosive growth of the number of B. burgdorferi s.l. genomes sampled from both within and among species, we propose genome-based methods to test adaptive mechanisms and to identify molecular bases of phenotypic variations. Genome sequencing is also necessary for monitoring a likely increase of genetic admixture of previously isolated species and populations in North America and elsewhere.

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

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

Divergence of Borrelia burgdorferi sensu lato spirochetes could be driven by the host: diversity of Borrelia strains isolated from ticks feeding on a single bird

BACKGROUND

The controversy surrounding the potential impact of birds in spirochete transmission dynamics and their capacity to serve as a reservoir has existed for a long time. The majority of analyzed bird species are able to infect larval ticks with Borrelia. Dispersal of infected ticks due to bird migration is a key to the establishment of new foci of Lyme borreliosis. The dynamics of infection in birds supports the mixing of different species, the horizontal exchange of genetic information, and appearance of recombinant genotypes.

METHODS

Four Borrelia burgdorferi sensu lato strains were cultured from Ixodes minor larvae and four strains were isolated from Ixodes minor nymphs collected from a single Carolina Wren (Thryothorus ludovicianus). A multilocus sequence analysis that included 16S rRNA, a 5S-23S intergenic spacer region, a 16S-23S internal transcribed spacer, flagellin, p66, and ospC separated 8 strains into 3 distinct groups. Additional multilocus sequence typing of 8 housekeeping genes, clpA, clpX, nifS, pepX, pyrG, recG, rplB, and uvrA was used to resolve the taxonomic status of bird-associated strains.

RESULTS

Results of analysis of 14 genes confirmed that the level of divergence among strains is significantly higher than what would be expected for strains within a single species. The presence of cross-species recombination was revealed: Borrelia burgdorferi sensu stricto housekeeping gene nifS was incorporated into homologous locus of strain, previously assigned to B. americana.

CONCLUSIONS

Genetically diverse Borrelia strains are often found within the same tick or same vertebrate host, presenting a wide opportunity for genetic exchange. We report the cross-species recombination that led to incorporation of a housekeeping gene from the B. burgdorferi sensu stricto strain into a homologous locus of another bird-associated strain. Our results support the hypothesis that recombination maintains a majority of sequence polymorphism within Borrelia populations because of the re-assortment of pre-existing sequence variants. Even if our findings of broad genetic diversity among 8 strains cultured from ticks that fed on a single bird could be the exception rather than the rule, they support the theory that the diversity and evolution of LB spirochetes is driven mainly by the host.