Influence of outer surface protein A antibody on Borrelia burgdorferi within feeding ticks

Intranasal vaccine for Lyme disease provides protection against tick transmitted Borrelia burgdorferi beyond one year

Strategies for disease control are necessary to reduce incidence of Lyme Disease (LD) including development of safe vaccines for human use. Parainfluenza virus 5 (PIV5) vector has an excellent safety record in animals and PIV5-vectored vaccines are currently under clinical development. We constructed PIV5-vectored LD vaccine candidates expressing OspA from B. burgdorferi (OspAB31) and a chimeric protein containing sequences from B. burgdorferi and B. afzelii (OspABPBPk). Immunogenicity and vaccine efficacy were analyzed in C3H-HeN mice after prime-boost intranasal vaccination with live PIV5-OspAB31 or PIV5-OspABPBPk, subcutaneous (s.c.) vaccination with rOspAB31+Alum, and the respective controls. Mice vaccinated intranasally with live PIV5-AB31 or PIV5-ABPBPk had higher endpoint titers of serum antibody against OspAB31 at 6- and 12- months post vaccination, compared to mice vaccinated s.c. with rOspAB31. Neutralization activity of antibody was maintained up to 18-months post-immunization, with the response greater in live PIV5-delivered OspA vaccines, than that induced by s.c. rOspAB31. Challenge with infected ticks carrying 10-19 strains of B. burgdorferi performed at 4-, 9- or 15-months post-immunization showed increased breakthrough infections in mice vaccinated with s.c. rOspAB31 compared to intranasal PIV5-AB31 or PIV5-ABPBPk at 9- and 15-months, as determined by quantification of serologic antibodies to B. burgdorferi proteins as well as flaB DNA in tissues, and by visualization of motile B. burgdorferi in culture of tissues under dark field microscope. These findings indicate that immunization of mice with PIV5 delivered OspA generates immune responses that produce longer-lasting protection ( > 1 year) against tick-transmitted B. burgdorferi than a parenteral recombinant OspA vaccine.

Agglutination of Borreliella burgdorferi by Transmission-Blocking OspA Monoclonal Antibodies and Monovalent Fab Fragments

Lyme disease vaccines based on recombinant Outer surface protein A (OspA) elicit protective antibodies that interfere with tick-to-host transmission of the disease-causing spirochete Borreliella burgdorferi. Another hallmark of OspA antisera and certain OspA monoclonal antibodies (MAbs) is their capacity to induce B. burgdorferi agglutination in vitro, a phenomenon first reported more than 30 years ago but never studied in molecular detail. In this report, we demonstrate that transmission-blocking OspA MAbs, individually and in combination, promote dose-dependent and epitope-specific agglutination of B. burgdorferi. Agglutination occurred within minutes and persisted for hours. Spirochetes in the core of the aggregates exhibited evidence of outer membrane (OM) stress, revealed by propidium iodide uptake. The most potent agglutinator was the mouse MAb LA-2, which targets the OspA C terminus (β-strands 18 to 20). Human MAb 319-44, which also targets the OspA C terminus (β-strand 20), and 857-2, which targets the OspA central β-sheet (strands 8 to 10), were less potent agglutinators, while MAb 221-7, which targets β-strands 10 to 11, had little to no measurable agglutinating activity, even though its affinity for OspA exceeded that of LA-2. Remarkably, monovalent Fab fragments derived from LA-2, and to a lesser degree 319-44, retained the capacity to induce B. burgdorferi aggregation and OM stress, a particularly intriguing observation considering that "LA-2-like" Fabs have been shown to experimentally entrap B. burgdorferi within infected ticks and prevent transmission during feeding to a mammalian host. It is therefore tempting to speculate that B. burgdorferi aggregation triggered by OspA-specific antibodies in vitro may in fact reflect an important biological activity in vivo.

The year that shaped the outcome of the OspA vaccine for human Lyme disease

The expansion of Lyme borreliosis endemic areas and the corresponding increase of disease incidence have opened the possibility for greater acceptance of a vaccine. In this perspective article, we discuss the discovery of outer surface protein A (OspA) of B. burgdorferi, and the subsequent pre-clinical testing and clinical trials of a recombinant OspA vaccine for human Lyme disease. We also discuss in detail the open public hearings of the FDA Lyme disease vaccine advisory panel held in 1998 where concerns of molecular mimicry induced autoimmunity to native OspA were raised, the limitations of those studies, and the current modifications of recombinant OspA to develop a multivalent subunit vaccine for Lyme disease.

A brief history of OspA vaccines including their impact on diagnostic testing for Lyme disease

The only United States Food and Drug Administration approved vaccine preparation to prevent Lyme disease consisted of a single recombinant outer surface protein A (OspA), which was marketed for use from late 1998 until early 2002, with no vaccine currently available for humans for nearly 20 years. OspA vaccines generate an antibody-mediated, transmission blocking immunity, that prevents Borrelia burgdorferi from being transmitted during a tick bite. Although this OspA vaccine was safe and effective, it likely would have required booster doses to maintain immunity, and vaccination regularly caused false positive results on first-tier serologic testing for Lyme disease, when a whole cell-based enzyme immunoassay was used. Clinical trials are in progress to test a new multivalent OspA vaccine designed to prevent Lyme disease in both the United States and Europe.

Maternal transfer of neutralizing antibodies to B. burgdorferi OspA after oral vaccination of the rodent reservoir

Lyme Disease presents unique challenges for public health. Transfer of protective antibodies between mothers and offspring should occur after vaccination of mice. We present new evidence for maternal transfer of oral vaccine induced neutralizing anti-OspA IgG antibodies to mouse pups mainly through ingestion of colostrum. We found a strong statistical correlation of antibody transfer between mothers that produced the most robust IgG response to OspA and their respective pups. OspA-specific antibody was detected as early as 24 h after birth and protective levels of antibodies lasted until ~5 weeks of age in the majority of pups but persisted in some mice until 9 weeks. This was further supported by detection of neutralizing antibodies in serum of all pups at 2-3 weeks after birth and in some offspring adult mice at 9 weeks of age. A clear association was found between robust antibody responses in mothers and the length of time antibody persisted in the respective pups using a novel longitudinal Bayesian model. These factors are likely to impact the enzootic cycle of B. burgdorferi if reservoir targeted OspA-based vaccination interventions are implemented.

Cross-kingdom analysis of nymphal-stage Ixodes scapularis microbial communities in relation to Borrelia burgdorferi infection and load

The tick microbiota may influence the colonization of Ixodes scapularis by Borrelia burgdorferi, the Lyme disease bacterium. Using conserved and pathogen-specific primers we performed a cross-kingdom analysis of bacterial, fungal, protistan and archaeal communities of I. scapularis nymphs (N = 105) collected from southern Vermont, USA. The bacterial community was dominated by a Rickettsia and several environmental taxa commonly reported in I. scapularis, as well as the human pathogens B. burgdorferi and Anaplasma phagocytophilum, agent of human granulocytic anaplasmosis. With the fungal primer set we detected primarily plant- and litter-associated taxa and >18% of sequences were Malassezia, a fungal genus associated with mammalian skin. Two 18S rRNA gene primer sets, intended to target protistan communities, returned mostly Ixodes DNA as well as the wildlife pathogen Babesia odocoilei (7% of samples), a Gregarines species (14%) and a Spirurida nematode (18%). Data from pathogen-specific and conserved primers were consistent in terms of prevalence and identification. We measured B. burgdorferi presence/absence and load and found that bacterial beta diversity varied based on B. burgdorferi presence/absence. Load was weakly associated with bacterial community composition. We identified taxa associated with B. burgdorferi infection that should be evaluated for their role in vector colonization by pathogens.

BBE31 from the Lyme disease agent Borrelia burgdorferi, known to play an important role in successful colonization of the mammalian host, shows the ability to bind glutathione

Lyme disease is a tick-borne infection caused by Borrelia burgdorferi sensu lato complex spirochetes. The spirochete is located in the gut of the tick; as the infected tick starts the blood meal, the spirochete must travel through the hemolymph to the salivary glands, where it can spread to and infect the new host organism. In this study, we determined the crystal structures of the key outer surface protein BBE31 from B. burgdorferi and its orthologous protein BSE31 (BSPA14S_RS05060 gene product) from B. spielmanii. BBE31 is known to be important for the transfer of B. burgdorferi from the gut to the hemolymph in the tick after a tick bite. While BBE31 exerts its function by interacting with the Ixodes scapularis tick gut protein TRE31, structural and mass spectrometry data revealed that BBE31 has a glutathione (GSH) covalently attached to Cys142 suggesting that the protein may have acquired some additional functions in contrast to its orthologous protein BSE31, which lacks any interactions with GSH. In the current study, in addition to analyzing the potential reasons for GSH binding, the three-dimensional structure of BBE31 provides new insights into the molecular details of the transmission process as the protein plays an important role in the initial phase before the spirochete is physically transferred to the new host. This knowledge will be potentially used for the development of new strategies to fight against Lyme disease.

Immunogenicity of the Lyme disease antigen OspA, particleized by cobalt porphyrin-phospholipid liposomes

Outer surface protein A (OspA) is a Borrelia lipoprotein and an established Lyme disease vaccine target. Admixing non-lipidated, recombinant B. burgdorferi OspA with liposomes containing cobalt porphyrin-phospholipid (CoPoP) resulted in rapid, particulate surface display of the conformationally intact antigen. Particleization was serum-stable and led to enhanced antigen uptake in murine macrophages in vitro. Mouse immunization using CoPoP liposomes that also contained a synthetic monophosphoryl lipid A (PHAD) elicited a Th1-biased OspA antibody response with higher IgG production compared to other vaccine adjuvants. Antibodies were reactive with intact B. burgdorferi spirochetes and Borrelia lysates, and induced complement-mediated borreliacidal activity in vitro. One year after initial immunization, mice maintained high levels of circulating borreliacidal antibodies capable of blocking B. burgdorferi transmission from infected ticks to human blood in a feeding chamber.

Antigen Engineering Approaches for Lyme Disease Vaccines

Increasing rates of Lyme disease necessitate preventive measures such as immunization to mitigate the risk of contracting the disease. At present, there is no human Lyme disease vaccine available on the market. Since the withdrawal of the first and only licensed Lyme disease vaccine based on lipidated recombinant OspA, vaccine and antigen research has aimed to overcome its risks and shortcomings. Replacement of the putative cross-reactive T-cell epitope in OspA via mutation or chimerism addresses the potential risk of autoimmunity. Multivalent approaches in Lyme disease vaccines have been pursued to address sequence heterogeneity of Lyme borreliae antigens and to induce a repertoire of functional antibodies necessary for efficient heterologous protection. This Review summarizes recent antigen engineering strategies that have paved the way for the development of next generation vaccines against Lyme disease, some of which have reached clinical testing. Bioconjugation methods that incorporate antigens to self-assembling nanoparticles for immune response potentiation are also discussed.

Diversity of the Lyme Disease Spirochetes and its Influence on Immune Responses to Infection and Vaccination

The Lyme disease spirochetes are a highly diverse group of bacteria with unique biological properties. Their ability to cycle between ticks and mammals requires that they adapt to variable and constantly changing environmental conditions. Outer surface protein C is an essential virulence determinant that has received considerable attention in vaccine and diagnostic assay development. Knowledge of OspC diversity, its antigenic determinants, and its production patterns throughout the enzootic cycle, as well as in the laboratory setting, is essential for understanding immune responses induced by infection or vaccination.

Treatment of Tick-Borne Diseases

OBJECTIVE:

To review the data regarding the pharmacotherapy of Lyme disease, Rocky Mountain spotted fever (RMSF), and the human ehrlichioses.

DATA SOURCES:

English-language literature was identified via MEDLINE (1966–January 2002) using the keywords Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis. Textbooks and other pertinent resources were also reviewed.

STUDY SELECTION AND DATA EXTRACTION:

All articles identified through the data sources above were evaluated and reviewed if pertinent to the objective.

DATA SYNTHESIS:

Tick-borne diseases are the most common vector-transmitted diseases in North America. Each disease causes significant morbidity and, in the case of RMSF, mortality if patients go untreated. If the disease syndromes are recognized early and treatment is initiated, complications are greatly reduced. Doxycycline is active against each of the causative organisms, simplifying empiric treatment.

CONCLUSIONS:

Effective pharmacotherapy exists to treat each of these diseases, assuming diagnosis is made quickly. The β-lactam and tetracycline antibiotics appear to be the most effective therapy for Lyme disease. The tetracyclines, but not the β-lactams, are effective for RMSF and the human ehrlichioses. Since Borrelia burgdorferi and the human granulocytic ehrlichiosis agent are becoming more common coinfecting pathogens, tetracycline or doxycycline should be considered the drugs of choice for patients from endemic areas where exposure to both pathogens may have occurred. Doxycycline is the preferred agent because of decreased frequency of administration and adverse effects.

BosR functions as a repressor of the ospAB operon in Borrelia burgdorferi

The Lyme disease spirochete, Borrelia burgdorferi, must abundantly produce outer surface lipoprotein A (OspA) in the tick vector but downregulate OspA in mammals in order to evade the immune system and maintain its natural enzootic cycle. Here, we show that BosR binds two regulatory elements of the ospAB operon and that increasing BosR expression leads to downregulation of OspA. Both regulatory sequences, cisI and cisII, showed strong BosR-binding and cisII bound much tighter than cisI. A promoterless bosR gene fused with an inducible promoter was introduced into an rpoS mutant and a wild-type strain to assess RpoS-independent and -dependent downregulation of OspA by BosR. With the induction of BosR expression, OspA expression was reduced more significantly in the RpoS-deficient than wild-type background, but not completely repressed. In the presence of constitutive expression of OspC, DbpA and DbpB, increasing BosR production resulted in complete repression of OspA in the RpoS mutant. Taken together, the study clearly demonstrated BosR serves as a repressor that binds both regulatory elements of the ospAB operon and shuts off expression.

The Cross-Talk between Spirochetal Lipoproteins and Immunity

Spirochetal diseases such as syphilis, Lyme disease, and leptospirosis are major threats to public health. However, the immunopathogenesis of these diseases has not been fully elucidated. Spirochetes interact with the host through various structural components such as lipopolysaccharides (LPS), surface lipoproteins, and glycolipids. Although spirochetal antigens such as LPS and glycolipids may contribute to the inflammatory response during spirochetal infections, spirochetes such as Treponema pallidum and Borrelia burgdorferi lack LPS. Lipoproteins are most abundant proteins that are expressed in all spirochetes and often determine how spirochetes interact with their environment. Lipoproteins are pro-inflammatory, may regulate responses from both innate and adaptive immunity and enable the spirochetes to adhere to the host or the tick midgut or to evade the immune system. However, most of the spirochetal lipoproteins have unknown function. Herein, the immunomodulatory effects of spirochetal lipoproteins are reviewed and are grouped into two main categories: effects related to immune evasion and effects related to immune activation. Understanding lipoprotein-induced immunomodulation will aid in elucidating innate immunopathogenesis processes and subsequent adaptive mechanisms potentially relevant to spirochetal disease vaccine development and to inflammatory events associated with spirochetal diseases.

Vaccination against Lyme disease: past, present, and future

Lyme borreliosis is a zoonotic disease caused by Borrelia burgdorferi sensu lato bacteria transmitted to humans and domestic animals by the bite of an Ixodes spp. tick (deer tick). Despite improvements in diagnostic tests and public awareness of Lyme disease, the reported cases have increased over the past decade to approximately 30,000 per year. Limitations and failed public acceptance of a human vaccine, comprised of the outer surface A (OspA) lipoprotein of B. burgdorferi, led to its demise, yet current research has opened doors to new strategies for protection against Lyme disease. In this review we discuss the enzootic cycle of B. burgdorferi, and the unique opportunities it poses to block infection or transmission at different levels. We present the correlates of protection for this infectious disease, the pros and cons of past vaccination strategies, and new paradigms for future vaccine design that would include elements of both the vector and the pathogen.

Reservoir targeted vaccine for lyme borreliosis induces a yearlong, neutralizing antibody response to OspA in white-footed mice

Lyme disease is caused by the spirochete Borrelia burgdorferi. The enzootic cycle of this pathogen requires that Ixodes spp. acquire B. burgdorferi from infected wildlife reservoirs and transmit it to other uninfected wildlife. At present, there are no effective measures to control B. burgdorferi; there is no human vaccine available, and existing vector control measures are generally not acceptable to the public. However, if B. burgdorferi could be eliminated from its reservoir hosts or from the ticks that feed on them, the enzootic cycle would be broken, and the incidence of Lyme disease would decrease. We developed OspA-RTV, a reservoir targeted bait vaccine (RTV) based on the immunogenic outer surface protein A (OspA) of B. burgdorferi aimed at breaking the natural cycle of this spirochete. White-footed mice, the major reservoir species for this spirochete in nature developed a systemic OspA-specific IgG response as a result of ingestion of the bait formulation. This immune response protected white-footed mice against B. burgdorferi infection upon tick challenge and cleared B. burgdorferi from the tick vector. In performing extensive studies to optimize the OspA-RTV for field deployment, we determined that mice that consumed the vaccine over periods of 1 or 4 months developed a yearlong, neutralizing anti-OspA systemic IgG response. Furthermore, we defined the minimum number of OspA-RTV units needed to induce a protective immune response.

Molecular interactions that enable movement of the Lyme disease agent from the tick gut into the hemolymph

Borrelia burgdorferi, the causative agent of Lyme disease, is transmitted to humans by bite of Ixodes scapularis ticks. The mechanisms by which the bacterium is transmitted from vector to host are poorly understood. In this study, we show that the F(ab)₂ fragments of BBE31, a B.burgdorferi outer-surface lipoprotein, interfere with the migration of the spirochete from tick gut into the hemolymph during tick feeding. The decreased hemolymph infection results in lower salivary glands infection, and consequently attenuates mouse infection by tick-transmitted B. burgdorferi. Using a yeast surface display approach, a tick gut protein named TRE31 was identified to interact with BBE31. Silencing tre31 also decreased the B. burgdorferi burden in the tick hemolymph. Delineating the specific spirochete and arthropod ligands required for B. burgdorferi movement in the tick may lead to new strategies to interrupt the life cycle of the Lyme disease agent.

Lyme disease, the most common tick-borne illness in North America, is caused by Borrelia burgdorferi. Currently, spirochete and tick molecules that facilitate Borrelia migration within the vector, a key step for mammalian infection by tick-transmitted spirochetes, have not yet been identified. In this study, we show that F(ab)₂ fragments of BBE31, a B.burgdorferi outer-surface lipoprotein, interfere with the spirochete migration from the tick gut into the hemolymph. Our results indicated that decreased hemolymph infection by blocking BBE31 resulted in lower salivary glands infection, which eventually attenuated murine infection by tick-transmitted B.burgdorferi. We also found that a tick gut protein TRE31 enables Borrelia movement by interacting with BBE31. This finding provides novel insights into the transmission of spirochete within the vector and provides potential vaccine targets to block the microbial life cycle within the vector.

Patterns and regulation of ribosomal RNA transcription in Borrelia burgdorferi

Background

Borrelia burgdorferi contains one 16S and two tandem sets of 23S-5S ribosomal (r) RNA genes whose patterns of transcription and regulation are unknown but are likely to be critical for survival and persistence in its hosts.

Results

RT-PCR of B. burgdorferi N40 and B31 revealed three rRNA region transcripts: 16S rRNA-alanine transfer RNA (tRNA^Ala); tRNA^Ile; and both sets of 23S-5S rRNA. At 34°C, there were no differences in growth rate or in accumulation of total protein, DNA and RNA in B31 cultured in Barbour-Stoenner-Kelly (BSK)-H whether rabbit serum was present or not. At 23°C, B31 grew more slowly in serum-containing BSK-H than at 34°C. DNA per cell was higher in cells in exponential as compared to stationary phase at either temperature; protein per cell was similar at both temperatures in both phases. Similar amounts of rRNA were produced in exponential phase at both temperatures, and rRNA was down-regulated in stationary phase at either temperature. Interestingly, a rel_Bbu deletion mutant unable to generate (p)ppGpp did not down-regulate rRNA at transition to stationary phase in serum-containing BSK-H at 34°C, similar to the relaxed phenotype of E. coli relA mutants.

Conclusions

We conclude that rRNA transcription in B. burgdorferi is complex and regulated both by growth phase and by the stringent response but not by temperature-modulated growth rate.

Antibodies against a tick protein, Salp15, protect mice from the Lyme disease agent

Traditionally, vaccines directly target a pathogen or microbial toxin. Lyme disease, caused by Borrelia burgdorferi, is a tick-borne illness for which a human vaccine is not currently available. B. burgdorferi binds a tick salivary protein, Salp15, during transmission from the vector, and this interaction facilitates infection of mice. We now show that Salp15 antiserum significantly protected mice from B. burgdorferi infection. Salp15 antiserum also markedly enhanced the protective capacity of antibodies against B. burgdorferi antigens, such as OspA or OspC. Mice actively immunized with Salp15 were also significantly protected from tick-borne Borrelia. In vitro assays showed that Salp15 antiserum increased the clearance of Salp15-coated B. burgdorferi by phagocytes, suggesting a mechanism of action. Vaccination with a vector molecule that a microbe requires for infection of the mammalian host suggests a new strategy for the prevention of Lyme disease, and this paradigm may be applicable to numerous arthropod-borne pathogens of medical importance.

Evidence that two ATP-dependent (Lon) proteases in Borrelia burgdorferi serve different functions

The canonical ATP-dependent protease Lon participates in an assortment of biological processes in bacteria, including the catalysis of damaged or senescent proteins and short-lived regulatory proteins. Borrelia spirochetes are unusual in that they code for two putative ATP-dependent Lon homologs, Lon-1 and Lon-2. Borrelia burgdorferi, the etiologic agent of Lyme disease, is transmitted through the blood feeding of Ixodes ticks. Previous work in our laboratory reported that B. burgdorferi lon-1 is upregulated transcriptionally by exposure to blood in vitro, while lon-2 is not. Because blood induction of Lon-1 may be of importance in the regulation of virulence factors critical for spirochete transmission, the clarification of functional roles for these two proteases in B. burgdorferi was the object of this study. On the chromosome, lon-2 is immediately downstream of ATP-dependent proteases clpP and clpX, an arrangement identical to that of lon of Escherichia coli. Phylogenetic analysis revealed that Lon-1 and Lon-2 cluster separately due to differences in the NH₂-terminal substrate binding domains that may reflect differences in substrate specificity. Recombinant Lon-1 manifested properties of an ATP-dependent chaperone-protease in vitro but did not complement an E. coli Lon mutant, while Lon-2 corrected two characteristic Lon-mutant phenotypes. We conclude that B. burgdorferi Lons -1 and -2 have distinct functional roles. Lon-2 functions in a manner consistent with canonical Lon, engaged in cellular homeostasis. Lon-1, by virtue of its blood induction, and as a unique feature of the Borreliae, may be important in host adaptation from the arthropod to a warm-blooded host.

Lyme disease, caused by the spirochete Borrelia burgdorferi, is the most prevalent arthropod-borne disease in North America. In nature, the bacterium oscillates between its tick vector host (Ixodes spp.) and small rodents (Peromyscus spp.). B. burgdorferi is able to persist in these two very different host environments by modulating the expression of surface lipoproteins proteins, or other proteins, in response to host factors or environmental cues such as temperature and pH. Our interest in this process led to the identification of a homolog of the E. coli ATP-dependent lon protease (lon-1) in B. burgdorferi that was upregulated in response to blood. The prototypical Lon of E. coli is a conserved protease important for the destruction of abnormal and short-lived proteins. B. burgdorferi is unusual in that it also codes for a second lon homolog, lon-2, that was not upregulated in response to blood. In this study, we sought to clarify the roles for Lon-1 and Lon-2 in B. burgdorferi. We present evidence that Lon-1 is an ATP- and Mg²⁺-dependent protease but does not function in a manner consistent with a prototypical Lon. Lon-2, however, functionally complemented Lon in E. coli. Thus, Lon-1 and Lon-2 appear to have distinct roles in B. burgdorferi; Lon-1 by virtue of its blood induction may be important in host adaptation, while Lon-2 is the functional homolog of E. coli Lon.

Human Lyme disease vaccines: past and future concerns

The development of a vaccine for Lyme disease was intensely pursued in the 1990s. However, citing a lack of demand, the first human Lyme disease vaccine was withdrawn from the market less than 5 years after its approval. The public's concerns about the vaccine's safety also likely contributed to the withdrawal of the vaccine. Nearly a decade later, no vaccine for human Lyme disease exists. The expansion of Lyme disease's endemic range, as well as the difficulty of diagnosing infection and the disease's steady increase in incidence in the face of proven preventative measures, make the pursuit of a Lyme disease vaccine a worthwhile endeavor. Many believe that the negative public perception of the Lyme disease vaccine will have tarnished any future endeavors towards its development. Importantly, many of the drawbacks of the Lyme disease vaccine were apparent or foreseeable prior to its approval. These pitfalls must be confronted before the construction of a new, effective and safe human Lyme disease vaccine.

Outer surface protein A protects Lyme disease spirochetes from acquired host immunity in the tick vector

The Lyme disease spirochete Borrelia burgdorferi alters the expression of outer surface protein (osp) genes as the bacterium cycles between ticks and mammals. OspA is produced as borreliae enter the tick vector and remains a major surface antigen during midgut colonization. To elucidate the role of OspA in the vector, we created an insertional deletion of ospA in strain B31-A3. The ospA mutant infects mice when it is injected intradermally and is acquired by larval ticks fed on these mice, where it persists through the molt to the nymph stage. Bacterial survival rates in artificially infected tick larvae fed on naïve mice were compared with those in the vector fed on immune mice. The ospA mutant proliferates in larvae if it is exposed to blood from naïve mice, but it declines in density after larval feeding if the blood is from immune mice. When uninfected larvae are fed on B-cell-deficient mice infected with the ospA mutant, larvae show borrelial densities and persistence that are significantly greater than those fed on infected, immunocompetent mice. We conclude that OspA serves a critical antibody-shielding role during vector blood meal uptake from immune hosts and is not required for persistence in the tick vector.

A reverse transcriptase-polymerase chain reaction assay of Borrelia burgdorferi 16S rRNA for highly sensitive quantification of pathogen load in a vector

We developed a real-time quantitative detection assay for the pathogen Borrelia burgdorferi, a Lyme borreliosis (LB) agent, using reverse transcription-polymerase chain reaction (RT-PCR) with primers and probe for a Borrelia genus-specific region of 16S ribosomal RNA. The standard curve of the assay was linear by semi-log plot over more than five orders of magnitude, and the detection limit of the assay was one thousandth of a single cell of B. burgdorferi. The minimum target level for detection using the RT-PCR assay for 16S RNA was 40-fold lower than the RT-PCR assay for messenger RNA of ospA, a highly expressed, plasmid-borne gene, and 1600-fold lower than the RT-PCR assay for messenger RNA of p66, a chromosome-borne gene of B. burgdorferi. The 16S rRNA assay was then applied in an experimental setting for monitoring the spirochetal load in B. burgdorferi-infected Ixodes scapularis ticks before and after they fed on Peromyscus leucopus mice immunized with recombinant OspA. Unfed infected ticks had a mean of 2,240 spirochetes per tick, and after feeding on non-immunized mice and engorgement, the mean number of spirochetes increased to 223,900 per tick. In contrast, there were either no or <or=7 spirochetes in ticks that had fed on OspA-immunized mice.

[Lyme disease: basis for treatment strategy, primary preventive care and secondary preventive care]

Lyme disease is the most common tick borne disease and is caused by Borrelia burgdorferi sensu lato. Ticks of the genus Ixodes are the vectors that transmit the infection to host mammals in endemic foci. Ixodes is infected by Borrelia at larval stage when it feeds on infected mammals. Man is an occasional host. The infection risk is linked to interaction between human and the natural environment. Strategies for prevention are closely related to the enzootic cycle of the Ixodes tick. Environmental measures to reduced tick density or host mammals are expensive, need to be repeated annually and cannot be applied to large areas. The primary prevention could be reduced to personal preventive measures such as reducing the amount of exposed skin and frequent checking for ticks. The risk of Lyme disease transmission after a tick bite is relatively low, and remains under 4%. The transmission rate depends on the duration of feeding. A rapide tick removal with fine tweezers or preferably special forceps and disinfection of the bite site appear to be the best technique. The absence of scientific evidence, and the risk of adverse events does not lead to recommending antimicrobial prophylaxis. Follow-up and educating the patients on the disease, clinical manifestation, and later primary prevention should be undertaken.

Identification of the etiologic agent of epizootic bovine abortion in field-collected Ornithodoros coriaceus Koch ticks

Epizootic bovine abortion (EBA), or foothill abortion as it has often been termed, is a tick-borne disease of pregnant cattle recognized in California, Nevada and Oregon. The primary objective of this study was to better define the relationship of a novel deltaproteobacterium, the putative etiological agent of EBA (aoEBA), with the Pajaroello tick (Ornithodoros coriaceus Koch), the recognized vector of EBA. Three developmental stages of O. coriaceus (larva, nymph, and adult) were collected from five locations in California, Nevada and Oregon. A polymerase chain reaction (PCR), developed for detection of aoEBA, was applied to DNA extracted from ticks. Southern blotting of the PCR products increased the number of ticks determined to be carrying the bacteria by seven-fold, suggesting the majority of infected ticks carry relatively low numbers of the pathogen. An effort was made to determine if an artificial blood meal would stimulate replication of the bacterial pathogen, thereby increasing the frequency in which aoEBA could be identified; no statistically significant effect was evident. The number of ticks determined to be carrying aoEBA varied with geographic location and ranged from 5 to 20%. aoEBA was found in both adults (12% of the males and 12% of the females) and nymphs (13%) but not larvae. Comparative analysis of dissected ticks provided strong evidence that the salivary gland was the most common location of aoEBA in field-collected ticks. No significant correlations were identified between the frequency of infection and tick weight, suggesting that increasing tick age and increased number of blood meals did not increase infectivity.

Development of an OspC-based tetravalent, recombinant, chimeric vaccinogen that elicits bactericidal antibody against diverse Lyme disease spirochete strains

Lyme disease is the most common arthropod-borne disease in North America and Europe. At present, there is no commercially available vaccine for use in humans. Outer surface protein C (OspC) has antigenic and expression characteristics that make it an attractive vaccine candidate; however, sequence heterogeneity has impeded its use as a vaccinogen. Sequence analyses have identified 21 well defined OspC phyletic groups or "types" (designated A-U). In this report we have mapped the linear epitopes presented by OspC types B, K, and D during human and murine infection and exploited these epitopes (along with the previously identified type A OspC linear epitopes) in the development of a recombinant, tetravalent, chimeric vaccinogen. The construct was found to be highly immunogenic in mice and the induced antibodies surface labeled in vitro cultivated spirochetes. Importantly, vaccination induced complement-dependent bactericidal antibodies against strains expressing each of the OspC types that were incorporated into the construct. These results suggest that an effective and broadly protective polyvalent OspC-based Lyme disease vaccine can be produced as a recombinant, chimeric protein.

Borrelia burgdorferi sensu stricto invasiveness is correlated with OspC-plasminogen affinity

Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, is transmitted through tick bite. Lyme borreliosis evolves in two stages: a primary red skin lesion called erythema migrans; later on, invasive bacteria disseminate to distant sites inducing secondary manifestations (neuropathies, arthritis, carditis, late skin disorders). It has been previously suggested that the ospC gene could be associated with invasiveness in humans depending on its sequence. Here, we confirm the pattern of invasiveness, according to B. burgdorferi sensu stricto (B. b. ss) ospC group, using the mouse as an experimental host of B. b. ss. As it has been shown that the host plasminogen activation system is used by B. burgdorferi to disseminate throughout the host, we studied the interaction of plasminogen with OspC proteins from invasive and non-invasive groups of B. b. ss. Using two methods, ELISA and surface plasmon resonance, we demonstrate that indeed OspC is a plasminogen-binding protein. Moreover, significant differences in binding affinity for plasminogen are correlated with different invasiveness patterns in mice. These results suggest that the correlation between ospC polymorphism and Borrelia invasiveness in humans is linked, at least in part, to differences in OspC affinity for plasminogen.

Immunoglobulin-regulated expression of Borrelia burgdorferi outer surface protein A in vivo

Borrelia burgdorferi, the agent of Lyme disease, down-regulates outer surface protein A (OspA), which is abundantly expressed in ticks, during infection of the mammalian host. In this study we examined the signals that may be responsible for maintaining the OspA-negative state of spirochetes during infection. Transcription of ospA mRNA was found in tissues of C3H-severe combined immunodeficient (C3H-scid) mice, but not immunocompetent C3H mice, inoculated with cultured B. burgdorferi, tick-borne spirochetes, and host-adapted spirochetes. Transcription was more frequent at 4 weeks than at 1 week. Transcription was present at the host-tick interface as early as 24 h after tick attachment but declined at 48 and 72 h. Thus, ospA mRNA transcription in distant tissues and at later times in C3H-scid mice is probably due to up-regulation during infection. Adoptive lymphocyte transfer from naive C3H mice to infected C3H-scid mice resulted in OspA seroconversion, confirming OspA expression in the host. Passive transfer of normal mouse serum, immunoglobulin M (IgM) from normal mouse serum, or IgG from normal mouse serum into infected C3H-scid mice resulted in down-regulation of ospA, but transfer of normal mouse serum depleted of immunoglobulin did not influence ospA mRNA transcription. Collectively, our results indicate that ospA mRNA transcription in the host is regulated by nonspecific immunoglobulin, which may be a natural antibody.

Interactions of OspA monoclonal antibody C3.78 with Borrelia burgdorferi within ticks

The Borrelia burgdorferi outer surface protein A (OspA) vaccine induces antibodies that prevent transmission from the tick to the host. Here we describe studies with an OspA monoclonal antibody (C3.78) to understand the mechanism by which antibodies entering the tick block Borrelia transmission. Host complement in the tick's blood meal did not contribute to protection because the antibody was equally effective whether infected ticks fed on normal or complement-deficient mice. Antibody-mediated cross-linking of bacteria or cross-linking of OspA molecules was not required for protection because C3.78 Fab' fragments were as effective as whole antibody molecules. At low C3.78 concentrations, transmission was blocked despite the presence of many live spirochetes within the tick, confirming that clearance of Borrelia organisms was not required to block transmission. We propose that OspA antibody binding to the surface of spirochetes blocks transmission by a mechanism that does not require bacterial killing.

Borrelia burgdorferi changes its surface antigenic expression in response to host immune responses

The Lyme disease spirochete, Borrelia burgdorferi, causes persistent mammalian infection despite the development of vigorous immune responses against the pathogen. To examine spirochetal phenotypes that dominate in the hostile immune environment, the mRNA transcripts of four prototypic surface lipoproteins, decorin-binding protein A (DbpA), outer surface protein C (OspC), BBF01, and VlsE, were analyzed by quantitative reverse transcription-PCR under various immune conditions. We demonstrate that B. burgdorferi changes its surface antigenic expression in response to immune attack. dbpA expression was unchanged while the spirochetes decreased ospC expression by 446 times and increased BBF01 and vlsE expression up to 20 and 32 times, respectively, under the influence of immune pressure generated in immunocompetent mice during infection. This change in antigenic expression could be induced by passively immunizing infected severe combined immunodeficiency mice with specific Borrelia antisera or OspC antibody and appears to allow B. burgdorferi to resist immune attack.

Outer membrane proteins of pathogenic spirochetes

Pathogenic spirochetes are the causative agents of several important diseases including syphilis, Lyme disease, leptospirosis, swine dysentery, periodontal disease and some forms of relapsing fever. Spirochetal bacteria possess two membranes and the proteins present in the outer membrane are at the site of interaction with host tissue and the immune system. This review describes the current knowledge in the field of spirochetal outer membrane protein (OMP) biology. What is known concerning biogenesis and structure of OMPs, with particular regard to the atypical signal peptide cleavage sites observed amongst the spirochetes, is discussed. We examine the functions that have been determined for several spirochetal OMPs including those that have been demonstrated to function as adhesins, porins or to have roles in complement resistance. A detailed description of the role of spirochetal OMPs in immunity, including those that stimulate protective immunity or that are involved in antigenic variation, is given. A final section is included which covers experimental considerations in spirochetal outer membrane biology. This section covers contentious issues concerning cellular localization of putative OMPs, including determination of surface exposure. A more detailed knowledge of spirochetal OMP biology will hopefully lead to the design of new vaccines and a better understanding of spirochetal pathogenesis.

Vaccines and immunotherapies for the prevention of infectious diseases having cutaneous manifestations

Although the development of antimicrobial drugs has advanced rapidly in the past several years, such agents act against only certain groups of microbes and are associated with increasing rates of resistance. These limitations of treatment force physicians to continue to rely on prevention, which is more effective and cost-effective than therapy. From the use of the smallpox vaccine by Jenner in the 1700s to the current concerns about biologic warfare, the technology for vaccine development has seen numerous advances. The currently available vaccines for viral illnesses include Dryvax for smallpox; the combination measles, mumps, and rubella vaccine; inactivated vaccine for hepatitis A; plasma-derived vaccine for hepatitis B; and the live attenuated Oka strain vaccine for varicella zoster. Vaccines available against bacterial illnesses include those for anthrax, Haemophilus influenzae, and Neisseria meningitidis. Currently in development for both prophylactic and therapeutic purposes are vaccines for HIV, herpes simplex virus, and human papillomavirus. Other vaccines being investigated for prevention are those for cytomegalovirus, respiratory syncytial virus, parainfluenza virus, hepatitis C, and dengue fever, among many others. Fungal and protozoan diseases are also subjects of vaccine research. Among immunoglobulins approved for prophylactic and therapeutic use are those against cytomegalovirus, hepatitis A and B, measles, rabies, and tetanus. With this progress, it is hoped that effective vaccines soon will be developed for many more infectious diseases with cutaneous manifestations.

Outer-surface protein C of the Lyme disease spirochete: a protein induced in ticks for infection of mammals

Environmentally responsive synthesis of surface proteins represents a hallmark of the infectious cycle of the Lyme disease agent, Borrelia burgdorferi. Here we created and analyzed a B. burgdorferi mutant lacking outer-surface protein C (OspC), an abundant Osp that spirochetes normally synthesize in the tick vector during the blood meal and down-regulate after transmission to the mammal. We demonstrate that B. burgdorferi strictly requires OspC to infect mice but not to localize or migrate appropriately in the tick. The induction of a spirochetal virulence factor preceding the time and host in which it is required demonstrates a developmental sequence for transmission of this arthropod-borne pathogen.

OspC facilitates Borrelia burgdorferi invasion of Ixodes scapularis salivary glands

Outer surface protein C (OspC) is a differentially expressed major surface lipoprotein of Borrelia burgdorferi. ospC is swiftly upregulated when spirochetes leave the Ixodes scapularis tick gut, migrate to the salivary gland, and exit the arthropod vector. Here we show that OspC strongly binds to the tick salivary gland, suggesting a role for OspC in spirochete adherence to this tissue. In vivo studies using a murine model of Lyme borreliosis showed that while OspC F(ab)(2) fragments did not influence either the viability of spirochetes or ospC gene expression, they did interfere with B. burgdorferi invasion of tick salivary glands. We then generated ospC knockout spirochetes in an infectious clone of B. burgdorferi and examined them within the vector. OspC-deficient or wild-type spirochetes persisted equally within the gut of unfed ticks and multiplied during the tick engorgement; however, unlike wild-type B. burgdorferi, the mutants were unable to invade salivary glands. Salivary gland colonization of OspC-deficient spirochetes was completely restored when this mutant was complemented in trans with a plasmid harboring the wild-type ospC gene. These studies conclusively demonstrate the importance of OspC in the invasion of tick salivary glands by B. burgdorferi, a critical step in the transmission of spirochetes from the arthropod vector to the mammalian host.

The Lyme disease vaccine takes its toll

Vaccination with Borrelia burgdorferi outer surface protein (Osp) A can induce a protective response against Lyme disease and serves as a model to understand the generation of protective immune responses against the spirochete. The innate response to pathogens is activated by specific Toll-like receptors (TLRs) that recognize distinct pathogen-associated molecular patterns. TLR2 is of particular interest for B. burgdorferi research because TLR2 recognizes several pathogen-associated molecular patterns, including lipoproteins. TLR2 may form heterodimers with TLR6 to identify diacylated lipoproteins, while TLR2 works in concert with TLR1 to recognize triacylated lipoproteins such as OspA. We will discuss the role of TLR1/2 in the development of responses to OspA in TLR1-and TLR2-deficient mice, and in selected individuals that received the OspA vaccine. While > 95% of human OspA-based Lyme disease vaccine recipients develop OspA antibodies, a very small group of individuals did not develop detectable humoral responses against OspA. We demonstrated that this hyporesponsiveness to OspA vaccination was associated with decreased cell surface expression of TLR1. Moreover, TLR1- and TLR2-deficient mice did not develop significant levels of OspA antibodies following vaccination with OspA, providing a correlation with human hyporesponsiveness to OspA. These data suggest that defects in the TLR1/2 signaling pathway are associated with an impaired ability to generate antibodies following immunization with OspA lipoprotein.

Direct detection methods for Lyme Borrelia, including the use of quantitative assays

Direct detection of Borrelia burgdorferi sensu lato, the etiologic agent of Lyme borreliosis, is the most reliable laboratory diagnostic tool. Several methods have been developed for direct detection of B. burgdorferi in infected vectors, host tissues, and clinical specimens from patients with Lyme borreliosis. These include microscope-based assays, antigen detection assays, in vitro cultivation, and nucleic acid-based detection of B. burgdorferi. The sensitivity and specificity of these methods depend on various factors and are also variable among laboratories. To date, only in vitro cultivation of B. burgdorferi has been widely accepted to confirm clinical diagnosis of Lyme borreliosis. Nevertheless, various polymerase chain reaction-based molecular assays have shown increasing significance in the laboratory diagnosis of Lyme borreliosis because of their high sensitivity, specificity, and capability for quantification and typing of spirochetes in clinical specimens. In this review, the currently available methods for direct detection of B. burgdorferi in clinical samples and quantitative analysis of spirochete load in different biological sources are discussed.

Dynamic changes in Borrelia burgdorferi populations in Ixodes scapularis (Acari: Ixodidae) during transmission: studies at the mRNA level

Many B. burgdorferi genes are regulated at the level of transcription during B. burgdorferi passage from ticks to mammals. Particular spirochete outer surface proteins of interest are OspA, OspC, and vlsE. The messenger RNA (mRNA) levels produced by these three genes were determined by a quantitative reverse transcription PCR (q-RT-PCR) procedure for spirochete populations in nymphal I. scapularis midguts and salivary glands at specific intervals during the feeding process. The mRNA values were compared to that of a standard, the mRNA levels of the constitutively expressed Flagellin (fla) gene. The levels of OspA and vlsE did not increase markedly in the midgut during feeding, but the mRNA levels of OspC increased significantly during feeding. In tick salivary glands, OspA mRNA levels actually decreased during feeding, while OspC levels increased six orders of magnitude. The mRNA levels of vlsE in tick salivary glands increased significantly only during the last 2 days of tick feeding. Overall, OspA mRNA was more abundant in tick midguts, whereas OspC and vlsE mRNA was more abundant in tick salivary glands. Further studies on the regulation of B. burgdorferi transcription activity during the act of transmission will lead to a better understanding of spirochete transmission dynamics, and hopefully facilitate the development of novel ways of interrupting the spread of Lyme disease.

Evaluation of Venezuelan Equine Encephalitis (VEE) replicon-based Outer surface protein A (OspA) vaccines in a tick challenge mouse model of Lyme disease

Venezuelan Equine Encephalitis (VEE) virus replicon particles (VRPs) encoding Borrelia burgdorferi Outer surface protein A (OspA) were evaluated for their ability to induce an immune response and provide protection from tick-borne spirochetes. VRPs expressing ospA that accumulated intracellularly (VRP OspA) or that was secreted from host cells (VRP tPA-OspA) were tested. Both VRP OspA and VRP tPA-OspA expressed ospA in immunized mice. Mice vaccinated with VRPs expressing secreted OspA produced significant amounts of anti-OspA antibodies, whereas VRPs expressing intracellular OspA were less immunogenic. The VRP method of delivery induced a Th1 type immune response unlike the recombinant OspA protein in Freund's adjuvant, which induced a mixed (Th1 and Th2) immune response. The VRP tPA-OspA construct induced an immune response that reduced the bacterial load in feeding Ixodes scapularis and blocked transmission to the host. These results indicate that VRPs are capable of providing protection against tick-borne B. burgdorferi, and potentially can be used for developing improved vaccines against Lyme disease.

A DNA vaccine encoding the outer surface protein C from Borrelia burgdorferi is able to induce protective immune responses

The outer surface protein C (OspC) of Borrelia burgdorferi, the spirochete that causes Lyme disease, is a promising candidate for a vaccine against borreliosis. BALB/c and C3H/HeJ mice were immunized either with recombinant OspC protein or with plasmid DNA encoding OspC fused to the human tissue plasminogen activator leader sequence (pCMV-TPA/ZS7). The influence of the route of administering the DNA and the use of oligodeoxynucleotides containing CpG-motifs on the development of the immune response was investigated. In both mouse strains, protein as well as gene-gun immunization induced Th2 type responses, whereas needle injection of plasmid DNA resulted in Th1 type antibody production. Co-injection of CpG-motifs did not significantly modify the response type in any immunization group, as indicated by only marginal changes of antibody subclass distribution. The protection rate after challenge with 10(4) B. burgdorferi organisms per mouse was between 80% and 100% for all groups. These results demonstrate, for the first time, that a DNA vaccine encoding OspC of B. burgdorferi is suitable for inducing protection against Lyme borreliosis.

Borrelia burgdorferi population dynamics and prototype gene expression during infection of immunocompetent and immunodeficient mice

The population dynamics of Borrelia burgdorferi were quantified by real-time PCR targeting the flaB gene in skin (inoculation site, noninoculation site, and ear), heart (heart base and ventricle), quadriceps muscle, and the tibiotarsal joint at 1, 2, 4, 6, and 8 weeks after intradermal inoculation in C3H and C3H-scid mice. In addition, RNA transcription was assessed for several prototype genes, including flaB, ospA, ospC, dbpA, arp, vlsE, fbp, oppA-2, and p37-42. Spirochete numbers were equivalent in C3H and C3H-scid mice at 1 or 2 weeks and then declined in C3H mice, but they continued to rise and then plateaued in C3H-scid mice. Gene transcription was likewise higher in C3H-scid mice than in C3H mice, particularly at 4 or more weeks of infection. Gene transcription showed variation among tissues, with the highest levels of transcription in heart and joint tissue, which are sites of inflammation.

Real-time PCR for simultaneous detection and quantification of Borrelia burgdorferi in field-collected Ixodes scapularis ticks from the Northeastern United States

The density of spirochetes in field-collected or experimentally infected ticks is estimated mainly by assays based on microscopy. In this study, a real-time quantitative PCR (qPCR) protocol targeting the Borrelia burgdorferi-specific recA gene was adapted for use with a Lightcycler for rapid detection and quantification of the Lyme disease spirochete, B. burgdorferi, in field-collected Ixodes scapularis ticks. The sensitivity of qPCR for detection of B. burgdorferi DNA in infected ticks was comparable to that of a well-established nested PCR targeting the 16S-23S rRNA spacer. Of the 498 I. scapularis ticks collected from four northeastern states (Rhode Island, Connecticut, New York, and New Jersey), 91 of 438 (20.7%) nymphal ticks and 15 of 60 (25.0%) adult ticks were positive by qPCR assay. The number of spirochetes in individual ticks varied from 25 to 197,200 with a mean of 1,964 spirochetes per nymphal tick and a mean of 5,351 spirochetes per adult tick. No significant differences were found in the mean numbers of spirochetes counted either in nymphal ticks collected at different locations in these four states (P = 0.23 by one-way analysis of variance test) or in ticks infected with the three distinct ribosomal spacer restriction fragment length polymorphism types of B. burgdorferi (P = 0.39). A high degree of spirochete aggregation among infected ticks (variance-to-mean ratio of 24,877; moment estimate of k = 0.279) was observed. From the frequency distribution data and previously published transmission studies, we estimated that a minimum of 300 organisms may be required in a host-seeking nymphal tick to be able to transmit infection to mice while feeding on mice. These data indicate that real-time qPCR is a reliable approach for simultaneous detection and quantification of B. burgdorferi infection in field-collected ticks and can be used for ecological and epidemiological surveillance of Lyme disease spirochetes.

OspA immunization decreases transmission of Borrelia burgdorferi spirochetes from infected Peromyscus leucopus mice to larval Ixodes scapularis ticks

Recombinant outer surface protein A (OspA) vaccination of wild animal reservoirs has potential application for reducing Borrelia burgdorferi transmission in nature and subsequent risk of human infection. As a major reservoir host, the white-footed mouse (Peromyscus leucopus) is a candidate for a vaccination program designed to reduce infection prevalence in vector ticks. In this study we characterized the effect of various levels of immunization with recombinant OspA-glutathione transferase fusion protein on transmission dynamics from infected P. leucopus to larval ticks. Control mice were vaccinated with glutathione transferase alone. All mice were experimentally infected with B. burgdorferi before vaccination. The immune responses of the immunized mice were assessed by enzyme-linked immunosorbent assay for antibodies to OspA. Transmission of B. burgdorferi from infected mice was determined by xenodiagnosis with uninfected larval ticks. Spirochetes in ticks were counted by direct immunofluorescence assay. The concentration of antibody to OspA increased with each OspA vaccination but most markedly after the first and second vaccinations. In comparison with control mice, there was reduced transmission by OspA-vaccinated mice to uninfected ticks. One, two, or three doses of OspA reduced infection prevalence in xenodiagnostic ticks by 48%, 92%, or 99% and the numbers of spirochetes per tick by 84%, 98%, or 99%, respectively. This study suggests that vaccination of P. leucopus with OspA could reduce transmission to the tick vector in nature despite prior infection of the reservoir host.

Characterization of the stringent response and rel(Bbu) expression in Borrelia burgdorferi

The stringent response is a global bacterial response to nutritional stress mediated by (p)ppGpp. We previously found that both noninfectious Borrelia burgdorferi strain B31 and infectious B. burgdorferi strain N40 produced large amounts of (p)ppGpp during growth in BSK-H medium and suggested that the stringent response was triggered in B. burgdorferi under these conditions. Here we report that (p)ppGpp levels in B. burgdorferi growing in BSK-II or BSK-H medium are not further increased by nutrient limitation or by serine hydroxamate-induced inhibition of protein synthesis and that the presence of (p)ppGpp during growth of N40 in BSK-H medium is not associated with decreased 16S rRNA synthesis. Decreased 16S rRNA synthesis was associated with the decreased growth rate of N40 seen during coculture with tick cells, which are growth conditions that were previously shown to decrease (p)ppGpp levels. One-half as much of the mRNA of the gene encoding the Rel protein of B. burgdorferi (rel(Bbu)) was produced by B31 as by N40 during in vitro growth (2 +/- 0.5 and 4 +/- 0.8 fg of rel(Bbu) mRNA/ng of total Borrelia RNA, respectively). Although the amounts of N40 rel(Bbu) mRNA were identical during growth in vitro and in rat peritoneal chambers, they were markedly decreased during growth in nymphal ticks. In contrast to the lack of change in rel(Bbu) mRNA levels, larger amounts of a 78-kDa protein that was cross-reactive with antibodies to Bacillus subtilis Rel(Bsu) were detected in immunoblots of N40 lysates after growth in rat peritoneal chambers than after growth in vitro. Differences in the level of production of (p)ppGpp between B31 and N40 could not be explained by differences in rel(Bbu) promoters since identical transcriptional start sites 309 nucleotides upstream from the B31 and N40 rel(Bbu) ATG start codon and identical sigma(70)-like promoters were identified by primer extension and sequencing analysis. rel(Bbu) complemented an Escherichia coli CF1693 relA spoT double mutant for growth on M9 minimal medium, and the transformed cells produced rel(Bbu) mRNA. These results indicate that rel(Bbu) is functional and that its transcription and translation and production of (p)ppGpp are affected by environmental conditions in strains N40 and B31. They also suggest that in B. burgdorferi, an organism with few rRNA operons that grows slowly, the role of (p)ppGpp may differ from the classic role played by this molecule in E. coli and that (p)ppGpp may not be responsible for growth rate control.

Hyporesponsiveness to vaccination with Borrelia burgdorferi OspA in humans and in TLR1- and TLR2-deficient mice

The Lyme disease vaccine is based on the outer-surface lipoprotein (OspA) of the pathogen Borrelia burgdorferi, and 95% of vaccine recipients develop substantial titers of antibodies against OspA. Here, we identified seven individuals with very low antibody titers after vaccination (low responders). The macrophages of low responders produced less tumor necrosis factor-alpha and interleukin-6 after OspA stimulation and had lower cell-surface expression of Toll-like receptor (TLR) 1 as compared to normal cells, but normal expression of TLR2. TLRs activate innate responses to pathogens, and TLR2 recognizes lipoproteins and peptidoglycan (PGN). After OspA immunization, mice genetically deficient in either TLR2 (TLR2(-/-)) or TLR1 (TLR1(-/-)) produced low titers of antibodies against OspA. Notably, macrophages from TLR2(-/-) mice were unresponsive to OspA and PGN, whereas those from TLR1(-/-) mice responded normally to PGN but not to OspA. These data indicate that TLR1 and TLR2 are required for lipoprotein recognition and that defects in the TLR1/2 signaling pathway may account for human hyporesponsiveness to OspA vaccination.

Borrelia burgdorferi population kinetics and selected gene expression at the host-vector interface

By using real-time quantitative PCR, the population dynamics and gene transcription of Borrelia burgdorferi were examined in ticks and skin of mice during acquisition of the infection from mice by ticks and during transmission of the infection from ticks to mice. Population dynamics were determined by using a flaB DNA target. A quantitative analysis of flaB, ospA, ospC, dbpA, and arp transcription was also performed. The results revealed that both uninfected larval and nymphal Ixodes scapularis ticks acquired B. burgdorferi as early as 1 day after attachment and that the sizes of spirochete populations within ticks increased during feeding. In addition, all gene targets revealed that there was RNA transcription during feeding. Similar events occurred within infected nymphal ticks feeding on uninfected hosts. Transmission from infected nymphal ticks to mice could be detected within 1 day after attachment. Analysis of skin during the first 3 days after attachment of infected ticks revealed rising numbers of spirochetes but minimal gene transcription. In contrast, the skin of mice with established infections revealed static populations of spirochetes and active but stable transcription of flaB, ospC, dbpA, and arp. There were consistent reductions in the number of spirochetes in the skin at the tick attachment sites compared to the number of spirochetes in the skin at nontick sites, but there were no differences in gene expression between tick and nontick skin sites. Evidence of ospA transcription in skin could be found 1 day after tick attachment but not thereafter.

Genetic diversity of the outer surface protein C gene of southern Borrelia isolates and its possible epidemiological, clinical, and pathogenetic implications

The ospC genes of 20 southern Borrelia strains were sequenced. The strains consisted of B. burgdorferi sensu stricto, B. andersonii, B. bissettii, one undescribed genospecies, MI-8, and one probably new Borrelia species, TXW-1. A high degree of similarity exists between B. burgdorferi sensu stricto and B. bissettii and between B. bissettii and B. andersonii. Lateral transfers of the ospC gene probably occurred between B. burgdorferi sensu stricto and B. bissettii and between B. bissettii and B. andersonii. Internal gene recombination appears to occur among them. The highest degree of genetic diversity among them was observed in the two variable domains (V1 and V2), semivariable domain (SV), and the species-specific epitopes (between amino acids 28 and 31). Differences in ospC sequences among southern strains reflect diversity at the strain and genospecies levels. MI-8, which was recognized as an undescribed genospecies in our previous reports, remains distinguishable in our current analysis of ospC genes and is distinct from B. burgdorferi sensu stricto. Interestingly, another undescribed southern isolate, TXW-1, was not amplified under various PCR conditions. Compared to European B. burgdorferi sensu stricto strains, American B. burgdorferi sensu stricto strains show greater genetic heterogeneity. Southern B. burgdorferi sensu stricto, B. andersonii, and B. bissettii isolates were intermixed with each other in the phylogenetic trees. In the derived trees in our work, at least one southeastern strain of B. burgdorferi, MI-2, most closely aligns with a so-called invasive cluster that possesses many proven human-invasive strains. Transmission experiments show that MI-2 and the strains in this group of southern spirochetes are able to infect mice and hamsters and that the typical vector of Lyme disease, Ixodes scapularis, can acquire the spirochetes from infected mammals. Currently, strain MI-2 appears to be the only southern isolate among the 20 we analyzed that clusters with an OspC invasive group and thus might be invasive for humans.

Prevention of tick-borne diseases

Ticks are a part of the landscape where humans live, work, and play. Because ticks carry a wide range of organisms that potentially can cause disease in humans, many studies have focused on ways to reduce risk of these diseases. Ticks have biologically complex interactions with microorganisms and with their vertebrate hosts, on whom they depend for blood meals and survival. To consider ways to reduce the burden of tick-borne diseases in humans, it is necessary to understand the biology and ecology of ticks and their interface with humans. In many areas, changes in land use, reforestation, and patterns of human settlements have led to more abundant tick populations, increasing rates of infections in ticks, and increasing contact with human populations. Warmer winter temperatures in temperate regions may extend the transmission season for some ticks and pathogens. Although much of the discussion in this article has focused on I. scapularis and the Lyme disease spirochete (because they have been studied extensively), other tick-pathogen pairs may differ in risk factors for infection and transmission dynamics. Interventions studied to reduce the burden of tick-borne diseases include changing the environment, controlling vertebrate hosts, killing ticks, altering the behavior of humans, treating tick bites, and trying to protect humans through immunologic means (vaccine). All of these approaches have limitations and drawbacks. From a public health perspective, a plan that employs multiple strategies may be most effective. This article has reviewed what is known about preventive interventions, including the vaccine.

Laboratory testing for suspected Lyme disease

Laboratory testing for B. burgdorferi infection is intended to substantiate a physician's clinical judgment of whether a patient has Lyme disease or not. Cultivation of B. burgdorferi from a patient's skin or blood is the gold standard for demonstration of active infection, but it is expensive and lacks clinical sensitivity. Detection of spirochetal DNA in clinical samples by PCR has better sensitivity, but PCR for B. burgdorferi has not yet been standardized for more routine diagnostic testing. Detection of antibodies to B. burgdorferi is the most practical and common approach for laboratory work-up of a case of suspected Lyme disease. Serologic assays fall short of 100% sensitivity and specificity, however, and examination of a single specimen in time does not discriminate between previous and ongoing infection. Because of a background false positivity even among healthy populations of nonendemic regions, serologic testing is recommended only when there is at least a one in five chance, in the physician's estimation, that the patient has active Lyme disease. The pretest likelihood of the disease is determined by the physician in the context of epidemiologic and clinical facts of the case. This estimate can serve to reassure patients who are at low risk of B. burgdorferi infection but are seeking a Lyme test for complaints of a more nonspecific nature. Although new subunit serologic assays based on recombinant proteins are becoming available commercially, the longstanding two-test approach, in which a positive or indeterminate result with a standardized, sensitive ELISA test is followed by verification with a more specific Western blot assay, still provides the physician with a reasonably accurate and reliable assessment of the presence of antibodies to B. burgdorferi. More recent challenges for serologic testing are seropositivity in the population as the result of immunization with the Lyme disease vaccine and the emergence of new Borrelia species that cause Lyme disease-like illnesses.

Adverse event reports following vaccination for Lyme disease: December 1998-July 2000

CONTEXT

The vaccine adverse event reporting system (VAERS) monitors vaccine safety post-licensure. Although events reported to VAERS are not necessarily causally associated with vaccination, VAERS reports can be used to identify possible safety concerns that occur at too low a rate to have been identified prior to licensure.

OBJECTIVE

To evaluate adverse events following Lyme disease vaccination reported to VAERS during the first 19 months of the vaccine's licensure.

DESIGN, SETTING, AND PARTICIPANTS

Analysis of all VAERS reports of adverse events following vaccination for Lyme disease in the US from 28 December 1998 to 31 July 2000.

MAIN OUTCOME MEASURE

We evaluated reported adverse events for unexpected patterns in age, gender, time to onset, dose number, and clinical characteristics and compared them to adverse events observed in clinical trials of this vaccine.

RESULTS

Over 1,400,000 doses were distributed and 905 adverse events were reported to VAERS, 440 in men and 404 in women, with ages ranging from 10 to 82 years. The majority (56%) of adverse events occurred after administration of the first dose. The most frequently reported adverse events were arthralgia (250), myalgia (195), and pain (157). There were 59 reports coded as arthritis, 34 as arthrosis, 9 as rheumatoid arthritis, and 12 as facial paralysis. Sixty-six (7.4%) events were classified as serious, involving life-threatening illness, hospitalization, prolongation of hospitalization, persistent or significant disability/incapacity, or death. Twenty-two hypersensitivity reactions were reported.

CONCLUSION

Based on reporting to VAERS, we did not detect unexpected or unusual patterns of reported adverse events following Lyme disease vaccine administration, other than hypersensitivity reactions, compared with adverse events observed in clinical trials.