Incidence of tick-borne relapsing fever in west Africa: longitudinal study

Development and validation of systems for genetic manipulation of the Old World tick-borne relapsing fever spirochete, Borrelia duttonii

Relapsing fever (RF), a vector-borne disease caused by Borrelia spp., is characterized by recurring febrile episodes due to repeated bouts of bacteremia. RF spirochetes can be geographically and phylogenetically divided into two distinct groups; Old World RF Borrelia (found in Africa, Asia, and Europe) and New World RF Borrelia (found in the Americas). While RF is a rarely reported disease in the Americas, RF is prevalent in endemic parts of Africa. Despite phylogenetic differences between Old World and New World RF Borrelia and higher incidence of disease associated with Old World RF spirochete infection, genetic manipulation has only been described in New World RF bacteria. Herein, we report the generation of genetic tools for use in the Old World RF spirochete, Borrelia duttonii. We describe methods for transformation and establish shuttle vector- and integration-based approaches for genetic complementation, creating green fluorescent protein (gfp)-expressing B. duttonii strains as a proof of principle. Allelic exchange mutagenesis was also used to inactivate a homolog of the Borrelia burgdorferi p66 gene, which encodes an important virulence factor, in B. duttonii and demonstrate that this mutant was attenuated in a murine model of RF. Finally, the B. duttonii p66 mutant was complemented using shuttle vector- and cis integration-based approaches. As expected, complemented p66 mutant strains were fully infectious, confirming that P66 is required for optimal mammalian infection. The genetic tools and techniques reported herein represent an important advancement in the study of RF Borrelia that allows for future characterization of virulence determinants and colonization factors important for the enzootic cycle of Old World RF spirochetes.

Neglected etiologies of prolonged febrile illnesses in tropical and subtropical regions: A systematic review

BACKGROUND

Febrile illnesses that persist despite initial treatment are common clinical challenges in (sub)tropical low-resource settings. Our aim is to review infectious etiologies of "prolonged fevers" (persistent febrile illnesses, PFI) and to quantify relative contributions of selected neglected target diseases with limited diagnostic options, often overlooked, causing inadequate antibiotic prescriptions, or requiring prolonged and potentially toxic treatments.

METHODS

We performed a systematic review of articles addressing the infectious etiologies of PFI in adults and children in sub-/tropical low- and middle-income countries (LMICs) using the PRISMA guidelines. A list of target diseases, including neglected parasites and zoonotic bacteria (e.g., Leishmania and Brucella), were identified by infectious diseases and tropical medicine specialists and prioritized in the search. Malaria and tuberculosis (TB) were not included as target diseases due to well-established epidemiology and diagnostic options. Four co-investigators independently extracted data from the identified articles while assessing for risk of bias.

RESULTS

196 articles from 52 countries were included, 117 from Africa (33 countries), 71 from Asia (16 countries), and 8 from Central and -South America (3 countries). Target diseases were reported as the cause of PFI in almost half of the articles, most frequently rickettsioses (including scrub typhus), relapsing fever borreliosis (RF-borreliosis), brucellosis, enteric fever, leptospirosis, Q fever and leishmaniasis. Among those, RF-borreliosis was by far the most frequently reported disease in Africa, particularly in Eastern Africa. Rickettsioses (including scrub typhus) were often described in both Africa and Asia. Leishmaniasis, toxoplasmosis and amoebiasis were the most frequent parasitic etiologies. Non-target diseases and non-tropical organisms (Streptococcus pneumoniae, Escherichia coli, and non-typhoidal Salmonella spp) were documented in a fifth of articles.

CONCLUSIONS

Clinicians faced with PFI in sub-/tropical LMICs should consider a wide differential diagnosis including enteric fever and zoonotic bacterial diseases (e.g., rickettsiosis, RF-borreliosis and brucellosis), or parasite infections (e.g., leishmaniasis) depending on geography and syndromes. In the absence of adequate diagnostic capacity, a trial of antibiotics targeting relevant intra-cellular bacteria, such as doxycycline or azithromycin, may be considered.

The global distribution and the risk prediction of relapsing fever group Borrelia: a data review with modelling analysis

BACKGROUND

The recent discovery of emerging relapsing fever group Borrelia (RFGB) species, such as Borrelia miyamotoi, poses a growing threat to public health. However, the global distribution and associated risk burden of these species remain uncertain. We aimed to map the diversity, distribution, and potential infection risk of RFGB.

METHODS

We searched PubMed, Web of Science, GenBank, CNKI, and eLibrary from Jan 1, 1874, to Dec 31, 2022, for published articles without language restriction to extract distribution data for RFGB detection in vectors, animals, and humans, and clinical information about human patients. Only articles documenting RFGB infection events were included in this study, and data for RFGB detection in vectors, animals, or humans were composed into a dataset. We used three machine learning algorithms (boosted regression trees, random forest, and least absolute shrinkage and selection operator logistic regression) to assess the environmental, ecoclimatic, biological, and socioeconomic factors associated with the occurrence of four major RFGB species: Borrelia miyamotoi, Borrelia lonestari, Borrelia crocidurae, and Borrelia hermsii; and mapped their worldwide risk level.

FINDINGS

We retrieved 13 959 unique studies, among which 697 met the selection criteria and were used for data extraction. 29 RFGB species have been recorded worldwide, of which 27 have been identified from 63 tick species, 12 from 61 wild animals, and ten from domestic animals. 16 RFGB species caused human infection, with a cumulative count of 26 583 cases reported from Jan 1, 1874, to Dec 31, 2022. Borrelia recurrentis (17 084 cases) and Borrelia persica (2045 cases) accounted for the highest proportion of human infection. B miyamotoi showed the widest distribution among all RFGB, with a predicted environmentally suitable area of 6·92 million km2, followed by B lonestari (1·69 million km2), B crocidurae (1·67 million km2), and B hermsii (1·48 million km2). The habitat suitability index of vector ticks and climatic factors, such as the annual mean temperature, have the most significant effect among all predictive models for the geographical distribution of the four major RFGB species.

INTERPRETATION

The predicted high-risk regions are considerably larger than in previous reports. Identification, surveillance, and diagnosis of RFGB infections should be prioritised in high-risk areas, especially within low-income regions.

FUNDING

National Key Research and Development Program of China.

Investigating the etiologies of non-malarial febrile illness in Senegal using metagenomic sequencing

The worldwide decline in malaria incidence is revealing the extensive burden of non-malarial febrile illness (NMFI), which remains poorly understood and difficult to diagnose. To characterize NMFI in Senegal, we collected venous blood and clinical metadata in a cross-sectional study of febrile patients and healthy controls in a low malaria burden area. Using 16S and untargeted sequencing, we detected viral, bacterial, or eukaryotic pathogens in 23% (38/163) of NMFI cases. Bacteria were the most common, with relapsing fever Borrelia and spotted fever Rickettsia found in 15.5% and 3.8% of cases, respectively. Four viral pathogens were found in a total of 7 febrile cases (3.5%). Sequencing also detected undiagnosed Plasmodium, including one putative P. ovale infection. We developed a logistic regression model that can distinguish Borrelia from NMFIs with similar presentation based on symptoms and vital signs (F1 score: 0.823). These results highlight the challenge and importance of improved diagnostics, especially for Borrelia, to support diagnosis and surveillance.

Tick-Borne Diseases of Humans and Animals in West Africa

Ticks are a significant group of arthropod vectors that transmit a large variety of pathogens responsible for human and animal diseases worldwide. Ticks are the second biggest transmitters of vector-borne diseases, behind mosquitoes. However, in West Africa, there is often only limited knowledge of tick-borne diseases. With the scarcity of appropriate diagnostic services, the prevalence of tick-borne diseases is generally underestimated in humans. In this review, we provide an update on tick-borne pathogens reported in people, animals and ticks in West Africa by microscopic, immunological and molecular methods. A systematic search was conducted in PubMed and Google Scholar. The selection criteria included all studies conducted in West Africa reporting the presence of Rickettsia, Borrelia, Anaplasma, Ehrlichia, Bartonella, Coxiella burnetii, Theileria, Babesia, Hepatozoon and Crimean-Congo haemorrhagic fever viruses in humans, animals or ticks. Our intention is to raise awareness of tick-borne diseases amongst human and animal health workers in West Africa, and also physicians working with tourists who have travelled to the region.

Improving diagnosis of non-malarial fevers in Senegal: Borrelia and the contribution of tick-borne bacteria

The worldwide decline in malaria incidence is revealing the extensive burden of non-malarial febrile illness (NMFI), which remains poorly understood and difficult to diagnose. To characterize NMFI in Senegal, we collected venous blood and clinical metadata from febrile patients and healthy controls in a low malaria burden area. Using 16S and unbiased sequencing, we detected viral, bacterial, or eukaryotic pathogens in 29% of NMFI cases. Bacteria were the most common, with relapsing fever Borrelia and spotted fever Rickettsia found in 15% and 3.7% of cases, respectively. Four viral pathogens were found in a total of 7 febrile cases (3.5%). Sequencing also detected undiagnosed Plasmodium, including one putative P. ovale infection. We developed a logistic regression model to distinguish Borrelia from NMFIs with similar presentation based on symptoms and vital signs. These results highlight the challenge and importance of improved diagnostics, especially for Borrelia, to support diagnosis and surveillance.

Ornithodoros sonrai Soft Ticks and Associated Bacteria in Senegal

The soft ticks, Ornithodoros sonrai, are known as vectors of the tick-borne relapsing fever caused by Borrelia spp. and have also been reported to carry other micro-organisms. The objective of this study was to collect and to identify O. sonrai ticks and to investigate the micro-organisms associated with them. In 2019, an investigation of burrows within human dwellings was conducted in 17 villages in the Niakhar area and in 15 villages in the Sine-Saloum area in the Fatick region of Senegal. Ticks collected from the burrows were identified morphologically and by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Micro-organism screening was performed by bacteria-specific qPCR and some identifications were made by standard PCR and gene sequencing. O. sonrai ticks were found in 100% (17/17) of the villages surveyed in the Niakhar area and in 66% (10/15) of the villages in the Sine-Saloum area. A total of 1275 soft tick specimens were collected from small mammal burrows. The ticks collected were morphologically identified as O. sonrai. About 20% (259/1275) of the specimens were also submitted to MALDI-TOF MS for identification. Among the resulting MS profiles, 87% (139/159) and 95% (95/100) were considered good quality specimens, preserved in alcohol and silica gel, respectively. All spectra of good quality were tested against our MALDI-TOF MS arthropod spectra database and identified as O. sonrai species, corroborating the morphological classification. The carriage of four micro-organisms was detected in the ticks with a high prevalence of Bartonella spp., Anaplasmataceae, and Borrelia spp. of 35, 28, and 26%, respectively, and low carriage of Coxiella burnetii (2%). This study highlights the level of tick infestation in domestic burrows, the inventory of pathogens associated with the O. sonrai tick, and the concern about the potential risk of tick involvement in the transmission of these pathogens in Senegal.

Pathogen Detection in Ornithodoros sonrai Ticks and Invasive House Mice Mus musculus domesticus in Senegal

Ornithodoros sonrai (O. sonrai) ticks are the only known vectors of Borrelia crocidurae, an agent of tick-borne relapsing fever (TBRF) borreliosis. Rodents serve as principal natural reservoirs for Borrelia. Our research objective was to detect TBRF Borrelia and other zoonotic bacterial infections in ticks and in house mice Mus musculus domesticus, an invasive species currently expanding in rural northern Senegal. Real-time and conventional PCR were utilized for detecting Borrelia and other bacterial taxa. The analyses were performed on 253 specimens of O. sonrai and 150 samples of brain and spleen tissue from rodents. Borrelia crocidurae was found in one O. sonrai tick and 18 Mus musculus domesticus samples, with prevalences of 0.39 percent and 12 percent, respectively, as well as Ehrlichia sp. in one Mus musculus domesticus. Further, we were able to detect the presence of a potentially infectious novel species belonging to the Anaplasmataceae family for the first time in O. sonrai ticks. More attention should be paid to the house mouse and O. sonrai ticks, as they can be potential hosts for novel species of pathogenic bacteria in humans.

CD55 Facilitates Immune Evasion by Borrelia crocidurae, an Agent of Relapsing Fever

Relapsing fever, caused by diverse Borrelia spirochetes, is prevalent in many parts of the world and causes significant morbidity and mortality. To investigate the pathoetiology of relapsing fever, we performed a high-throughput screen of Borrelia-binding host factors using a library of human extracellular and secretory proteins and identified CD55 as a novel host binding partner of Borrelia crocidurae and Borrelia persica, two agents of relapsing fever in Africa and Eurasia. CD55 is present on the surface of erythrocytes, carries the Cromer blood group antigens, and protects cells from complement-mediated lysis. Using flow cytometry, we confirmed that both human and murine CD55 bound to B. crocidurae and B. persica. Given the expression of CD55 on erythrocytes, we investigated the role of CD55 in pathological B. crocidurae-induced erythrocyte aggregation (rosettes), which enables spirochete immune evasion. We showed that rosette formation was partially dependent on host cell CD55 expression. Pharmacologically, soluble recombinant CD55 inhibited erythrocyte rosette formation. Finally, CD55-deficient mice infected with B. crocidurae had a lower pathogen load and elevated proinflammatory cytokine and complement factor C5a levels. In summary, our results indicate that CD55 is a host factor that is manipulated by the causative agents of relapsing fever for immune evasion. IMPORTANCE Borrelia species are causative agents of Lyme disease and relapsing fever infections in humans. B. crocidurae causes one of the most prevalent relapsing fever infections in parts of West Africa. In the endemic regions, B. crocidurae is present in ~17% of the ticks and ~11% of the rodents that serve as reservoirs. In Senegal, ~7% of patients with acute febrile illness were found to be infected with B. crocidurae. There is little information on host-pathogen interactions and how B. crocidurae manipulates host immunity. In this study, we used a high-throughput screen to identify host proteins that interact with relapsing fever-causing Borrelia species. We identified CD55 as one of the host proteins that bind to B. crocidurae and B. persica, the two causes of relapsing fever in Africa and Eurasia. We show that the interaction of B. crocidurae with CD55, present on the surface of erythrocytes, is key to immune evasion and successful infection in vivo. Our study further shows the role of CD55 in complement regulation, regulation of inflammatory cytokine levels, and innate immunity during relapsing fever infection. Overall, this study sheds light on host-pathogen interactions during relapsing fever infection in vivo.

Characterization of Immunological Responses to Borrelia Immunogenic Protein A (BipA), a Species-Specific Antigen for North American Tick-Borne Relapsing Fever

Tick-borne relapsing fever (TBRF) is a neglected vector-borne bacterial disease distributed worldwide. Borrelia turicatae, Borrelia parkeri, and Borrelia hermsii are three argasid-borne TBRF species previously implicated in human disease in North America. TBRF is likely underdiagnosed due to its nonspecific symptoms and poorly developed diagnostic tests. Studies suggest that the Borrelia immunogenic protein A (BipA) is specific to TBRF Borrelia but heterogenic between species. In this study, we hypothesized that antibody responses generated to BipA are specific to the North American TBRF species infecting a given animal. To test this, we characterized the expression and localization of native BipA in North American species of TBRF Borrelia. We also infected mice by needle inoculation or tick bite with B. turicatae, B. hermsii, or B. parkeri and evaluated serum sample reactivity to recombinant BipA (rBipA) that was produced from each species. Furthermore, serum samples from nonhuman primates and domestic dogs experimentally infected with B. turicatae were assessed. Lastly, we tested human Lyme disease (LD) serum samples to determine potential cross-reactivity to rBipA generated from B. turicatae, B. parkeri, and B. hermsii. Our findings indicate that rBipA has the potential to distinguish between infections of LD- and TBRF-causing spirochetes and that antibody responses were more robust toward the Borrelia species causing infection. This work further supports that rBipA can likely distinguish between B. turicatae, B. hermsii, and B. parkeri infections in mice, canines, and nonhuman primates. IMPORTANCEBorrelia species transmitted by soft or hard ticks cause tick-borne relapsing fever (TBRF). This is a debilitating disease distributed worldwide but is likely underdiagnosed or misdiagnosed as Lyme disease due to poorly developed diagnostic tests. Borrelia turicatae, Borrelia parkeri, and Borrelia hermsii are three TBRF species previously implicated in human disease in North America. Commonly used diagnostic methods do not identify the species causing infection. In this study, we evaluated the potential of recombinant Borrelia immunogenic protein A (rBipA) as a diagnostic antigen capable of distinguishing between infections of TBRF Borrelia species. We show that serum from mice, canines, and nonhuman primates infected with B. turicatae, B. parkeri, or B. hermsii react more strongly to the rBipA from the species causing infection. Furthermore, sera from Lyme disease patients failed to cross-react with our rBipA proteins, indicating the potential to use rBipA as a species-specific diagnostic antigen for TBRF.

Molecular characterization of some equine vector-borne diseases and associated arthropods in Egypt

Equine vector-borne diseases (EVBDs) are emerging and re-emerging diseases, and most of them are zoonotic. This study aimed to investigate EVBDs in equines and associated arthropods (ticks and flies) from Egypt using molecular analyses, in addition to a preliminary characterization of associated ticks and flies by the matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) and molecular techniques. In this study, 335 blood samples were obtained from equines that appeared to be in good health (320 horses and 15 donkeys) in Cairo and Beni Suef provinces, Egypt. From the same animals, 166 arthropods (105 sucking flies and 61 ticks) were collected. Ticks and flies were preliminary characterized by the MALDI-TOF and molecular tools. Quantitative PCR (qPCR) and standard PCR coupled with sequencing were performed on the DNA of equines, ticks, and flies to screen multiple pathogens. The MALDI-TOF and molecular characterization of arthropods revealed that louse fly (Hippobosca equina) and cattle tick (Rhipicephalus annulatus) infesting equines. Anaplasma platys-like (1.6%), Anaplasma marginale (1.6%), Candidatus Ehrlichia rustica (6.6%), a new Ehrlichia sp. (4.9%), and Borrelia theileri (3.3%) were identified in R. annulatus. Anaplasma sp. and Borrelia sp. DNAs were only detected in H. equina by qPCR. A. marginale, Anaplasma ovis, and Theileria ovis recorded the same low infection rate (0.6%) in donkeys, while horses were found to be infected with Theileria equi and a new Theileria sp. Africa with recorded prevalence rates of 1.2% and 2.7%, respectively. In conclusion, different pathogens were first detected such as A. platys-like, Candidatus E. rustica, and a new Ehrlichia sp. in R. annulatus; A. marginale, A. ovis, and T. ovis in donkeys; and a new Theileria sp. "Africa" in horses.

Tick borne relapsing fever - a systematic review and analysis of the literature

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.

Molecular and MALDI-TOF MS characterisation of Hyalomma aegyptium ticks collected from turtles and their associated microorganisms in Algeria

The identification of ticks and their associated pathogens is important for knowledge on tick-borne diseases. The objective of this study was to use morphological, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and/or molecular biology tools to identify ticks collected from turtles in north-eastern Algeria, as well as to investigate the microorganisms associated with these ticks. A total of 471 adult ticks were collected and identified morphologically as Hyalomma aegyptium, of which 248 (52.7%) were female and 223 (47.3%) were male. amongst them, 230 specimens were randomly selected for molecular and MALDI-TOF MS analysis. Molecular biology confirmed that our ticks were Hy. aegyptium. MALDI-TOF MS analysis revealed that 100% of the spectra were of excellent quality. Four spectra were selected to update our own database MALDI-TOF MS arthropod. The blind test of the 226 remaining spectra showed that all ticks were correctly identified, with scores ranging from 1.774 to 2.655 with a mean of 2.271 ± 0.16 of which, 223 (98.6%) had log score value (LSV)>1.8. Molecular biology screening showed that the ticks carried the DNA of Borrelia turcica, Rickettsia africae, Rickettsia aeschlimannii, Rickettsia sibirica mongolitimonae and with the Anaplasmataceae were close to a potentially new, undescribed Ehrlichia sp. This study confirms that MALDI-TOF MS is a reliable tool for the identification of ticks and that ticks collected from turtles in Algeria are carriers of several species of microorganisms which may be responsible for diseases in humans and animals.

Borrelia duttonii-like spirochetes parasitize Meriones persicus in East Azerbaijan Province of Iran

In Iran, Borrelia persica and Borrelia microti/microti-like borreliae have been established as causative agents of tickborne relapsing fever (TBRF). However, the epidemiology of two previously described species, Borrelia balthazardi and Borrelia latyschewii (latychevi), has remained elusive for many years. We investigated Borrelia infection in various rodents and small mammals in the TBRF endemic East Azerbaijan Province, northwestern Iran, where B. perisca and B. balthazardi might coexist. Among trapped animals (n=210), a 16S real-time PCR detected Borrelia DNA in 11 Meriones persicus. Multilocus sequence analysis (MLSA) using six different loci, including four coding regions (flaB, glpQ, groEL, p66) and two non-coding (rrs, IGS) followed by phylogeny revealed considerable sequence identity between the borreliae detected, B. microti, and East African Borrelia duttonii, and Borrelia recurrentis. Our results indicate that B. microti and microti-like borreliae, including the specimens previously characterized in the south of Iran and the present study, are different ecotypes of B. duttonii, i.e., exhibiting a single species/entity or descendants of a recent common ancestor. Our findings also suggest that the species we had long coined as B. balthazardi and the microti-like borreliae detected herein might be the same.

Detection of Coxiella burnetii and Borrelia spp. DNA in Cutaneous Samples and in Household Dust in Rural Areas, Senegal

Q fever and tick-borne borreliosis are two zoonotic diseases rarely diagnosed in Senegalese health facilities, particularly in rural areas. Our study aims to better understand the circulation of Coxiella burnetii and Borrelia spp. DNA on human skin and the domestic environment in rural areas. Cutaneous swabs were taken from febrile patients being treated for borreliosis and/or Q fever, the members of patients' households and control households in the Niakhar area. Dust samples were also collected from 90 households where 54 cases of borreliosis and Q fever were reported as well as from the households of members of control populations in Dielmo, Ndiop, and Niakhar. C. burnetii and Borrelia spp. DNA were detected by quantitative PCR in cutaneous swabs and dust samples targeting spacers IS1111_IS30A and Bor 16S gene. Of 1365 persons tested, 76 were shown to carry C. burnetii, 13 Borrelia spp., and 6 were identified as carrying both C. burnetii and Borrelia spp. The prevalence of Borrelia spp. DNA in households was 16.7% in Dielmo, 6.7% in Ndiop, and 23.3% in all other villages in the Niakhar area, and the presence of C. burnetii in the same localities was 10%, 13.3% and 66.7%, respectively. Furthermore, C. burnetii genotyping identified the presence of Multispacer Sequence Typing group 6. These results revealed for the first time the carriage on the skin of C. burnetii and Borrelia spp. DNA in humans and its wide distribution across households. Our findings suggest that many populations are exposed to these diseases, with frequent contaminating cases of infectious origin arising from the domestic environment.

Morphological, molecular and MALDI-TOF MS identification of ticks and tick-associated pathogens in Vietnam

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been reported as a promising and reliable tool for arthropod identification, including the identification of alcohol-preserved ticks based on extracted leg protein spectra. In this study, the legs of 361 ticks collected in Vietnam, including 251 Rhiphicephalus sanguineus s.l, 99 Rhipicephalus (Boophilus) microplus, two Amblyomma varanensis, seven Dermacentor auratus, one Dermacentor compactus and one Amblyomma sp. were submitted for MALDI-TOF MS analyses. Spectral analysis showed intra-species reproducibility and inter-species specificity and the spectra of 329 (91%) specimens were of excellent quality. The blind test of 310 spectra remaining after updating the database with 19 spectra revealed that all were correctly identified with log score values (LSV) ranging from 1.7 to 2.396 with a mean of 1.982 ± 0.142 and a median of 1.971. The DNA of several microorganisms including Anaplasma platys, Anaplasma phagocytophilum, Anaplasma marginale, Ehrlichia rustica, Babesia vogeli, Theileria sinensis, and Theileria orientalis were detected in 25 ticks. Co-infection by A. phagocytophilum and T. sinensis was found in one Rh. (B) microplus.

Simultaneous Detection and Differentiation of Clinically Relevant Relapsing Fever Borrelia with Semimultiplex Real-Time PCR

Bacterial vector-borne diseases, including Borrelia species, present a significant diagnostic, clinical, and public health challenge due to their overlapping symptoms and the breadth of causative agents and arthropod vectors. The relapsing fever (RF) borreliae encompass both established and emerging pathogens and are transmitted to humans by soft ticks, hard ticks, or lice. We developed a real-time semimultiplex PCR assay that detects multiple RF borreliae causing human illness and classifies them into one of three groups. The groups are based on genetic similarity and include agents of soft-tick relapsing fever (Borrelia hermsii and others), the emerging hard-tick-transmitted pathogen B. miyamotoi, and the agent of louse-borne relapsing fever (B. recurrentis). The real-time PCR assay uses a single primer pair designed to amplify all known pathogenic RF borreliae and multiple TaqMan probes to allow the detection of and differentiation among the three groups. The assay detects all RF borreliae tested, with an analytical limit of detection below 15 genome equivalents per reaction. Thirty isolates of RF borreliae encompassing six species were accurately identified. Thirty-nine of 41 residual specimens (EDTA whole blood, serum, or plasma) from patients with RF were detected and correctly classified. None of 42 clinical samples from patients with other infections and 46 culture specimens from non-RF bacteria were detected. The development of a single-assay real-time PCR approach will help to improve the diagnosis of RF by simplifying the selection of tests to aid in the clinical management of acutely ill RF patients.

The Diadenylate Cyclase CdaA Is Critical for Borrelia turicatae Virulence and Physiology

Relapsing fever (RF), caused by spirochetes of the genus Borrelia, is a globally distributed, vector-borne disease with high prevalence in developing countries. To date, signaling pathways required for infection and virulence of RF Borrelia spirochetes are unknown. Cyclic di-AMP (c-di-AMP), synthesized by diadenylate cyclases (DACs), is a second messenger predominantly found in Gram-positive organisms that is linked to virulence and essential physiological processes. Although Borrelia is Gram-negative, it encodes one DAC (CdaA), and its importance remains undefined. To investigate the contribution of c-di-AMP signaling in the RF bacterium Borrelia turicatae, a cdaA mutant was generated. The mutant was significantly attenuated during murine infection, and genetic complementation reversed this phenotype. Because c-di-AMP is essential for viability in many bacteria, whole-genome sequencing was performed on cdaA mutants, and single-nucleotide polymorphisms identified potential suppressor mutations. Additionally, conditional mutation of cdaA confirmed that CdaA is important for normal growth and physiology. Interestingly, mutation of cdaA did not affect expression of homologs of virulence regulators whose levels are impacted by c-di-AMP signaling in the Lyme disease bacterium Borrelia burgdorferi Finally, the cdaA mutant had a significant growth defect when grown with salts, at decreased osmolarity, and without pyruvate. While the salt treatment phenotype was not reversed by genetic complementation, possibly due to suppressor mutations, growth defects at decreased osmolarity and in media lacking pyruvate could be attributed directly to cdaA inactivation. Overall, these results indicate CdaA is critical for B. turicatae pathogenesis and link c-di-AMP to osmoregulation and central metabolism in RF spirochetes.

Tick-borne relapsing fever Borreliosis, a major public health problem overlooked in Senegal

BACKGROUND

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.

METHODOLOGY/PRINCIPAL FINDINGS

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.

CONCLUSION/SIGNIFICANCE

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.

Perpetuation of Borreliae

With one exception (epidemic relapsing fever), borreliae are obligately maintained in nature by ticks. Although some Borrelia spp. may be vertically transmitted to subsequent generations of ticks, most require amplification by a vertebrate host because inheritance is not stable. Enzootic cycles of borreliae have been found globally; those receiving the most attention from researchers are those whose vectors have some degree of anthropophily and, thus, cause zoonoses such as Lyme disease or relapsing fever. To some extent, our views on the synecology of the borreliae has been dominated by an applied focus, viz., analyses that seek to understand the elements of human risk for borreliosis. But, the elements of borrelial perpetuation do not necessarily bear upon risk, nor do our concepts of risk provide the best structure for analyzing perpetuation. We identify the major global themes for the perpetuation of borreliae, and summarize local variations on those themes, focusing on key literature to outline the factors that serve as the basis for the distribution and abundance of borreliae.

Rodents as Hosts of Pathogens and Related Zoonotic Disease Risk

Rodents are known to be reservoir hosts for at least 60 zoonotic diseases and are known to play an important role in their transmission and spread in different ways. We sampled different rodent communities within and around human settlements in Northern Senegal, an area subjected to major environmental transformations associated with global changes. Herein, we conducted an epidemiological study on their bacterial communities. One hundred and seventy-one (171) invasive and native rodents were captured, 50 from outdoor trapping sites and 121 rodents from indoor habitats, consisting of five species. The DNA of thirteen pathogens was successfully screened on the rodents' spleens. We found: 2.3% of spleens positive to Piroplasmida and amplified one which gave a potentially new species Candidatus "Theileria senegalensis"; 9.35% of Bartonella spp. and amplified 10, giving three genotypes; 3.5% of filariasis species; 18.12% of Anaplasmataceae species and amplified only 5, giving a new potential species Candidatus "Ehrlichia senegalensis"; 2.33% of Hepatozoon spp.; 3.5% of Kinetoplastidae spp.; and 15.2% of Borrelia spp. and amplified 8 belonging all to Borrelia crocidurae. Some of the species of pathogens carried by the rodents of our studied area may be unknown because most of those we have identified are new species. In one bacterial taxon, Anaplasma, a positive correlation between host body mass and infection was found. Overall, male and invasive rodents appeared less infected than female and native ones, respectively.

Host Competency of the Multimammate Rat Mastomys natalensis Demonstrated by Prolonged Spirochetemias with the African Relapsing Fever Spirochete Borrelia crocidurae

African multimammate rats, Mastomys natalensis, are widely distributed in sub-Saharan Africa and live in close association with humans. In West Africa, numerous field studies have shown these animals may be naturally infected with the relapsing fever spirochete Borrelia crocidurae, the primary cause of tick-borne relapsing fever in this region of the continent. However, naturally infected individual rats have never been examined over time; therefore, the true host competency of these rats for this spirochete is unknown. Therefore, using animals from an established laboratory colony of M. natalensis, rats were experimentally infected with B. crocidurae and their blood examined to 28 days postinoculation. These animals were highly susceptible to infection and displayed prolonged and cyclic spirochetemias. Our results demonstrate these peridomestic rodents are likely competent hosts for infecting argasid tick vectors and play a primary role in the enzootic cycle for B. crocidurae in West Africa.

Assessing the Contribution of an HtrA Family Serine Protease During Borrelia turicatae Mammalian Infection

Tick-borne relapsing fever (TBRF), characterized by recurring febrile episodes, is globally distributed and among the most common bacterial infections in some African countries. Despite the public health concern that this disease represents, little is known regarding the virulence determinants required by TBRF Borrelia during infection. Because the chromosomes of TBRF Borrelia show extensive colinearity with those of Lyme disease (LD) Borrelia, the exceptions represent unique genes encoding proteins that are potentially essential to the disparate enzootic cycles of these two groups of spirochetes. One such exception is a gene encoding an HtrA family protease, BtpA, that is present in TBRF Borrelia, but not in LD spirochetes. Previous work suggested that btpA orthologs may be important for resistance to stresses faced during mammalian infection. Herein, proteomic analyses of the TBRF spirochete, Borrelia turicatae, demonstrated that BtpA, as well as proteins encoded by adjacent genes in the B. turicatae genome, were produced in response to culture at mammalian body temperature, suggesting a role in mammalian infection. Further, transcriptional analyses revealed that btpA was expressed with the genes immediately upstream and downstream as part of an operon. To directly assess if btpA is involved in resistance to environmental stresses, btpA deletion mutants were generated. btpA mutants demonstrated no growth defect in response to heat shock, but were more sensitive to oxidative stress produced by t-butyl peroxide compared to wild-type B. turicatae. Finally, btpA mutants were fully infectious in a murine relapsing fever (RF) infection model. These results indicate that BtpA is either not required for mammalian infection, or that compensatory mechanisms exist in TBRF spirochetes to combat environmental stresses encountered during mammalian infection in the absence of BtpA.

Tick-borne relapsing fever as a potential veterinary medical problem

Tick-borne relapsing fever (TBRF) caused by the bacteria Borrelia, is poorly documented in veterinary medicine. Given the widespread presence of the soft tick vectors - Ornithodoros and the recently discovered hard tick vectors, as well as their close association with animal hosts, it is highly likely that infection occurs, but is rarely reported to be of veterinary importance. Sporadic reports of canine infection, some being fatal through to probable cause of abortion in horses have been published. Some of these pathogens exist in regions where there are limited diagnostic facilities, hence, they are likely to be missed and their impact on productivity may be unquantified. Here we review available literatures on cases of TBRF in domestic and wild animals in order to show their potential veterinary medical impact. Future efforts using field and laboratory surveys are needed to determine pathogenesis, vector competence and distribution in animals, their impact on animal health and productivity as well as to prevent further spill to the human population, where it is already a public health problem in some parts of the world.

Ornithodoros savignyi, the Tick Vector of "Candidatus Borrelia kalaharica" in Nigeria

Endemic tick-borne relapsing fever (TBRF) has not been documented in Nigeria, yet clinically compatible cases have been described, and soft tick species are endemic in surrounding countries. Consequently, our aim was to investigate if TBRF-associated Borrelia is present in Nigeria. To address this, we examined 49 soft tick pools to identify the tick species and to screen for Borrelia The tick species was revealed by 16S rRNA gene amplification and Sanger sequencing to be Ornithodoros savignyi, an aggressive, multihost, rapidly feeding species with significant veterinary impact. We detected a Borrelia organism in 3 of 49 pooled samples (6%). Molecular analysis of amplified 16S rRNA and flagellin genes and intragenic spacer fragments disclosed that this Borrelia organism was synonymous with the recently described organism "Candidatus Borrelia kalaharica," identified in a tourist returning to Germany from South Africa. Given the widespread endemic range of this tick vector, TBRF should be considered part of the differential diagnosis for patients with fever returning from arid areas of Africa and further afield.

Developing Research in Infectious and Tropical Diseases in Africa: The Paradigm of Senegal

Infectious diseases represent one of the greatest potential barriers to achievement of the third Sustainable Development Goals in African countries and around the world because they continue to pose major public health challenges. The surveillance of infectious diseases has recently assumed greater importance in most African countries, both because of the emergence of infectious diseases and because strains of pathogens that cause tuberculosis, malaria, cholera, dysentery, and pneumonia have developed resistance to common and inexpensive antimicrobial drugs. However, data on the pathogen-specific causes of infectious diseases are limited. Developing research in infectious and tropical diseases in Africa is urgently needed to better describe the distribution of pathogen-borne diseases and to know which pathogens actually cause fever. This research is critical for guiding treatment and policies in Africa. More effective diagnostics are also needed for these diseases, which often are misdiagnosed or diagnosed too late. A comprehensive review of this type of research is presented here.

Reservoir and vector evolutionary pressures shaped the adaptation of Borrelia

The life cycle of spirochetes of the genus Borrelia includes complex networks of vertebrates and ticks. The tripartite association of Borrelia-vertebrate-tick has proved ecologically successful for these bacteria, which have become some of the most prominent tick-borne pathogens in the northern hemisphere. To keep evolutionary pace with its double-host life history, Borrelia must adapt to the evolutionary pressures exerted by both sets of hosts. In this review, we attempt to reconcile functional, phylogenetic, and ecological perspectives to propose a coherent scenario of Borrelia evolution. Available empirical information supports that the association of Borrelia with ticks is very old. The major split between the tick families Argasidae-Ixodidae (dated some 230-290 Mya) resulted in most relapsing fever (Rf) species being restricted to Argasidae and few associated with Ixodidae. A further key event produced the diversification of the Lyme borreliosis (Lb) species: the radiation of ticks of the genus Ixodes from the primitive stock of Ixodidae (around 217 Mya). The ecological interactions of Borrelia demonstrate that Argasidae-transmitted Rf species remain restricted to small niches of one tick species and few vertebrates. The evolutionary pressures on this group are consequently low, and speciation processes seem to be driven by geographical isolation. In contrast to Rf, Lb species circulate in nested networks of dozens of tick species and hundreds of vertebrate species. This greater variety confers a remarkably variable pool of evolutionary pressures, resulting in large speciation of the Lb group, where different species adapt to circulate through different groups of vertebrates. Available data, based on ospA and multilocus sequence typing (including eight concatenated in-house genes) phylogenetic trees, suggest that ticks could constitute a secondary bottleneck that contributes to Lb specialization. Both sets of adaptive pressures contribute to the resilience of highly adaptable meta-populations of bacteria.

Relapsing Fevers: Neglected Tick-Borne Diseases

Relapsing fever still remains a neglected disease and little is known on its reservoir, tick vector and physiopathology in the vertebrate host. The disease occurs in temperate as well as tropical countries. Relapsing fever borreliae are spirochaetes, members of the Borreliaceae family which also contain Lyme disease spirochaetes. They are mainly transmitted by Ornithodoros soft ticks, but some species are vectored by ixodid ticks. Traditionally a Borrelia species is associated with a specific vector in a particular geographical area. However, new species are regularly described, and taxonomical uncertainties deserve further investigations to better understand Borrelia vector/host adaptation. The medical importance of Borrelia miyamotoi, transmitted by Ixodes spp., has recently spawned new interest in this bacterial group. In this review, recent data on tick-host-pathogen interactions for tick-borne relapsing fevers is presented, with special focus on B. miyamotoi.

Genetic characterization of African swine fever virus isolates from soft ticks at the wildlife/domestic interface in Mozambique and identification of a novel genotype

African swine fever virus (ASFV) is one of the most threatening infectious diseases of pigs. There are not sufficient data to indicate the importance of the sylvatic cycle in the spread and maintenance of the disease locally and potentially, globally. To assess the capacity to maintain ASF in the environment, we investigated the presence of soft tickreservoirs of ASFV in Gorongosa National Park (GNP) and its surrounding villages. A total of 1,658 soft ticks were recovered from warthog burrows and pig pens at the wildlife/livestock interface of the GNP and viral DNA was confirmed by nested PCR in 19% of Ornithodoros porcinus porcinus and 15% of O. p. domesticus. However, isolation of ASFV was only achieved in approximately 50% of the PCR-positive samples with nineteen haemadsorbing virus isolates recovered. These were genotyped using a combination of partial sequencing of the B646L gene (p72) and analysis of the central variable region (CVR) of the B602L gene. Eleven isolates were classified as belonging to genotype II and homologous to contemporary isolates from southern Africa, the Indian Ocean and eastern Europe. Three isolates grouped within genotype V and were similar to previous isolates from Mozambique and Malawi. The remaining five isolates constituted a new, previously unidentified genotype, designated genotype XXIV. This work confirms for the first time that the virus currently circulating in eastern Europe is likely to have a wildlife origin, and that the large diversity of ASFV maintained in wildlife areas can act as a permanent sources of different strains for the domestic pig value chain in Mozambique and beyond its boundaries. Their genetic similarity to ASFV strains currently spreading across Europe justifies the need to continue studying the sylvatic cycle in this African country and other parts of southern Africa in order to identify potential hot spots of ASF emergence and target surveillance and control efforts.

Crystal Structure of Borrelia turicatae protein, BTA121, a differentially regulated gene in the tick-mammalian transmission cycle of relapsing fever spirochetes

Tick-borne relapsing fever (RF) borreliosis is a neglected disease that is often misdiagnosed. RF species circulating in the United States include Borrelia turicatae, which is transmitted by argasid ticks. Environmental adaptation by RF Borrelia is poorly understood, however our previous studies indicated differential regulation of B. turicatae genes localized on the 150 kb linear megaplasmid during the tick-mammalian transmission cycle, including bta121. This gene is up-regulated by B. turicatae in the tick versus the mammal, and the encoded protein (BTA121) is predicted to be surface localized. The structure of BTA121 was solved by single-wavelength anomalous dispersion (SAD) using selenomethionine-derivative protein. The topology of BTA121 is unique with four helical domains organized into two helical bundles. Due to the sequence similarity of several genes on the megaplasmid, BTA121 can serve as a model for their tertiary  structures. BTA121 has large interconnected tunnels and cavities that can accommodate ligands, notably long parallel helices, which have a large hydrophobic central pocket. Preliminary in-vitro studies suggest that BTA121 binds lipids, notably palmitate with a similar order of binding affinity as tablysin-15, a known palmitate-binding protein. The reported data will guide mechanistic studies to determine the role of BTA121 in the tick-mammalian transmission cycle of B. turicatae.

Ecological and sanitary impacts of bacterial communities associated to biological invasions in African commensal rodent communities

Changes in host-parasite ecological interactions during biological invasion events may affect both the outcome of invasions and the dynamics of exotic and/or endemic infections. We tested these hypotheses, by investigating ongoing house mouse (Mus musculus domesticus) and black rat (Rattus rattus) invasions in Senegal (West Africa). We used a 16S gene rRNA amplicon sequencing approach to study potentially zoonotic bacterial communities in invasive and native rodents sampled along two well-defined independent invasion routes. We found that individual host factors (body mass and sex) were important drivers of these bacterial infections in rodents. We observed that the bacterial communities varied along invasion routes and differed between invasive and native rodents, with native rodents displaying higher overall bacterial diversity than invasive rodents. Differences in prevalence levels for some bacterial Operational Taxonomic Units (OTUs) provided support for ecological processes connecting parasitism and invasion success. Finally, our results indicated that rodent invasions may lead to the introduction of exotic bacterial genera and/or to changes in the prevalence of endemic ones. This study illustrates the difficulty of predicting the relationship between biodiversity and disease risks, and advocate for public health prevention strategies based on global pathogen surveillance followed by accurate characterization of potential zoonotic agents.

Ecological niche modeling and distribution of Ornithodoros hermsi associated with tick-borne relapsing fever in western North America

Tick-borne relapsing fever in western North America is a zoonosis caused by the spirochete bacterium, Borrelia hermsii, which is transmitted by the bite of infected Ornithodoros hermsi ticks. The pathogen is maintained in natural cycles involving small rodent hosts such as chipmunks and tree squirrels, as well as the tick vector. In order for these ticks to establish sustained and viable populations, a narrow set of environmental parameters must exist, primarily moderate temperatures and moderate to high amounts of precipitation. Maximum Entropy Species Distribution Modeling (Maxent) was used to predict the species distribution of O. hermsi and B. hermsii through time and space based on current climatic trends and future projected climate changes. From this modeling process, we found that the projected current distributions of both the tick and spirochete align with known endemic foci for the disease. Further, global climate models predict a shift in the distribution of suitable habitat for the tick vector to higher elevations. Our predictions are useful for targeting surveillance efforts in areas of high risk in western North America, increasing the efficiency and accuracy of public health investigations and vector control efforts.

The model presented here provides valuable epidemiological information on tick-borne relapsing fever in western North America. The inference gleaned from these models represents areas where human infection with B. hermsii is likely to occur. The predicted distribution of O. hermsi and B. hermsii may allow health officials to decrease human disease burden by implementing targeted surveillance efforts, thus better utilizing resources. The models we created predict the current distribution of O. hermsi and B. hermsii, as well as the predicted distribution in 2050 under medium and high greenhouse gas (GHG) concentration trajectories. Understanding how the distribution of the pathogen and its vector expand or contract in response to GHG concentrations is necessary for understanding human risk of infection with this debilitating disease both now and in the future.

Diagnosis of Louse-Borne Relapsing Fever despite Negative Microscopy in Two Asylum Seekers from Eastern Africa

We report two cases of louse-borne relapsing fever observed at our Institution in June 2016. Both patients were young asylum seekers from Africa who had recently arrived in Milan, Italy. Notably, direct microscopic examination of peripheral blood smears was repeatedly negative for the presence of spirochetes and the diagnosis, supported by clinical and epidemiologic evidence, required molecular confirmation by polymerase chain reaction amplification of DNA extracted from blood and sequencing of the amplified products.

Molecular and MALDI-TOF identification of ticks and tick-associated bacteria in Mali

Ticks are considered the second vector of human and animal diseases after mosquitoes. Therefore, identification of ticks and associated pathogens is an important step in the management of these vectors. In recent years, Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been reported as a promising method for the identification of arthropods including ticks. The objective of this study was to improve the conditions for the preparation of tick samples for their identification by MALDI-TOF MS from field-collected ethanol-stored Malian samples and to evaluate the capacity of this technology to distinguish infected and uninfected ticks. A total of 1,333 ticks were collected from mammals in three distinct sites from Mali. Morphological identification allowed classification of ticks into 6 species including Amblyomma variegatum, Hyalomma truncatum, Hyalomma marginatum rufipes, Rhipicephalus (Boophilus) microplus, Rhipicephalus evertsi evertsi and Rhipicephalus sanguineus sl. Among those, 471 ticks were randomly selected for molecular and proteomic analyses. Tick legs submitted to MALDI-TOF MS revealed a concordant morpho/molecular identification of 99.6%. The inclusion in our MALDI-TOF MS arthropod database of MS reference spectra from ethanol-preserved tick leg specimens was required to obtain reliable identification. When tested by molecular tools, 76.6%, 37.6%, 20.8% and 1.1% of the specimens tested were positive for Rickettsia spp., Coxiella burnetii, Anaplasmataceae and Borrelia spp., respectively. These results support the fact that MALDI-TOF is a reliable tool for the identification of ticks conserved in alcohol and enhances knowledge about the diversity of tick species and pathogens transmitted by ticks circulating in Mali.

Bacterial arthropod-borne diseases in West Africa

Arthropods such as ticks, lice, fleas and mites are excellent vectors for many pathogenic agents including bacteria, protozoa and viruses to animals. Moreover, many of these pathogens can also be accidentally transmitted to humans throughout the world. Bacterial vector-borne diseases seem to be numerous and very important in human pathology, however, they are often ignored and are not well known. Yet they are in a phase of geographic expansion and play an important role in the etiology of febrile episodes in regions of Africa. Since the introduction of molecular techniques, the presence of these pathogens has been confirmed in various samples from arthropods and animals, and more rarely from human samples in West Africa. In this review, the aim is to summarize the latest information about vector-borne bacteria, focusing on West Africa from 2000 until today in order to better understand the epidemiological risks associated with these arthropods. This will allow health and veterinary authorities to develop a strategy for surveillance of arthropods and bacterial disease in order to protect people and animals.

Ixodoidea of the Western Palaearctic: A review of available literature for identification of species

We aim to produce a review of the most important literature references necessary for the identification of ticks of the families Ixodidae and Argasidae in Europe and northern Africa (i.e. the Western Palaearctic region). The purpose of this paper is to pinpoint a set of critically selected papers that contain reliable information on morphology, taxonomic keys, and comparative discussions which are critical for the identification of the ticks reported in the target region. When necessary, comments are provided on the systematic position of a species, or on suitable papers already addressing the issue. This review includes a list of 216 references which cover all Ixodoidea species reported as permanent residents of the Western Palaearctic, namely 28 species of the genus Ixodes, two Dermacentor, seven Haemaphysalis, nine Hyalomma, eight Rhipicephalus, five Argas and about seven species of Ornithodoros.

Plasmodium falciparum malaria co-infection with tick-borne relapsing fever in Dakar

BACKGROUND

West African tick-borne relapsing fever (TBRF) due to Borrelia crocidurae and malaria are co-endemics in Senegal. Although expected to be high, co-infections are rarely reported. A case of falciparum malaria and B. crocidurae co-infection in a patient from Velingara (South of Senegal) is discussed.

CASE

A 28 year-old-male patient presented to Aristide Le Dantec Hospital for recurrent fever. He initially presented to a local post health of Pikine (sub-urban of Dakar) and was diagnosed for malaria on the basis of positive malaria rapid diagnostic test (RDT) specific to Plamodium falciparum. The patient was treated as uncomplicated falciparum malaria. Four days after admission the patient was referred to Le Dantec Hospital. He presented with fever (39 °C), soreness, headache and vomiting. The blood pressure was 120/80 mmHg. The rest of the examination was normal. A thick film from peripheral blood was performed and addressed to the parasitology laboratory of the hospital. Thick film was stained with 10% Giemsa. Trophozoite of P. falciparum was identified at parasite density of 47 parasites per microlitre. The presence of Borrelia was also observed, concluding to malaria co-infection with borreliosis.

CONCLUSIONS

Signs of malaria can overlap with signs of borreliosis leading to the misdiagnosis of the latter. Thick and thin smear or QBC test or molecular method may be helpful to detect both Plamodium species and Borrelia. In addition, there is a real need to consider co-infections with other endemics pathogens when diagnosing malaria.

Head Lice of Pygmies Reveal the Presence of Relapsing Fever Borreliae in the Republic of Congo

BACKGROUND

Head lice, Pediculus humanus capitis, occur in four divergent mitochondrial clades (A, B, C and D), each having particular geographical distributions. Recent studies suggest that head lice, as is the case of body lice, can act as a vector for louse-borne diseases. Therefore, understanding the genetic diversity of lice worldwide is of critical importance to our understanding of the risk of louse-borne diseases.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we report the results of the first molecular screening of pygmies' head lice in the Republic of Congo for seven pathogens and an analysis of lice mitochondrial clades. We developed two duplex clade-specific real-time PCRs and identified three major mitochondrial clades: A, C, and D indicating high diversity among the head lice studied. We identified the presence of a dangerous human pathogen, Borrelia recurrentis, the causative agent of relapsing fever, in ten clade A head lice, which was not reported in the Republic of Congo, and B. theileri in one head louse. The results also show widespread infection among head lice with several species of Acinetobacter. A. junii was the most prevalent, followed by A. ursingii, A. baumannii, A. johnsonii, A. schindleri, A. lwoffii, A. nosocomialis and A. towneri.

CONCLUSIONS/SIGNIFICANCE

Our study is the first to show the presence of B. recurrentis in African pygmies' head lice in the Republic of Congo. This study is also the first to report the presence of DNAs of B. theileri and several species of Acinetobacter in human head lice. Further studies are needed to determine whether the head lice can transmit these pathogenic bacteria from person to another.

Molecular Evidence of Malaria and Zoonotic Diseases Among Rapid Diagnostic Test-Negative Febrile Patients in Low-Transmission Season, Mali

From November to December 2012 in Sélingué-Mali, blood samples from 88 febrile patients who tested negative by malaria Paracheck^® rapid diagnostic tests (RDTs) were used to assess the presence of sub-RDT Plasmodium falciparum as well as Borrelia, Coxiella burnetii, and Babesia applying molecular tools. Plasmodium sp. was present among 57 (60.2%) of the 88 malaria RDT-negative patients, whereas the prevalence of Borrelia, C. burnetii, and Babesia were 3.4% (N = 3), 1.1% (N = 1), and 0.0%, respectively. The additional diagnostic use of polymerase chain reaction (PCR) identified a high proportion of Plasmodium sp.-positive samples and although this may be a concern for malaria control, the respective PCR-identified malaria infections were less likely responsible for the observed fevers given the low parasite density. Also, the low infection levels of Borrelia and C. burnetii and lack of Babesia among the febrile patients call for further studies to assess the causes of fever among malaria RDT-negative patients in Sélingué.

An Alternative Strategy of Preventive Control of Tick-Borne Relapsing Fever in Rural Areas of Sine-Saloum, Senegal

In Senegal, tick-borne relapsing fever (TBRF) is a major cause of morbidity and a neglected public health problem. Borreliosis cases commonly detected in two villages led us to implement a borreliosis preventive control including cementing of floors in bedrooms and outbuildings attended by inhabitants to avoid human contacts with tick vectors. Epidemiological and medical monitoring of the TBRF incidence was carried out at Dielmo and Ndiop by testing the blood of febrile patients since 1990 and 1993, respectively. Intra-domiciliary habitat conditions were improved by cementing, coupled with accompanying measures, from March 2013 to September 2015. Application of this strategy was associated with a significant reduction of borreliosis incidence. This was more evident in Dielmo, dropping from 10.55 to 2.63 cases per 100 person-years (P < 0.001), than in Ndiop where it changed from 3.79 to 1.39 cases per 100 person-years (P < 0.001). Thirty-six cases of TBRF were estimated to be prevented at a cost of €526 per infection. The preventive control strategy was successful in Dielmo and Ndiop, being associated with decreased incidence by 89.8% and 81.5%, respectively, suggesting that TBRF may be widely decreased when the population is involved. Public health authorities or any development stakeholders should adopt this effective tool for promoting rural health through national prevention programs.

Novel Borrelia species detected in echidna ticks, Bothriocroton concolor, in Australia

BACKGROUND

To date, little has been documented about microorganisms harboured within Australian native ticks or their pathogenic potential. Recently, a Borrelia sp. related to the Relapsing Fever (RF) group was identified in a single tick removed from a wild echidna (Tachyglossus aculeatus). The present study investigated the presence of Borrelia in 97 Bothriocroton concolor ticks parasitizing echidnas in Queensland, New South Wales, and Victoria, Australia, using nested PCR with Borrelia-specific primers targeting the 16S rRNA (16S) and flaB genes.

RESULTS

Borrelia-specific PCR assays confirmed the presence of a novel Borrelia sp. related to the RF and reptile-associated (REP) spirochaetes in 38 (39 %) B. concolor ticks. This novel Borrelia sp. was identified in 41 % of the B. concolor ticks in Queensland and New South Wales, but not in any ticks from Victoria. The resulting flaB sequences (407 bp) were 88 and 86 % similar to the flaB sequences from Borrelia turcica and Borrelia hermsii, respectively. Of the ticks confirmed as Borrelia-positive following the flaB assay, 28 were positive with the 16S assay. Phylogenetic analysis of the 16S sequences (1097 bp) suggests that these sequences belong to a novel Borrelia sp., which forms a unique monophyletic clade that is similar to, but distinct from, RF Borrelia spp. and REP-associated Borrelia spp.

CONCLUSIONS

We conclude that the novel Borrelia sp. identified in this study does not belong to the Borrelia burgdorferi (sensu lato) complex, and that the phylogenetic analysis of the partial 16S gene sequences suggests it forms a unique monophyletic cluster in the genus Borrelia, potentially forming a fourth major group in this genus associated with monotremes in Australia. However, a thorough molecular characterisation will be required to confirm the phylogenetic position of this unique Borrelia sp. The zoonotic potential and pathogenic consequences of this novel Borrelia sp. are unknown at the current time.

Borrelia crocidurae infection in acutely febrile patients, Senegal

As malaria cases in Africa decline, other causes of acute febrile illness are being explored. To determine incidence of Borrelia crocidurae infection during June 2010–October 2011, we collected 1,566 blood specimens from febrile patients in Senegal. Incidence was high (7.3%). New treatment strategies, possibly doxycycline, might be indicated for febrile patients.

Multiple Pathogens Including Potential New Species in Tick Vectors in Côte d'Ivoire

BACKGROUND

Our study aimed to assess the presence of different pathogens in ticks collected in two regions in Côte d'Ivoire.

METHODOLOGY/PRINCIPAL FINDINGS

Real-time PCR and standard PCR assays coupled to sequencing were used. Three hundred and seventy eight (378) ticks (170 Amblyomma variegatum, 161 Rhipicepalus microplus, 3 Rhipicephalus senegalensis, 27 Hyalomma truncatum, 16 Hyalomma marginatum rufipes, and 1 Hyalomma impressum) were identified and analyzed. We identified as pathogenic bacteria, Rickettsia africae in Am. variegatum (90%), Rh. microplus (10%) and Hyalomma spp. (9%), Rickettsia aeschlimannii in Hyalomma spp. (23%), Rickettsia massiliae in Rh. senegalensis (33%) as well as Coxiella burnetii in 0.2%, Borrelia sp. in 0.2%, Anaplasma centrale in 0.2%, Anaplasma marginale in 0.5%, and Ehrlichia ruminantium in 0.5% of all ticks. Potential new species of Borrelia, Anaplasma, and Wolbachia were detected. Candidatus Borrelia africana and Candidatus Borrelia ivorensis (detected in three ticks) are phylogenetically distant from both the relapsing fever group and Lyme disease group borreliae; both were detected in Am. variegatum. Four new genotypes of bacteria from the Anaplasmataceae family were identified, namely Candidatus Anaplasma ivorensis (detected in three ticks), Candidatus Ehrlichia urmitei (in nine ticks), Candidatus Ehrlichia rustica (in four ticks), and Candidatus Wolbachia ivorensis (in one tick).

CONCLUSIONS/SIGNIFICANCE

For the first time, we demonstrate the presence of different pathogens such as R. aeschlimannii, C. burnetii, Borrelia sp., A. centrale, A. marginale, and E. ruminantium in ticks in Côte d'Ivoire as well as potential new species of unknown pathogenicity.

Borrelia infection in small mammals in West Africa and its relationship with tick occurrence inside burrows

Tick-borne relapsing fever (TBRF) is a zoonotic disease caused by several Borrelia species transmitted to humans by Ornithodoros tick vectors. In West Africa, Borrelia crocidurae is a common cause of disease in many rural populations. Small mammals act as reservoirs of infection. We report here the results of surveys that investigated the occurrence of B. crocidurae infection in rodents and insectivores from eight countries of West and Central Africa. Animals were identified at the species level and tested for Borrelia either by examination of thick blood film, intra-peritoneal inoculation of blood or brain tissues into laboratory mice, or by molecular techniques. A total of 4358 small mammals belonging to 38 species and 7 families were collected, including 3225 specimens collected in areas where the occurrence of Ornithodoros sonrai tick in rodent burrows was documented, and 1133 in areas where this tick was absent. In areas with O. sonrai, Borrelia infection was demonstrated in 287 of 3109 (9.2%) small mammals tested, and none was documented in 1004 animals tested from other areas. There was no relationship between the occurrence of Rhipicephalus, Hyaloma and Argas ticks in burrows and the distribution of Borrelia infection in small mammals. The 287 specimens infected by Borrelia belonged to 15 rodent and shrew species, including three Saharo-Sahelian species - Gerbillus gerbillus, Gerbillus occiduus and Gerbillus tarabuli - identified as reservoirs for TBRF with a distribution restricted to this area. In Sudan and Sudano-Sahelian areas, Arvicanthis niloticus, Mastomys erythroleucus and Mastomys huberti were the main reservoir of infection. Although most small mammals species collected had a large distribution in West and Central Africa, the fact that only animals collected in areas with O. sonrai were found infected suggest that this tick is the only vector of TBRF in rodents and insectivores in this part of Africa.

Monoclonal Antibodies for the Diagnosis of Borrelia crocidurae

Relapsing fever borreliae, produced by ectoparasite-borne Borrelia species, cause mild to deadly bacteremia and miscarriage. In the perspective of developing inexpensive assays for the rapid detection of relapsing fever borreliae, we produced 12 monoclonal antibodies (MAbs) against Borrelia crocidurae and characterized the two exhibiting the highest titers. P3A10 MAb reacts with the 35.6-kDa flagellin B (flaB) of B. crocidurae while P6D9 MAb recognizes a 35.1-kDa variable-like protein (Vlp) in B. crocidurae and a 35.2-kDa Vlp in Borrelia duttonii. Indirect immunofluorescence assay incorporating relapsing fever and Lyme group borreliae and 11 blood-borne organisms responsible for fever in West Africa confirmed the reactivity of these two MAbs. Combining these two MAbs in indirect immunofluorescence assays detected relapsing fever borreliae including B. crocidurae in ticks and the blood of febrile Senegalese patients. Both antibodies could be incorporated into inexpensive and stable formats suited for the rapid point-of-care diagnosis of relapsing fever. These first-ever MAbs directed against African relapsing fever borreliae are available for the scientific community to promote research in this neglected field.

Laboratory Diagnosis of Tick-Borne African Relapsing Fevers: Latest Developments

In Africa, relapsing fevers caused by ectoparasite-borne Borrelia species are transmitted by ticks, with the exception of Borrelia recurrentis, which is a louse-borne spirochete. These tropical diseases are responsible for mild to deadly spirochetemia. Cultured Borrelia crocidurae, Borrelia duttonii, and Borrelia hispanica circulate alongside at least six species that have not yet been cultured in vectors. Direct diagnosis is hindered by the use of non-specific laboratory tools. Indeed, microscopic observation of Borrelia spirochaeta in smears of peripheral blood taken from febrile patients lacks sensitivity and specificity. Although best visualized using dark-field microscopy, the organisms can also be detected using Wright–Giemsa or acridine orange stains. PCR-based detection of specific sequences in total DNA extracted from a specimen can be used to discriminate different relapsing fever Borreliae. In our laboratory, we developed a multiplex real-time PCR assay for the specific detection of B. duttonii/recurrentis and B. crocidurae: multispacer sequence typing accurately identified cultured relapsing fever borreliae and revealed diversity among them. Other molecular typing techniques, such as multilocus sequence analysis of tick-borne relapsing fever borreliae, showed the potential risk of human infection in Africa. Recent efforts to culture and sequence relapsing fever borreliae have provided new information for reassessment of the diversity of these bacteria. Recently, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry has been reported as a means of identifying cultured borreliae and of identifying both vectors and vectorized pathogens such as detecting relapsing fever borreliae directly in ticks. The lack of a rapid diagnosis test restricts the management of such diseases. We produced monoclonal antibodies against B. crocidurae in order to develop cheap assays for the rapid detection of relapsing fever borreliae. In this paper, we review point-of-care diagnosis and confirmatory methods.