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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.

Borrelia burgdorferi and Borrelia miyamotoi are tick-vectored zoonotic pathogens maintained in wildlife species. Tick populations are establishing in new areas globally in response to climate change and other factors. New Brunswick is a Canadian maritime province at the advancing front of tick population establishment and has seen increasing numbers of ticks carrying B . burgdorferi , and more recently B . miyamotoi . Further, it is part of a region of Atlantic Canada with wildlife species composition differing from much of continental North America and little information exists as to the presence and frequency of infection of Borrelia spp . in wildlife in this region. We used a citizen science approach to collect a wide range of animals including migratory birds, medium-sized mammals, and small mammals. In total we tested 339 animals representing 20 species for the presence of B . burgdorferi and B . miyamotoi . We have developed new nested PCR primers and a protocol with excellent specificity for detecting both of these Borrelia species, both single and double infections, in tissues and organs of various wildlife species. The positive animals were primarily small non-migratory mammals, approximately twice as many were infected with B . burgdorferi than B . miyamotoi and one animal was found infected with both. In addition to established reservoir species, the jumping mouse ( Napaeozapus insignis ) was found frequently infected; this species had the highest infection prevalence for both B . burgdorferi and B . miyamotoi and has not previously been identified as an important carrier for either Borrelia species. Comprehensive testing of tissues found that all instances of B . burgdorferi infection were limited to one tissue within the host, whereas two of the five B . miyamotoi infections were diffuse and found in multiple systems. In the one coinfected specimen, two fetuses were also recovered and found infected with B . miyamotoi . This presumptive transplacental transmission suggests that vertical transmission in mammals is possible. This finding implies that B . miyamotoi could rapidly spread into wildlife populations, as well as having potential human health implications.

Background Ixodes inopinatus was described from Spain on the basis of morphology and partial sequencing of 16S ribosomal DNA. However, several studies suggested that morphological differences between I. inopinatus and Ixodes ricinus are minimal and that 16S rDNA lacks the power to distinguish the two species. Furthermore, nuclear and mitochondrial markers indicated evidence of hybridization between I. inopinatus and I. ricinus . In this study, we tested our hypothesis on tick dispersal from North Africa to Southern Europe and determined the prevalence of selected tick-borne pathogens (TBPs) in I. inopinatus , I. ricinus , and their hybrids. Methods Ticks were collected in Italy and Algeria by flagging, identified by sequencing of partial TROSPA and COI genes, and screened for Borrelia burgdorferi s.l., B. miyamotoi , Rickettsia spp. , and Anaplasma phagocytophilum by polymerase chain reaction and sequencing of specific markers. Results Out of the 380 ticks, in Italy, 92 were I. ricinus , 3 were I. inopinatus , and 136 were hybrids of the two species. All 149 ticks from Algeria were I. inopinatus . Overall, 60% of ticks were positive for at least one TBP. Borrelia burgdorferi s.l. was detected in 19.5% of ticks, and it was significantly more prevalent in Ixodes ticks from Algeria than in ticks from Italy. Prevalence of Rickettsia spotted fever group (SFG) was 51.1%, with significantly greater prevalence in ticks from Algeria than in ticks from Italy. Borrelia miyamotoi and A. phagocytophilum were detected in low prevalence (0.9% and 5.2%, respectively) and only in ticks from Italy. Conclusions This study indicates that I. inopinatus is a dominant species in Algeria, while I. ricinus and hybrids were common in Italy. The higher prevalence of B. burgdorferi s.l. and Rickettsia SFG in I. inopinatus compared with that in I. ricinus might be due to geographical and ecological differences between these two tick species. The role of I. inopinatus in the epidemiology of TBPs needs further investigation in the Mediterranean Basin. Graphical Abstract

Tick-transmitted Borrelia fall into 2 heterogeneous bacterial complexes comprised of multiple species, the relapsing fever (RF) group and the Borrelia burgdorferi sensu lato group, which are the causative agents of Lyme borreliosis (LB), the most common tickborne disease in the Northern Hemisphere. Geographic expansion of LB in the United States and discovery of emerging Borrelia pathogens underscores the importance of surveillance for disease-causing Borrelia. De-identified clinical specimens, submitted by providers throughout the United States, for patients suspected of LB, anaplasmosis, ehrlichiosis, or babesiosis were screened using a Borrelia genus-level TaqMan polymerase chain reaction (PCR). Borrelia species and sequence types (STs) were characterized by multilocus sequence typing (MLST) utilizing next-generation sequencing. Among 7292 specimens tested, 5 Borrelia species were identified: 2 causing LB, B. burgdorferi (n = 25) and B. mayonii (n = 9), and 3 RF borreliae, B. hermsii (n = 1), B. miyamotoi (n = 8), and Candidatus B. johnsonii (n = 1), a species previously detected only in the bat tick, Carios kelleyi. ST diversity was greatest for B. burgdorferi-positive specimens, with new STs identified primarily among synovial fluids. These results demonstrate that broad PCR screening followed by MLST is a powerful surveillance tool for uncovering the spectrum of disease-causing Borrelia species, understanding their geographic distribution, and investigating the correlation between B. burgdorferi STs and joint involvement. Detection of Candidatus B. johnsonii in a patient with suspected tickborne disease suggests this species may be a previously undetected cause of illness in humans exposed to bat ticks.

Background The incidence of Lyme borreliosis varies over time and space through as yet incompletely understood mechanisms. In Europe, Lyme borreliosis is caused by infection with a Borrelia burgdorferi ( s.l. ) genospecies, which is primarily transmitted by a bite of Ixodes ricinus nymphs. The aim of this study was to investigate the spatial and temporal variation in nymphal infection prevalence of B. burgdorferi ( s.l. ) (NIP), density of questing nymphs (DON) and the resulting density of infected nymphs (DIN). Methods We investigated the infection rates in I. ricinus nymphs that were collected monthly between 2009 and 2016 in 12 locations in the Netherlands. Using generalized linear mixed models, we explored how the NIP, DON and DIN varied during the seasons, between years and between locations. We also determined the genospecies of the Borrelia infections and investigated whether the genospecies composition differed between locations. Results The overall NIP was 14.7%. A seasonal pattern in infection prevalence was observed, with higher estimated prevalences in the summer than in the spring and autumn. This, combined with higher nymphal densities in summer, resulted in a pronounced summer peak in the estimated DIN. Over the 7.5-year study period, a significant decrease in infection prevalence was found, as well as a significant increase in nymphal density. These two effects appear to cancel each other out; the density of infected nymphs, which is the product of NIP × DON, showed no significant trend over years. Mean infection prevalence (NIP, averaged over all years and all months) varied considerably between locations, ranging from 5 to 26%. Borrelia genospecies composition differed between locations: in some locations almost all infections consisted of B. afzelii , whereas other locations had more diverse genospecies compositions. Conclusion In the Netherlands, the summer peak in DIN is a result of peaks in both NIP and DON. No significant trend in DIN was observed over the years of the study, and variations in DIN between locations were mostly a result of the variation in DON. There were considerable differences in acarological risk between areas in terms of infection prevalence and densities of ticks as well as in Borrelia genospecies composition. Graphical Abstract

Tick-borne relapsing fever caused by the spirochaete Borrelia duttonii is a common cause of serious illness in central Tanzania. Screening of Ornithodoros sp ticks from infested houses for the presence of B duttonii had detected a previously unidentified species of Borrelia. We investigated whether this species infected the human population in a central Tanzanian village, by use of blood slide examination and PCR. PCR was twice as sensitive in detection of infections, showing Borrelia sp in six (11%) of 54 children with fever, and in 13 (4%) of 307 otherwise healthy children. Genotyping Borrelia from 17 infections identified Borrelia duttonii and an unnamed species. Our findings show that the newly discovered species is a causal agent of tick-borne relapsing fever.

The genus Borrelia, originally described by Swellengrebel in 1907, contains tick- or louse-transmitted spirochetes belonging to the relapsing fever (RF) group of spirochetes, the Lyme borreliosis (LB) group of spirochetes and spirochetes that form intermittent clades. In 2014 it was proposed that the genus Borrelia should be separated into two genera; Borrelia Swellengrebel 1907 emend. Adeolu and Gupta 2014 containing RF spirochetes and Borreliella Adeolu and Gupta 2014 containing LB group of spirochetes. In this study we conducted an analysis based on a method that is suitable for bacterial genus demarcation, the percentage of conserved proteins (POCP). We included RF group species, LB group species and two species belonging to intermittent clades, Borrelia turcica Güner et al. 2004 and Candidatus Borrelia tachyglossi Loh et al. 2017. These analyses convincingly showed that all groups of spirochetes belong into one genus and we propose to emend, and re-unite all groups in, the genus Borrelia.

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 × 10 0 to 7.0 × 10 5 . 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. Graphical Abstract

We obtained 5 isolates of Borrelia turicatae from ticks captured in a public park in Aguascalientes, Mexico. A serologic survey in resident fauna showed antibodies against B. turicatae. Relapsing fever borrelias are present in Ornithodoros turicata ticks and circulate in a zoonotic cycle, posing a risk for human infection.