A novel animal model of Borrelia recurrentis louse-borne relapsing fever borreliosis using immunodeficient mice

Prevalence of Lyme Disease and Relapsing Fever Borrelia spp. in Vectors, Animals, and Humans within a One Health Approach in Mediterranean Countries

The genus Borrelia has been divided into Borreliella spp., which can cause Lyme Disease (LD), and Borrelia spp., which can cause Relapsing Fever (RF). The distribution of genus Borrelia has broadened due to factors such as climate change, alterations in land use, and enhanced human and animal mobility. Consequently, there is an increasing necessity for a One Health strategy to identify the key components in the Borrelia transmission cycle by monitoring the human-animal-environment interactions. The aim of this study is to summarize all accessible data to increase our understanding and provide a comprehensive overview of Borrelia distribution in the Mediterranean region. Databases including PubMed, Google Scholar, and Google were searched to determine the presence of Borreliella and Borrelia spp. in vectors, animals, and humans in countries around the Mediterranean Sea. A total of 3026 were identified and screened and after exclusion of papers that did not fulfill the including criteria, 429 were used. After examination of the available literature, it was revealed that various species associated with LD and RF are prevalent in vectors, animals, and humans in Mediterranean countries and should be monitored in order to effectively manage and prevent potential infections.

Male C57BL/6J mice have higher presence and abundance of Borrelia burgdorferi in their ventral skin compared to female mice

Borrelia burgdorferi is a tick-borne spirochete that causes Lyme disease in humans. The host immune system controls the abundance of the spirochete in the host tissues. Recent work with immunocompetent Mus musculus mice strain C3H/HeJ found that males had a higher tissue infection prevalence and spirochete load compared to females. The purpose of this study was to determine whether host sex and acquired immunity interact to influence the prevalence and abundance of spirochetes in the tissues of the commonly used mouse strain C57BL/6. Wildtype (WT) mice and their SCID counterparts (C57BL/6) were experimentally infected with B. burgdorferi via tick bite. Ear biopsies were sampled at weeks 4, 8, and 12 post-infection (PI) and five tissues (left ear, ventral skin, heart, tibiotarsal joint of left hind leg, and liver) were collected at necropsy (16 weeks PI). The mean spirochete load in the tissues of the SCID mice was 260.4x higher compared to the WT mice. In WT mice, the infection prevalence in the ventral skin was significantly higher in males (40.0 %) compared to females (0.0 %), and the spirochete load in the rear tibiotarsal joint was significantly higher (4.3x) in males compared to females. In SCID mice, the spirochete load in the ventral skin was 200.0x higher in males compared to females, but there were no significant sex-specific difference in spirochete load in the other tissues (left ear, heart, tibiotarsal joint, or liver). Thus, the absence of acquired immunity greatly amplified the spirochete load in the ventral skin of male mice. It is important to note that the observed sex-specific differences in laboratory mice cannot be extrapolated to humans. Future studies should investigate the mechanisms underlying the male bias in the abundance of B. burgdorferi in the mouse skin.

Early Transcriptional Changes in the Midgut of Ornithodoros moubata after Feeding and Infection with Borrelia duttonii

Studies on tick-pathogen-host interactions are helping to identify candidates for vaccines against ticks and tick-borne diseases and to discover potent bioactive tick molecules. The tick midgut is the main tissue involved in blood feeding and, moreover, the first organ to have contact with pathogens ingested through the blood meal. As little is known about the molecular biology of feeding and tick defence mechanisms against microorganisms, but important for understanding vector-pathogen interactions, we explored the early transcriptional changes in the midgut of Ornithodoros moubata after feeding and in response to challenge with the relapsing-fever spirochete Borrelia duttonii using the Ion S5XL platform. Besides transcripts with metabolic function and immune-related transcripts we discovered numerous putative and uncharacterized protein sequences. Overall, our analyses support previous studies and provides a valuable reference database for further functional proteomic analysis of midgut proteins of O. moubata.

The First Immunocompetent Mouse Model of Strictly Human Pathogen, Borrelia recurrentis

The spirochetal bacterium Borrelia recurrentis causes louse-borne relapsing fever (LBRF). B. recurrentis is unique because, as opposed to other Borrelia spirochetes, this strictly human pathogen is transmitted by lice. Despite the high mortality and historically proven epidemic potential and current outbreaks in African countries and Western Europe, research on LBRF has been obstructed by the lack of suitable animal models. The previously used grivet monkey model is associated with ethical concerns, among other issues. An existing immunodeficient mouse model does not limit bacteremia due to its impaired immune system. In this study, we used genetically diverse Collaborative Cross (CC) lines to develop the first LBRF immunocompetent mouse model. Out of 12 CC lines tested, CC046 mice consistently developed B. recurrentis-induced spirochetemia during the first 3 days postchallenge as concordantly detected by dark-field microscopy, culture, and quantitative PCR. However, spirochetemia was not detected from day 4 through day 10 postchallenge. The high-level spirochetemia (>10⁷ cells/ml of blood) observed in CC046 mice was similar to that recorded in LBRF patients as well as immunocompetent mouse strains experimentally infected by tick-borne relapsing fever (RF) spirochetes, Borrelia hermsii and Borrelia persica. In contrast to the Old World and New World RF spirochetes, which develop multiple relapses (n = 3 to 9), B. recurrentis produced only single culture-detectable spirochetemia in CC046 mice. The lack of relapses may not be surprising, as LBRF patients and the grivet monkey model usually develop no or only 1 to 2 spirochetemic relapses. The novel model will now allow scientists to study B. recurrentis in the context of intact immunity.

Louse-borne relapsing fever-A systematic review and analysis of the literature: Part 1-Epidemiology and diagnostic aspects

Louse-borne relapsing fever (LBRF) is a classical epidemic disease, which in the past was associated with war, famine, poverty, forced migration, and crowding under poor hygienic conditions around the world. The disease's causative pathogen, the spirochete bacterium Borrelia recurrentis, is confined to humans and transmitted by a single vector, the human body louse Pediculus humanus. Since the disease has had its heyday before the days of modern medicine, many of its aspects have never been formally studied and to date, remain incompletely understood. In order to shed light on some of these aspects, we have systematically reviewed the accessible literature on LBRF, since the recognition of its mode of transmission in 1907, and summarized the existing data on epidemiology and diagnostic 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 LBRF published in English, French, German, and Spanish since 1907 were included. Data extraction followed a predefined protocol and included a grading system to judge the certainty of the diagnosis of reported cases. Historically, Ethiopia is considered a stronghold of LBRF. The recognition of LBRF among East African migrants (originating from Somalia, Eritrea, and Ethiopia) arriving to Europe in the course of the recent migration flow from this region suggests that this epidemiological focus ostensibly persists. Currently, there is neither evidence to support or refute active transmission foci of LBRF elsewhere on the African continent, in Latin America, or in Asia. Microscopy remains the most commonly used method to diagnose LBRF. Data are lacking on sensitivity and specificity of most diagnostic methods.

Pathogenesis of Relapsing Fever

Relapsing fever (RF) is caused by several species of Borrelia; all, except two species, are transmitted to humans by soft (argasid) ticks. The species B. recurrentis is transmitted from one human to another by the body louse, while B. miyamotoi is vectored by hard-bodied ixodid tick species. RF Borrelia have several pathogenic features that facilitate invasion and dissemination in the infected host. In this article we discuss the dynamics of vector acquisition and subsequent transmission of RF Borrelia to their vertebrate hosts. We also review taxonomic challenges for RF Borrelia as new species have been isolated throughout the globe. Moreover, aspects of pathogenesis including symptomology, neurotropism, erythrocyte and platelet adhesion are discussed. We expound on RF Borrelia evasion strategies for innate and adaptive immunity, focusing on the most fundamental pathogenetic attributes, multiphasic antigenic variation. Lastly, we review new and emerging species of RF Borrelia and discuss future directions for this global disease.

Louse-borne relapsing fever (Borrelia recurrentis infection)

Louse-borne relapsing fever (LBRF) is an epidemic disease with a fascinating history from Hippocrates’ times, through the 6th century ‘Yellow Plague’, to epidemics in Ireland, Scotland and England in the 19th century and two large Afro-Middle Eastern pandemics in the 20th century. An endemic focus persists in Ethiopia and adjacent territories in the Horn of Africa. Since 2015, awareness of LBRF in Europe, as a re-emerging disease, has been increased dramatically by the discovery of this infection in dozens of refugees arriving from Africa.

The causative spirochaete, Borrelia recurrentis, has a genome so similar to B. duttonii and B. crocidurae (causes of East and West African tick-borne relapsing fever), that they are now regarded as merely ecotypes of a single genomospecies. Transmission is confined to the human body louse Pediculus humanus corporis, and, perhaps, the head louse P. humanus capitis, although the latter has not been proved. Infection is by inoculation of louse coelomic fluid or faeces by scratching. Nosocomial infections are possible from contamination by infected blood. Between blood meals, body lice live in clothing until the host's body temperature rises or falls, when they seek a new abode.

The most distinctive feature of LBRF, the relapse phenomenon, is attributable to antigenic variation of borrelial outer-membrane lipoprotein. High fever, rigors, headache, pain and prostration start abruptly, 2–18 days after infection. Petechial rash, epistaxis, jaundice, hepatosplenomegaly and liver dysfunction are common. Severe features include hyperpyrexia, shock, myocarditis causing acute pulmonary oedema, acute respiratory distress syndrome, cerebral or gastrointestinal bleeding, ruptured spleen, hepatic failure, Jarisch–Herxheimer reactions (J-HR) and opportunistic typhoid or other complicating bacterial infections. Pregnant women are at high risk of aborting and perinatal mortality is high.

Rapid diagnosis is by microscopy of blood films, but polymerase chain reaction is used increasingly for species diagnosis. Severe falciparum malaria and leptospirosis are urgent differential diagnoses in residents and travellers from appropriate geographical regions.

High untreated case-fatality, exceeding 40% in some historic epidemics, can be reduced to less than 5% by antibiotic treatment, but elimination of spirochaetaemia is often accompanied by a severe J-HR.

Epidemics are controlled by sterilising clothing to eliminate lice, using pediculicides and by improving personal hygiene.

Macrophages and Galectin 3 Control Bacterial Burden in Acute and Subacute Murine Leptospirosis That Determines Chronic Kidney Fibrosis

Previous studies have suggested that macrophages may contribute to acute Leptospira dissemination, as well as having a major role in kidney fibrosis. Our aim was to characterize the role of macrophages and galectin 3 (Gal-3) on the survival, clinical course, bacterial burden, interstitial nephritis, and chronic kidney fibrosis in Leptospira interrogans serovar Copenhageni (LIC)-induced experimental murine leptospirosis. C57BL/6J mice depleted of macrophages by liposome-encapsulated clodronate treatment and infected with LIC presented a higher bacterial burden, had reduced subacute nephritis and enhanced chronic kidney fibrosis relative to untreated, infected mice. Moreover, LIC infection in mice whose Gal-3 was disrupted (Lgals3^−/–) had a higher bacterial burden and enhanced subacute nephritis and chronic kidney fibrosis when compared to C57BL/6J wild-type mice. Chronic fibrosis did not correlate with higher transcription levels of TGF-β1 or IL-13 in the kidneys. Kidney fibrosis was found in chronically infected rats as well as in wild infected rats. On the other hand, human fibroblast cultures exhibited enhanced differentiation to myofibroblasts after treatment with LIC. Our results demonstrate that macrophages and Gal-3 play a critical role in controlling the LIC burden but has a minor role in subsequent fibrosis. Instead, kidney fibrosis was better correlated with bacterial burden. Taken together, our results do not support a role for macrophages to disseminate leptospires during acute infection, nor in chronic kidney fibrosis.

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.

First insights in the variability of Borrelia recurrentis genomes

Background

Borrelia recurrentis is the causative agent of louse-borne relapsing fever, endemic to the Horn of Africa. New attention was raised in Europe, with the highest number of cases (n = 45) reported among migrants in 2015 in Germany and sporadically from other European countries. So far only one genome was sequenced, hindering the development of specific molecular diagnostic and typing tools. Here we report on modified culture conditions for B. recurrentis and the intraspecies genome variability of six isolates isolated and cultured in different years in order to explore the possibility to identify new targets for typing and examine the molecular epidemiology of the pathogen.

Methodology/Principal findings

Two historical isolates from Ethiopia and four isolates from migrants from Somalia (n = 3) and Ethiopia (n = 1) obtained in 2015 were cultured in MPK-medium supplemented with 50% foetal calf serum. Whole DNA was sequenced using Illumina MiSeq technology and analysed using the CLC Genomics Workbench and SPAdes de novo assembler. Compared to the reference B. recurrentis A1 29–38 SNPs were identified in the genome distributed on the chromosome and plasmids. In addition to that, plasmids of differing length, compared to the available reference genome were identified.

Conclusions/Significance

The observed low genetic variability of B. recurrentis isolates is possibly due to the adaptation to a very conserved vector-host (louse-human) cycle, or influenced by the fastidious nature of the pathogen and their resistance to in vitro growth. Nevertheless, isolates obtained in 2015 were bearing the same chromosomal SNPs and could be distinguished from the historical isolates by means of whole genome sequencing, but not hitherto used typing methods. This is the first study examining the molecular epidemiology of B. recurrentis and provides the necessary background for the development of better diagnostic tools.

Louse-borne relapsing fever, as the name suggests, is the only relapsing fever transmitted by lice, and caused by the spirochaete Borrelia recurrentis. Today it is endemic to the Horn of Africa, but due to the cosmopolitan nature of the vector, the pathogen still bears epidemic potential to spread globally among vulnerable populations. The most recent account of that has been observed among migrants arriving to Europe in 2015. Up to date, only one strain was sequenced, thus hampering the development of species-specific typing tools. We employed state-of-the-art high-throughput sequencing to six B. recurrentis isolates obtained at different time-points and currently available in culture. Our aim was to address the question of genome variability of this pathogen at the highest resolution and provide information necessary for the development of specific typing tools. B. recurrentis has highly conserved genomes, differing in 29–38 SNPs compared to the reference genome B. recurrentis A1, all identified outside the loci currently developed and used for relapsing fever Borrelia typing. Therefore, applying these typing methods would render them indistinguishable, while at the SNP level we found a distinction between isolates obtained in 2015 from migrants and the two historical isolates. Our data provide first insights in the genome variability and baseline information necessary for further studies of the molecular epidemiology of the pathogen and for the development of improved diagnostic tools.

[Relapsing (recurrent) disease caused by Borrelia miyamotoi]

AIM

To clarify the clinical, laboratory, and epidemiological characteristics of relapsing Ixodes tick-borne borreliosis (ITB) caused by Borrelia miyamotoi.

SUBJECTS AND METHODS

Retrospective clinical observation was made in 79 inpatients of the Republican Infectious Diseases Hospital (Udmurt Republic), who had been diagnosed with B. miyamotoi-caused disease verified by real-time polymerase chain reaction. The latter and enzyme immunoassay ruled out possible vector-borne coinfections (ITB caused by B. burgdorferi sensu lato; tick-borne encephalitis; anaplasmosis; and ehrlichiosis).

RESULTS

The recurrent course of the disease was observed in 8 (10%) of the 79 patients. The relapsing fever curve was noted in 6 of the 8 patients; 4 patients had 2 episodes of fever and 2 patients had 3 episodes; the wave-like continuous type of fever cannot enable one to estimate the specific number of episodes in 2 more cases. Relapses occurred in all the 8 patients before antibiotic treatment. Febrile syndrome (weakness, headache, chill, fever, sweating, dizziness, nausea, vomiting, myalgia, and arthralgia) was leading in patients with relapses. These patients were less frequently observed to have signs of organ dysfunctions than those with one episode of fever. The values of clinical and biochemical blood tests and urinalyses were normal and near-normal in the majority of patients on hospital admission.

CONCLUSION

Relapsing B. miyamotoi infection cases detected in the directed study proved to be unrecognized by practical health authorities during the first and sometimes second episodes of fever. This indicates that the prevalence of this disease is essentially underestimated and there is a need to increase physicians' alertness and awareness and to introduce adequate diagnostic methods.

Borrelia persica Infection in Immunocompetent Mice--A New Tool to Study the Infection Kinetics In Vivo

Borrelia persica, a bacterium transmitted by the soft tick Ornithodoros tholozani, causes tick-borne relapsing fever in humans in the Middle East, Central Asia and the Indian peninsula. Immunocompetent C3H/HeOuJ mice were infected intradermally with B. persica at varying doses: 1 x 10⁶, 1 x 10⁴, 1 x 10² and 4 x 10⁰ spirochetes/mouse. Subsequently, blood samples were collected and screened for the presence of B. persica DNA. Spirochetes were detected in all mice infected with 1 x 10⁶, 1 x 10⁴ and 1 x 10² borrelia by real-time PCR targeting the flaB gene of the bacterium. Spirochetemia developed with a one- to two-day delay when 1 x 10⁴ and 1 x 10² borrelia were inoculated. Mice injected with only four organisms were negative in all tests. No clinical signs were observed when infected mice were compared to negative control animals. Organs (heart, spleen, urinary bladder, tarsal joint, skin and brain) were tested for B. persica-specific DNA and cultured for the detection of viable spirochetes. Compiled data show that the target organs of B. persica infections are the brain and the skin. A newly developed serological two-tiered test system (ELISA and western blot) for the detection of murine IgM, IgG and IgA antibody titers against B. persica showed a vigorous antibody response of the mice during infection. In conclusion, the infection model described here for B. persica is a platform for in vivo studies to decipher the so far unexplored survival strategies of this Borrelia species.

The spirochete Borrelia persica is a tick-borne bacterium that is transmitted by the vector Ornithodoros tholozani to its vertebrate host in the Middle East, Central Asia and the Indian peninsula. Current migration of vast numbers of individuals from this area increases the likelihood that B. persica infections will be introduced into new geographic regions. After infection and distribution by the bloodstream, relapsing fever episodes occur in humans. Since no reliable in vivo tools have existed so far to study this organism, a murine model was established in this study to characterize the infection kinetics in immunocompetent mice. Aspects of the potential infectivity of the laboratory strain and of potential clinical signs, spirochetemia and antibody response as well as organ tropism and histopathological reactions were studied. With the successful infection model presented here, further studies are conceivable in order to gain advanced insights into the pathogenesis of B. persica infection and to characterize in detail the host immune response mounted against the bacterium. We propose that this model could also be used for the development of new rapid diagnostic approaches to initiate or monitor treatment regimes in order to clear or prevent the infection with B. persica.

Relapsing Fever Borreliae: A Global Review

Relapsing fever borreliae were notorious and feared infectious agents that earned their place in history through their devastating impact as causes of both epidemic and endemic infection. They are now considered more as an oddity, and their burden of infection is largely overshadowed by other infections such as malaria, which presents in a similar clinical way. Despite this, they remain the most common bacterial infection in some developing countries. Transmitted by soft ticks or lice, these fascinating spirochetes have evolved a myriad of mechanisms to survive within their diverse environments.

Maladjusted host immune responses induce experimental cerebral malaria-like pathology in a murine Borrelia and Plasmodium co-infection model

In the Plasmodium infected host, a balance between pro- and anti-inflammatory responses is required to clear the parasites without inducing major host pathology. Clinical reports suggest that bacterial infection in conjunction with malaria aggravates disease and raises both mortality and morbidity in these patients. In this study, we investigated the immune responses in BALB/c mice, co-infected with Plasmodium berghei NK65 parasites and the relapsing fever bacterium Borrelia duttonii. In contrast to single infections, we identified in the co-infected mice a reduction of L-Arginine levels in the serum. It indicated diminished bioavailability of NO, which argued for a dysfunctional endothelium. Consistent with this, we observed increased sequestration of CD8+ cells in the brain as well over expression of ICAM-1 and VCAM by brain endothelial cells. Co-infected mice further showed an increased inflammatory response through IL-1β and TNF-α, as well as inability to down regulate the same through IL-10. In addition we found loss of synchronicity of pro- and anti-inflammatory signals seen in dendritic cells and macrophages, as well as increased numbers of regulatory T-cells. Our study shows that a situation mimicking experimental cerebral malaria (ECM) is induced in co-infected mice due to loss of timing and control over regulatory mechanisms in antigen presenting cells.

Human complement regulators C4b-binding protein and C1 esterase inhibitor interact with a novel outer surface protein of Borrelia recurrentis

The spirochete Borrelia recurrentis is the causal agent of louse-borne relapsing fever and is transmitted to humans by the infected body louse Pediculus humanus. We have recently demonstrated that the B. recurrentis surface receptor, HcpA, specifically binds factor H, the regulator of the alternative pathway of complement activation, thereby inhibiting complement mediated bacteriolysis. Here, we show that B. recurrentis spirochetes express another potential outer membrane lipoprotein, termed CihC, and acquire C4b-binding protein (C4bp) and human C1 esterase inhibitor (C1-Inh), the major inhibitors of the classical and lectin pathway of complement activation. A highly homologous receptor for C4bp was also found in the African tick-borne relapsing fever spirochete B. duttonii. Upon its binding to B. recurrentis or recombinant CihC, C4bp retains its functional potential, i.e. facilitating the factor I-mediated degradation of C4b. The additional finding that ectopic expression of CihC in serum sensitive B. burgdorferi significantly increased spirochetal resistance against human complement suggests this receptor to substantially contribute, together with other known strategies, to immune evasion of B. recurrentis.

Borrelia recurrentis, the causal agent of louse-borne relapsing fever is transmitted to humans via infected body lice. Infection with B. recurrentis has been achieved only in humans and is accompanied by a systemic inflammatory disease, multiple relapses of fever and massive spirochetemia. A key virulence factor of B. recurrentis is their potential to undergo antigenic variation. However, for survival in the blood during the early phase of infection and for persistence in human tissues, spirochetes must be endowed with robust tools to escape innate immunity. We have recently shown that B. recurrentis acquires the serum-derived regulator factor H, thereby blocking the alternative complement pathway. Here, we show that B. recurrentis expresses in addition a novel outer surface lipoprotein that selectively binds serum-derived C4b-binding protein and C1 esterase inhibitor, two endogenous regulators of the classical and lectin pathway of complement activation. The combined data underscore the versatility of B. recurrentis to effectively evade innate and adaptive immunity, including serum resistance. Thus, the present study elucidates a new mechanism of B. recurrentis important for its evasion from complement attack and will be helpful for the development of new drugs against this fatal infection.