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Human tick-borne relapsing fever caused by Borrelia persica is common in western Asia. A survey of 301 horses in Israel revealed 9.96% seropositivity toward B. persica antigens; 1 horse (0.33%) was also PCR positive for B. persica DNA. Phylogenetic analysis supported a transmission cycle involving ticks, humans, and horses.

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.

Tick borne relapsing fever (TBRF) is a zoonosis caused by various Borrelia species transmitted to humans by both soft-bodied and (more recently recognized) hard-bodied ticks. In recent years, molecular diagnostic techniques have allowed to extend our knowledge on the global epidemiological picture of this neglected disease. Nevertheless, due to the patchy occurrence of the disease and the lack of large clinical studies, the knowledge on several clinical aspects of the disease remains limited. In order to shed light on some of these aspects, we have systematically reviewed the literature on TBRF and summarized the existing data on epidemiology and clinical aspects of the disease. Publications were identified by using a predefined search strategy on electronic databases and a subsequent review of the reference lists of the obtained publications. All publications reporting patients with a confirmed diagnosis of TBRF published in English, French, Italian, German, and Hungarian were included. Maps showing the epidemiogeographic mosaic of the different TBRF Borrelia species were compiled and data on clinical aspects of TBRF were analysed. The epidemiogeographic mosaic of TBRF is complex and still continues to evolve. Ticks harbouring TBRF Borrelia have been reported worldwide, with the exception of Antarctica and Australia. Although only molecular diagnostic methods allow for species identification, microscopy remains the diagnostic gold standard in most clinical settings. The most suggestive symptom in TBRF is the eponymous relapsing fever (present in 100% of the cases). Thrombocytopenia is the most suggestive laboratory finding in TBRF. Neurological complications are frequent in TBRF. Treatment is with beta-lactams, tetracyclines or macrolids. The risk of Jarisch-Herxheimer reaction (JHR) appears to be lower in TBRF (19.3%) compared to louse-borne relapsing fever (LBRF) (55.8%). The overall case fatality rate of TBRF (6.5%) and LBRF (4–10.2%) appears to not differ. Unlike LBRF, where perinatal fatalities are primarily attributable to abortion, TBRF-related perinatal fatalities appear to primarily affect newborns.

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.

Relapsing-fever borreliosis caused by Borrelia duttonii is a common cause of complications of pregnancy, miscarriage, and neonatal death in sub-Saharan Africa. We established a murine model of gestational relapsing fever infection for the study of the pathological development of these complications. We demonstrate that B. duttonii infection during pregnancy results in intrauterine growth retardation, as well as placental damage and inflammation, impaired fetal circulation, and decreased maternal hemoglobin levels. We show that spirochetes frequently cross the maternal-fetal barrier, resulting in congenital infection. Furthermore, we compared the severity of infection in pregnant and nonpregnant mice and show that pregnancy has a protective effect. This model closely parallels the consequences of human gestational infection, and our results provide insight into the mechanisms behind the complications of pregnancy that have been reported in human relapsing-fever infection

Relapsing fever is the most frequent bacterial disease in Africa. Four main vector / pathogen complexes are classically recognized, with the louse Pediculus humanus acting as vector for B. recurrentis and the soft ticks Ornithodoros sonrai, O. erraticus and O. moubata acting as vectors for Borrelia crocidurae, B. hispanica and B. duttonii, respectively. Our aim was to investigate the epidemiology of the disease in West, North and Central Africa. From 2002 to 2012, we conducted field surveys in 17 African countries and in Spain. We investigated the occurrence of Ornithodoros ticks in rodent burrows in 282 study sites. We collected 1,629 small mammals that may act as reservoir for Borrelia infections. Using molecular methods we studied genetic diversity among Ornithodoros ticks and Borrelia infections in ticks and small mammals. Of 9,870 burrows investigated, 1,196 (12.1%) were inhabited by Ornithodoros ticks. In West Africa, the southern and eastern limits of the vectors and Borrelia infections in ticks and small mammals were 13°N and 01°E, respectively. Molecular studies revealed the occurrence of nine different Ornithodoros species, including five species new for science, with six of them harboring Borrelia infections. Only B. crocidurae was found in West Africa and three Borrelia species were identified in North Africa: B. crocidurae, B. hispanica, and B. merionesi. Borrelia Spirochetes responsible for relapsing fever in humans are highly prevalent both in Ornithodoros ticks and small mammals in North and West Africa but Ornithodoros ticks seem absent south of 13°N and small mammals are not infected in these regions. The number of Ornithodoros species acting as vector of relapsing fever is much higher than previously known.

Borrelia miyamotoi is a hard tick-borne spirochete genetically related to relapsing fever Borrelia and the etiological agent of an emerging infectious disease in humans. Like relapsing fever Borrelia , B. miyamotoi carries clusters of gene cassettes encoding variable major proteins (Vmps) on multiple linear plasmids and shows antigenic variation in mammalian hosts by switching the expression vmp gene cassette. However, it remains unknown how the switch occurs in B. miyamotoi . Here we determined the whole genome sequences of Japanese B. miyamotoi strains to identify the repertoire and arrangement of vmp gene cassettes on five linear plasmids, and based on this information, analyzed B. miyamotoi clones reisolated from experimentally infected mice. Our analyses revealed that the switch occurred by replacing the expression cassette and its downstream silent cassettes with the long segment from archival plasmid. As the result of this long segment conversion, the first cassette became the expression cassette. Notably, this phenomenon was not due to single gene conversion but the replacement of a long (up to 16 kb or more) plasmid segment. We also show that while bacterial elimination depended on the presence of specific antibodies, the segment conversion was detected at five days post-infection, earlier than antibody production in mice, and even in severe combined immunodeficient mice. These results provide novel insights into the mechanisms that Borrelia evolved to survive and persist in mammalian hosts.

Tick-borne relapsing fever is a neglected and overlooked disease. In Mexico, numerous historical reports document the distribution of Ornithodoros turicata , the vector of Borrelia turicatae , as well as human cases of infection. However, the enzootic cycle and reservoir hosts in Mexico remain unknown. Here, to detect previous infections with relapsing fever Borreliae in wild fauna a retrospective serological analysis was conducted with serum samples collected from raccoons trapped from 2022 to 2025 in the Navachiste region of Sinaloa, Mexico. Using a species-specific antigen, BipA from B. turicatae , and bacterial lysates of this spirochete, we found high exposure among this cohort (30/36 sera, 83.3%). These results indicate the role of raccoon in this area as frequent host of B. turicatae and, together with previous findings, suggest a possible endemic focus of tick-borne relapsing fever in northern Mexico. Our findings remark the need for further investigation into the ecoepidemiology of B. turicatae in this region.

In the southwestern United States, the occurrence and potential for disease spread of Tick-Borne Relapsing Fever (TBRF) has been studied. In Florida, Borrelia pathogens that cause TBRF have only been found in two domestic dogs ( Canis lupus familiaris ), yet the soft tick vector, Ornithodoros turicata americanus , is commonly found throughout the state. The goal of our study was to provide the first large-scale investigation of this disease system in the southeastern US. Our objectives were to: 1) describe the occurrence and prevalence of Borrelia spp. in ticks found throughout their distribution; and 2) phylogenetically describe the pathogen species compared to other isolates of B. turicatae . We pooled ticks by sample location and extracted DNA from over 3,000 ticks systematically collected throughout Florida. Conventional PCR was used with a genus-wide IGS primer to detect any Borrelia spp. present in the ticks. We discovered a low but detectable prevalence (7/745; 0.94%) of the pathogen within localized foci, which could present an epidemiological risk to humans and companion animals in those areas. We Sanger sequenced the 7 pools that were positive for Borrelia spp. and created a phylogenetic tree with our samples and 27 previously described isolates. Our tree showed clustering of our samples into two distinct clades, one that fit with Texas isolates and one that was entirely distinct. We hypothesized that a combination of biogeographic and host influences may be the driving force behind the history of Borrelia turicatae in Florida. Future research is needed to improve our understanding of the drivers of pathogen occurrence and the phylogeography of this species. By understanding the occurrence and phylogenetics of Borrelia turicatae in the state, we can better comprehend and mitigate the risk of this neglected vector-borne disease for humans and companion animals in Florida.

Louse-borne relapsing fever (LBRF) is known to have killed millions of people over the course of European history and remains a major cause of mortality in parts of the world. Its pathogen, Borrelia recurrentis, shares a common vector with global killers such as typhus and plague and is known for its involvement in devastating historical epidemics such as the Irish potato famine. Here, we describe a European and historical genome of B. recurrentis, recovered from a 15th century skeleton from Oslo. Our distinct European lineage has a discrete genomic makeup, displaying an ancestral oppA-1 gene and gene loss in antigenic variation sites. Our results illustrate the potential of ancient DNA research to elucidate dynamics of reductive evolution in a specialized human pathogen and to uncover aspects of human health usually invisible to the archaeological record.