Evaluation of whole-cell and OspC enzyme-linked immunosorbent assays for discrimination of early lyme borreliosis from OspA vaccination

Laboratory Diagnosis of Lyme Borreliosis

Lyme borreliosis is caused by a growing list of related, yet distinct, spirochetes with complex biology and sophisticated immune evasion mechanisms. It may result in a range of clinical manifestations involving different organ systems, and can lead to persistent sequelae in a subset of cases. The pathogenesis of Lyme borreliosis is incompletely understood, and laboratory diagnosis, the focus of this review, requires considerable understanding to interpret the results correctly. Direct detection of the infectious agent is usually not possible or practical, necessitating a continued reliance on serologic testing. Still, some important advances have been made in the area of diagnostics, and there are many promising ideas for future assay development. This review summarizes the state of the art in laboratory diagnostics for Lyme borreliosis, provides guidance in test selection and interpretation, and highlights future directions.

Borrelia burgdorferi Infection and Lyme Disease in North American Horses: A Consensus Statement

Borrelia burgdorferi infection is common in horses living in Lyme endemic areas and the geographic range for exposure is increasing. Morbidity after B. burgdorferi infection in horses is unknown. Documented, naturally occurring syndromes attributed to B. burgdorferi infection in horses include neuroborreliosis, uveitis, and cutaneous pseudolymphoma. Although other clinical signs such as lameness and stiffness are reported in horses, these are often not well documented. Diagnosis of Lyme disease is based on exposure to B. burgdorferi, cytology or histopathology of infected fluid or tissue and antigen detection. Treatment of Lyme disease in horses is similar to treatment of humans or small animals but treatment success might not be the same because of species differences in antimicrobial bioavailability and duration of infection before initiation of treatment. There are no approved equine label Lyme vaccines but there is strong evidence that proper vaccination could prevent infection in horses.

Antibody responses to Borrelia burgdorferi outer surface proteins C and F in experimentally infected Beagle dogs

Antibody levels to outer surface proteins C and F (OspC and OspF, respectively) in sera collected from laboratory Beagle dogs at 1, 2, and 4 months after challenge with infected black-legged ticks (Ixodes scapularis) were determined. Each dog was confirmed by culture to harbor Borrelia burgdorferi in the skin (n = 10) or the skin and joints (n = 14). Significant levels of immunoglobulin M (Ig)M or IgG anti-OspC antibodies were detected in single serum samples from only 3 (13%) dogs. Similarly, IgM anti-OspF antibodies were detected in only 1 (4%) serum sample collected from a dog with B. burgdorferi in the skin and joints. In contrast, 4 (29%) dogs with skin and joint infections produced IgG anti-OspF antibodies after 2 months, and the response expanded to include 2 (20%) dogs with skin infection and 4 additional dogs with skin and joint infections (overall sensitivity = 62%) after 4 months. The findings failed to support the utility of OspC-based antibody tests for diagnosing canine Lyme disease, but demonstrated that dogs with B. burgdorferi colonizing joint tissue most often produced significant levels of IgG anti-OspF antibodies. Therefore, additional studies to more thoroughly evaluate the clinical utility of OspF-based antibody tests are warranted.

Antibodies to Borrelia burgdorferi OspA, OspC, OspF, and C6 antigens as markers for early and late infection in dogs

Lyme disease in the United States is caused by Borrelia burgdorferi sensu stricto, which is transmitted to mammals by infected ticks. Borrelia spirochetes differentially express immunogenic outer surface proteins (Osp). Our aim was to evaluate antibody responses to Osp antigens to aid the diagnosis of early infection and the management of Lyme disease. We analyzed antibody responses during the first 3 months after the experimental infection of dogs using a novel multiplex assay. Results were compared to those obtained with two commercial assays detecting C6 antigen. Multiplex analysis identified antibodies to OspC and C6 as early as 3 weeks postinfection (p.i.) and those to OspF by 5 weeks p.i. Antibodies to C6 and OspF increased throughout the study, while antibodies to OspC peaked between 7 and 11 weeks p.i. and declined thereafter. A short-term antibody response to OspA was observed in 3/8 experimentally infected dogs on day 21 p.i. Quant C6 enzyme-linked immunosorbent assay (ELISA) results matched multiplex results during the first 7 weeks p.i.; however, antibody levels subsequently declined by up to 29%. Immune responses then were analyzed in sera from 125 client-owned dogs and revealed high agreement between antibodies to OspF and C6 as robust markers for infection. Results from canine patient sera supported that OspC is an early infection marker and antibodies to OspC decline over time. The onset and decline of antibody responses to B. burgdorferi Osp antigens and C6 reflect their differential expression during infection. They provide valuable tools to determine the stage of infection, treatment outcomes, and vaccination status in dogs.

Development of a multiplex assay for the detection of antibodies to Borrelia burgdorferi in horses and its validation using Bayesian and conventional statistical methods

Lyme disease is a zoonotic, vector-borne disease and occurs in mammals including horses. The disease is induced by infection with spirochetes of the Borrelia burgdorferi sensu lato group. Infection of mammalian hosts requires transmission of spirochetes by infected ticks during tick bites. Lyme disease diagnosis is based on clinical signs, possible exposure to infected ticks, and antibody testing which is traditionally performed by ELISA and Western blotting (WB). This report describes the development and validation of a new fluorescent bead-based multiplex assay for the detection of antibodies to B. burgdorferi outer surface protein A (OspA), OspC and OspF antigens in horse serum. Testing of 562 equine sera was performed blindly and in parallel by using WB and the new multiplex assay. Because a true gold standard is missing for Lyme antibody testing, we performed and compared different statistical approaches to validate the new Lyme multiplex assay. One approach was to use WB results as a 'relative gold standard' in ROC-curve and likelihood-ratio analyses of the new test. Cut-off values and interpretation ranges of the multiplex assay were established by the analysis. The second statistical approach used a Bayesian model for the calculation of diagnostic sensitivities and specificities of the multiplex assay. The Bayesian analysis takes into consideration that no true gold standard exists for detecting antibodies to B. burgdorferi and estimated sensitivities and specificities of both tests that were compared. Therefore, the Bayesian analysis also resulted in an evaluation of diagnostic sensitivity and specificity of WB. Overall, the new assay was characterized by low background values and a wide dynamic quantification range for the detection of antibodies to OspA, OspC and OspF antigens of B. burgdorferi. The diagnostic sensitivity and specificity for the OspA bead-based assay were calculated as 49% and 85%, respectively, and by a standard ROC curve analysis only because the Bayesian model could not be run on this parameter. The Bayesian-derived diagnostic sensitivities of the OspC and OspF assays were 80% and 86%, respectively. For comparison, the Bayesian-derived estimates for WB resulted in sensitivities of 72% for OspC and 80% for OspF. The Bayesian diagnostic specificities of the multiplex assay were 79% and 69% for OspC and OspF, respectively. WB analysis had specificities of 92% for OspC and 77% for OspF. Although the analysis of a new assay in the absence of a true gold standard remains challenging, the approach used here can help to address this problem when new technologies and traditionally used test standards differ significantly in their analytical sensitivities, which consequently causes problems in the calculation of diagnostic sensitivity and sensitivity values for the new assay. In summary, the new multiplex assay for the detection of antibodies to B. burgdorferi OspA, OspC and OspF antigens in horse serum has improved analytical and diagnostic sensitivities compared to WB analysis. Multiplex analysis is a valuable quantitative tool that simultaneously detects antibodies indicative for natural infection with and/or vaccination against the Lyme pathogen.

Population-based study of diagnostic assays for Borrelia infection: comparison of purified flagella antigen assay (Ideia, Dako Cytomation) and recombinant antigen assay (Liaison, DiaSorin)

Background

Testing for Borrelia-specific IgM and IgG-antibodies are often performed on a variety of poorly defined symptoms, and isolated IgM results are a frequent finding, which results in diagnostic uncertainty and further testing. We wanted to test the hypothesis that Borrelia-specific assays using recombinant antigens perform differently from assays based on purified flagella antigen.

Methods

We compared the use of recombinant antigens (LIAISON^® DiaSorin, Saluggia, Italy) and purified flagella antigen (IDEIA™ Borrelia, DakoCytomation, Glostrup, Denmark) in the assay for Borrelia-specific IgM and IgG-antibodies. The assays were tested on an unselected population of serum samples submitted from general practice. A total of 357 consecutive samples for analysis of Borrelia IgM and IgG antibodies. Furthermore, we analysed 540 samples for Borrelia-specific IgM or IgG antibodies first by the IDEIA™ and, if they were positive, the samples were further analysed using the LIAISON^® assay. To verify the correctness of the patient's serological status, discrepant samples were analysed by line blots (EcoLine, Virotech).

Results

In the consecutive series of 357 samples, the IgM assays detected 308 negative and 3 positive samples with concordant results. Compared with the line blot, the IDEIA™ system produced 21 false-positive IgM results, whereas the LIAISON^® system produced only one false-positive IgM result. The IgG assays showed 1 positive and 328 negative concordant results. The LIAISON^® system produced 9 true IgG-positive samples that were not detected by the IDEIA™ system, but the former produced 4 positive IgG results that were negative by line blot.

Conclusion

Diagnostic assays based on flagella antigen seem to show more false-positive IgM and false-negative IgG results than assays based on recombinant antigens. The latter may reduce the number of presumably false-positive IgM results and identify more IgG-positive subjects, but this system also produces more false-positive IgG results.

Significantly improved accuracy of diagnosis of early Lyme disease by peptide enzyme-linked immunosorbent assay based on the borreliacidal antibody epitope of Borrelia burgdorferi OspC

Highly specific borreliacidal antibodies are induced by infection with Borrelia burgdorferi, and the immunodominant response during early Lyme disease is specific for an epitope within the 7 amino acids nearest the C terminus of OspC. We evaluated the ability of an enzyme-linked immunosorbent assay (ELISA) based on a synthetic peptide (OspC7) that matched the region to detect the response and compared the sensitivity during early Lyme disease to that for an FDA-approved Western blot. When the optical density value was adjusted to 98% specificity based on the results from testing normal or uncharacterized sera (n = 236) or sera from patients with blood factors or illnesses that commonly produce antibodies that cross-react with B. burgdorferi antigens (n = 77), 115 (73%) of 157 sera from patients likely to have early Lyme disease were positive for immunoglobulin M (IgM) antibodies and 17 (11%) also had IgG antibodies. In addition, the IgM ELISA reactivities and the titers of antibodies detected by a flow cytometric borreliacidal antibody test correlated closely (r = 0.646). Moreover, the IgM ELISA was significantly more sensitive (P < 0.001) than the Western blot procedure. The findings therefore confirmed that the peptide IgM ELISA detected OspC borreliacidal antibodies and provided strong evidence that the test can eliminate the necessity for confirming early Lyme disease by a supplementary test such as Western blotting.

Borreliacidal OspC antibody response of canines with Lyme disease differs significantly from that of humans with Lyme disease

Humans reliably produce high concentrations of borreliacidal OspC antibodies specific for the seven C-terminal amino acids shortly after infection with Borrelia burgdorferi. We show that dogs also produce OspC borreliacidal antibodies but that their frequencies, intensities, and antigenicities differ significantly. The findings therefore confirm a major difference between the borreliacidal antibody responses of humans and canines with Lyme disease.

Borreliacidal OspC antibodies specific for a highly conserved epitope are immunodominant in human lyme disease and do not occur in mice or hamsters

Humans produce highly specific borreliacidal antibodies against outer surface protein C (OspC) shortly after infection with Borrelia burgdorferi sensu stricto. We previously demonstrated the epitope recognized by immunoglobulin M (IgM) and IgG OspC borreliacidal antibodies was located within the 50 amino acids nearest the carboxy (C) terminus. In this study, we show the immunodominant epitope is located in the highly conserved region within the seven C-terminal amino acids. Six early Lyme disease sera that contained borreliacidal activity and IgM and/or IgG OspC antibodies were chosen randomly and adsorbed with truncated OspC containing the 16 or 7 amino acids nearest the C terminus. Adsorptions with each truncated protein abrogated the borreliacidal activity completely. In addition, only small concentrations of OspC antibodies remained detectable by enzyme-linked immunosorbent assay and Western blotting. Moreover, borreliacidal OspC antibodies were not induced in laboratory mice or hamsters despite heavy infections with B. burgdorferi spirochetes. These findings confirm that borreliacidal antibodies comprise the majority of the IgM and IgG OspC antibody response in human Lyme disease and that the epitope is located in the highly conserved C terminus. In addition, rodent animal models appear to be inappropriate subjects for assessing the effectiveness of the epitope for serodiagnosis or as a human Lyme disease vaccine.

C-terminal region of outer surface protein C binds borreliacidal antibodies in sera from patients with Lyme disease

Borreliacidal antibodies specific for outer surface protein C (OspC) are induced shortly after infection with Borrelia burgdorferi. In this study, we identified the region of OspC recognized by immunoglobulin M (IgM) and IgG borreliacidal antibodies. Sera from patients with early Lyme disease were screened for borreliacidal activity specific for B. burgdorferi 50772 and OspC antibodies. Seven sera that contained similarly high titers of each response were then chosen randomly and adsorbed with OspC or a truncated OspC (OspC-Dra) containing the 50 amino acids nearest the carboxy terminus. Adsorption with OspC or OspC-Dra completely eliminated the borreliacidal activity in six (86%) of seven sera and significantly decreased the activity in the remaining serum (titer of 10,240 to 1,280). Moreover, OspC antibodies were no longer detected by OspC enzyme-linked immunosorbent assay or in a Western blot that contained native OspC. The findings confirmed that sera from patients with early Lyme disease contain high concentrations of IgM or IgG borreliacidal antibodies that bind a conserved region of OspC.

Comparison of the Borrelia DotBlot G, MarDx, and VIDAS enzyme immunoassays for detecting immunoglobulin G antibodies to Borrelia burgdorferi in human serum

Three enzyme immunoassays, Borrelia DotBlot G (GenBio, San Diego, Calif.), MarDx EIA (MarDx Diagnostics, Inc., Carlsbad, Calif.), and VIDAS (bioMérieux, St. Louis, Mo.) were compared for their ability to detect immunoglobulin G antibodies to Borrelia burgdorferi in 100 human serum samples. The "gold standard" positive result for each of these samples was determined by Western immunoblot analysis (MarDx Marblot Test System) (n = 99) or clinical signs and symptoms suggestive of Lyme disease with other laboratory results positive for B. burgdorferi (n = 1). Based on these criteria for a gold standard positive result, 29 of the 100 samples tested were considered true positives and 71 were considered true negatives. The following sensitivities and specificities were noted, respectively, for each method: Borrelia DotBlot G, 93 and 90%; MarDx, 100 and 35%; and VIDAS, 100 and 92%. Because of high sensitivity and specificity and ease of use, the VIDAS test is an appealing method, especially for laboratories that perform high volumes of tests. The high sensitivity but low specificity of the MarDx method compared to the VIDAS and Borrelia DotBlot G methods requires that Western blot confirmatory tests be performed frequently. The Borrelia DotBlot G method has acceptable specificity but appears to lack sensitivity when compared to the VIDAS and MarDx methods.

OspE-related, OspF-related, and Elp lipoproteins are immunogenic in baboons experimentally infected with Borrelia burgdorferi and in human lyme disease patients

Presently, the rhesus macaque is the only nonhuman primate animal model utilized for the study of Lyme disease. While this animal model closely mimics human disease, rhesus macaques can harbor the herpes B virus, which is often lethal to humans; macaques also do not express the full complement of immunoglobulin G (IgG) subclasses found in humans. Conversely, baboons contain the full complement of IgG subclasses and do not harbor the herpes B virus. For these reasons, baboons have been increasingly utilized as the basis for models of infectious diseases and studies assessing the safety and immunogenicity of new vaccines. Here we analyzed the capability of baboons to become infected with Borrelia burgdorferi, the agent of Lyme disease. Combined culture and PCR analyses of tick- and syringe-infected animals indicated that baboons are a sufficient host for B. burgdorferi. Analysis of the antibody responses in infected baboons over a 48-week period revealed that antibodies are generated early during infection against many borrelial antigens, including the various OspE, OspF, and Elp paralogs that are encoded on the ubiquitous 32-kb circular plasmids (cp32s). By using the baboon sera generated by experimental infection it was determined that a combination of two cp32-encoded lipoproteins, OspE and ElpB1, resulted in highly specific and sensitive detection of B. burgdorferi infection. An expanded analysis, which included 39 different human Lyme disease patients, revealed that a combination of the OspE and ElpB1 lipoproteins could be the basis for a new serodiagnostic assay for Lyme disease. Importantly, this novel serodiagnostic test would be useful independent of prior OspA vaccination status.

Evaluation of the C6 peptide enzyme-linked immunosorbent assay for individuals vaccinated with the recombinant OspA vaccine

The C6 enzyme-linked immunosorbent assay (ELISA), based on a peptide (C6) that reproduces the sequence of invariable region 6 of VlsE, the antigenic variation protein of Borrelia burgdorferi, has been shown to be a sensitive and specific test for the serologic diagnosis of Lyme disease. We now report that none of 29 uninfected individuals vaccinated with the recombinant OspA vaccine had an antibody response to the C6 peptide. The C6 peptide ELISA can be used to diagnose Lyme disease in patients who have received the OspA vaccine.

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.

Recombinant assay for serodiagnosis of Lyme disease regardless of OspA vaccination status

All current seroassays using cultured Borrelia burgdorferi as their antigen source have been rendered obsolete by the recombinant OspA Lyme disease vaccine. OspA is the major outer surface protein expressed in cultured B. burgdorferi, and any seroassay that uses whole organisms as its antigen source cannot differentiate between subjects who received the vaccine and those who were naturally infected. We developed a new sensitive and specific enzyme-linked immunosorbent assay (ELISA) utilizing recombinant chimeric borrelia proteins devoid of OspA (rNon-OspA) that can be used to detect antibodies to diagnostically important B. burgdorferi antigens in both OspA-vaccinated and nonvaccinated individuals. We tested sera from patients with Lyme disease and with conditions associated with false-positive serologies, OspA-vaccinated individuals, and healthy high-risk workers from an area of endemicity and normal sera from individuals from areas of nonendemicity. The rNon-OspA test was compared with two commercially available whole-cell immunoassays. The rNon-OspA assay is as sensitive and specific as the whole-cell assay (P > 0.05) for detection of anti-B. burgdorferi antibodies. However, the rNon-OspA assay can differentiate between populations comprised of naturally infected and OspA-vaccinated individuals (P < 0.05). Our data demonstrate that this new sensitive rNon-OspA ELISA can be used for the laboratory detection of B. burgdorferi antibodies regardless of vaccination status and could replace existing serologic assays for Lyme disease.

Prevention of Lyme disease: a review of the evidence

The Healthy People 2010 public health goals targeted a 44% decrease in the incidence of Lyme disease, the most commonly reported tick-borne illness in the United States. To review Lyme disease prevention, clinical trials, epidemiological and experimental studies, and predictive models were evaluated. Geographic distribution of ixodid vectors and local landscape predict Lyme disease risk. Density of infected ticks correlates with incidence and prevalence of Lyme disease, but risk quantitation is made uncertain by tick aggregation and inability to predict tick-human interactions. Outdoor activities are inconsistently or weakly associated with risk, and most infections likely occur in residential areas during routine activities. Tick control (burning or removing vegetation, acaricide use, and deer elimination) reduces Ixodes scapularis populations by up to 94%, and acaricide application to wildlife decreases nymphal I scapularis populations by up to 83%. The effect of these strategies on incidence of Lyme disease in humans is unknown. Studies show that only 40% to 50% of adults take precautions against tick bites even when they are aware of Lyme disease. Effective protection afforded by personal precautions (wearing protective clothing, avoiding ticks, and using insect repellant) has not been shown prospectively. Antimicrobial prophylaxis of tick bites is not warranted. Clinical trials showed vaccines containing recombinant OspA of Borrelia burgdorferi to be efficacious and well tolerated. Currently, vaccination is the only empirically demonstrated method to prevent Lyme disease. The best evidence supports prevention efforts focused on practices that encourage immunization, Lyme disease awareness, and possibly treatment of deer.