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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.

Relapsing fever group  Borrelia (RFGB) are motile spirochetes transmitted to mammalian or avian hosts through the bite of hematophagous arthropods, such as soft ticks (Argasidae), hard ticks (Ixodidae) and the human clothing lice. RFGB can infect pets such as dogs and cats, as well as birds, cattle and humans. Borrelia recurrentis , B. anserina and B. theileri are considered to have worldwide distribution, affecting humans, domestic birds and ruminants, respectively. Borrelia spp. associated with soft ticks are transmitted mainly by Ornithodoros ticks and thrive in endemic foci in tropical and subtropical latitudes. Nowadays, human cases of soft tick-borne relapsing fever remain neglected diseases in several countries, and the impact these spirochetes have on the health of wild and domestic animals is largely understudied. Human infection with RFGB is difficult to diagnose, given the lack of distinguishing clinical features (undifferentiated febrile illness). Clinically, soft tick or louse-borne relapsing fever is often confused with other etiologies, such as malaria, typhoid or dengue. In Latin America, during the first half of the twentieth century historical documents elaborated by enlightened physicians were seminal, and resulted in the identification of RFGB and their associated vectors in countries such as Mexico, Panama, Colombia, Venezuela, Peru and Argentina. Almost 80 years later, research on relapsing fever spirochetes is emerging once again in Latin America, with molecular characterizations and isolations of novel RFGB members in Panama, Bolivia, Brazil and Chile. In this review we summarize historical aspects of RFGB in Latin America and provide an update on the current scenario regarding these pathogens in the region. To accomplish this, we conducted an exhaustive search of all the published literature for the region, including old medical theses deposited in libraries of medical academies. RFGB were once common pathogens in Latin America, and although unnoticed for many years, they are currently the focus of interest among the scientific community. A One Health perspective should be adopted to tackle the diseases caused by RFGB, since these spirochetes have never disappeared and the maladies they cause may be confused with etiologies with similar symptoms that prevail in the region. Graphical Abstract

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.

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.

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.

Background Relapsing fever borreliosis is an infectious disease caused by bacteria of the genus  Borrelia, inflicting recurrent episodes of fever and spirochetemia in humans. Borrelia persica, the causative agent of relapsing fever in Israel, is prevalent over a broad geographic area that extends from India to Egypt. It is transmitted by the soft tick  Ornithodoros tholozani and causes disease in humans as well as domestic cats and dogs. The goal of this study was to survey domestic dogs and cats in Israel for infection with B. persica . Methods Blood, sera and demographic and clinical data were collected from dogs and cats brought for veterinary care in central Israel. PCR followed by DNA sequencing was used to detect B. persica DNA in blood samples, and an enzyme-linked immunosorbent assay (ELISA) was used to detect antibodies reactive with B. persica antigens in sera from the same animals. This is the first serological survey of B. persica in dogs and the first survey for antibodies reactive with a relapsing fever Borrelia sp. in cats globally. Results Four of the 208 dogs (1.9%) and three of 103 cats (2.9%) sampled were positive by PCR for B. persica DNA, and 24 dogs (11.5%) and 18 cats (17.5%) were seropositive for B. persica antigen by ELISA. The ratio between PCR-positivity and seropositivity in both the dog and cat populations was 1:6. All four PCR-positive dogs and two of three PCR-positive cats were seronegative, suggesting a probable recent infection. Thrombocytopenia showed significant association with seropositivity in dogs ( P  = 0.003). In cats, anemia had a significant association with seropositivity ( P  = 0.0001), and thrombocytopenia was associated with the combined prevalence of seropositivity or PCR-positivity ( P  = 0.022). Conclusions Borrelia persica infection is more prevalent and widespread in domestic canine and feline populations in Israel than previously thought. Dogs and cats may play a role as reservoirs and sentinels for human infection. Precautions should be taken to prevent transfusion-transmitted infection between blood donor and recipient animals. Graphic Abstract

Background Relapsing fever (RF) is an acute infectious disease caused by arthropod-borne spirochetes of the genus Borrelia . The disease is characterized by recurrent episodes of fever that concur with spirochetemia. The RF borrelioses include louse-borne RF caused by Borrelia recurrentis and tick-borne endemic RF transmitted by argasid soft ticks and caused by several Borrelia spp. such as B. crocidurae , B. coriaceae , B. duttoni , B. hermsii , B. hispanica and B. persica . Human infection with B. persica is transmitted by the soft tick Ornithodoros tholozani and has been reported from Iran, Israel, Egypt, India, and Central Asia. Methods During 2003–2015, five cats and five dogs from northern, central and southern Israel were presented for veterinary care and detected with borrelia spirochetemia by blood smear microscopy. The causative infective agent in these animals was identified and characterized by PCR from blood and sequencing of parts of the flagellin ( flab ), 16S rRNA and glycerophosphodiester phosphodiestrase ( GlpQ ) genes. Results All animals were infected with B. persica genetically identical to the causative agent of human RF. Phylogenetic analysis indicated that DNA sequences from these pet carnivores clustered together with B. persica genotypes I and II from humans and O. tholozani ticks and distinctly from other RF Borrelia spp. The main clinical findings in cats included lethargy, anorexia, anemia in 5/5 cats and thrombocytopenia in 4/5. All dogs were lethargic and anorectic, 4/5 were febrile and anemic and 3/5 were thrombocytopenic. Three dogs were co-infected with Babesia spp. The animals were all treated with antibiotics and the survival rate of both dogs and cats was 80 %. The cat and dog that succumbed to disease died one day after the initiation of antibiotic treatment, while survival in the others was followed by the rapid disappearance of spirochetemia. Conclusions This is the first report of disease due to B. persica infection in cats and the first case series in dogs. Infection was associated with anemia and thrombocytopenia. Fever was more frequently observed in dogs than cats. Domestic canines and felines suffer from clinical disease due to B. persica infection and may also serve as sentinels for human infection.

Tick-borne relapsing fever (TBRF) is the most common vector-borne bacterial disease in humans in West Africa. It is frequently clinically confused with malaria. Our study aims to determine, on a micro-geographic scale, the conditions for the maintenance and spread of TBRF in the Niakhar district of Senegal. We conducted clinical, entomological and animal reservoir investigations. Field surveys were carried out in order to investigate the presence of Ornithodoros sonrai vector ticks and to detect Borrelia spp. by qPCR using the 16S rRNA and glpQ genes, respectively. Micromammal trapping series were carried out inside homes and Borrelia infection was detected using brain tissue qPCR. Capillary blood samples from febrile patients were also tested for Borrelia using qPCR. More than 97% (40/41) of the villages surveyed were infested with O. sonrai ticks. The prevalence of Borrelia spp. infections in ticks was 13% (116/910), and over 73% (85/116) were positively confirmed as being Borrelia crocidurae. Borreliosis cases accounted for 12% (94/800) of episodes of fever and all age groups were infected, with children and young people between the ages of 8-14 and 22-28 being the most infected by the disease (16% and 18.4%). TBRF cases occurred in all seasons, with a peak in August. In two species of small rodents that were found to be infected (Arvicanthis niloticus, Mus musculus), the proportion of Borrelia infection was 17.5% (10/57), and the highest prevalence of infection (40.9%, 9/22) was observed in A. niloticus. Our study indicates that TBRF is an endemic disease in the Niakhar district, where children and young people are the most infected. Arvicanthis niloticus and O. sonrai ticks are massively present and appear to be the main epidemiological reservoirs causing its extensive spread to humans.

Borrelia persica is the causative agent of tick-borne relapsing fever in Israel and is prevalent in the Eastern Mediterranean basin and parts of Asia. Infection with B. persica causes severe illness and potentially life-threatening complications in humans and companion animals. Isolation and in vitro cultivation of B. persica in culture medium is difficult and there are only two previous isolates of this spirochete. Here, we describe the first cultivation of B. persica from an ill dog. Isolation from the dog’s blood was performed with the Pettenkofer-LMU Bp medium and spirochetes with vibrant motility and cell density of 2 × 106/ml were observed in culture by dark-field microscopy 3 days after sampling. The isolate was passaged every 3–4 days with cell densities reaching up to 3 × 107/ml achieved over 30 passages. Cryopreservation was made at −80°C without any cryoprotectant additive, and successful growth from thawed culture samples was observed up to 3 months after freezing with repeated freeze and thaw cycles. Generation time during the exponential growth phase was 14.6 hr. Genetic characterization by polymerase chain reaction amplification and DNA sequencing of the flagellin, glycerophosphodiester phosphodiesterase, and 16S rRNA genes indicated that the isolate is a B. persica genotype I strain associated with human relapsing fever. The new canine isolate would be helpful for research on the pathogenesis of relapsing fever and the new modifications in cultivation and preservation methods may assist in future studies of relapsing fever by simplifying previously reported in vitro methods.

Abstract Background In the United States, Tick-Borne Relapsing Fever (TBRF) in dogs is caused by the spirochete bacteria Borrelia turicatae and Borrelia hermsii, transmitted by Ornithodoros spp. ticks. The hallmark diagnostic feature of this infection is the visualization of numerous spirochetes during standard blood smear examination. Although the course of spirochetemia has not been fully characterized in dogs, in humans infected with TBRF the episodes of spirochetemia and fever are intermittent. Objectives To describe TBRF in dogs by providing additional case reports and reviewing the disease in veterinary and human medicine. Animals Five cases of privately-owned dogs naturally infected with TBRF in Texas are reviewed. Methods Case series and literature review. Results All dogs were examined because of lethargy, inappetence, and pyrexia. Two dogs also had signs of neurologic disease. All dogs had thrombocytopenia and spirochetemia. All cases were administered tetracyclines orally. Platelet numbers improved and spirochetemia and pyrexia resolved in 4 out of 5 dogs, where follow-up information was available. Conclusion and Clinical Importance TBRF is likely underdiagnosed in veterinary medicine. In areas endemic to Ornithodoros spp. ticks, TBRF should be considered in dogs with thrombocytopenia. Examination of standard blood smears can provide a rapid and specific diagnosis of TBRF when spirochetes are observed.