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Clinical Microbiology Reviews, July 2005, p. 484-509, Vol. 18, No. 3
0893-8512/05/$08.00+0     doi:10.1128/CMR.18.3.484-509.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Diagnosis of Lyme Borreliosis

Departments of Pathology,¹ Microbiology and Immunology,² Medicine, Division of Infectious Diseases, New York Medical College,³ Westchester Medical Center, Valhalla, New York⁴

SUMMARY

INTRODUCTION

CHARACTERISTICS OF B. BURGDORFERI

B. burgdorferi Genospecies

LYME BORRELIOSIS: DISEASE SPECTRUM

LABORATORY DIAGNOSIS

Direct Detection of B. burgdorferi

Culture of B. burgdorferi sensu lato. (i) Culture techniques.

(ii) Culture of clinical specimens.

(iii) Sensitivity of culture.

(iv) Practical considerations.

Molecular methods of detection of B. burgdorferi sensu lato.

(i) PCR analysis of clinical specimens.

(ii) Real-time quantitative PCR.

(iii) PCR sensitivity and specificity.

(iv) Applications and limitations of molecular methods.

Immunologic Diagnosis of B. burgdorferi Sensu Lato Infection

B. burgdorferi sensu lato antigens of importance in immunodiagnosis.

Antibody detection methods.

(i) IFA.

(ii) Enzyme immunoassays.

(iii) Western IB.

(iv) Two-tier testing.

Newer EIA antibody tests.

(i) Enzyme immunoassays using recombinant antigens.

(ii) Peptide-based immunoassays.

(iii) Use of a combination of recombinant or peptide antigens in immunoassays.

Other antibody detection methods. (i) Functional antibodies: borreliacidal antibody assays.

(ii) Detection of antibodies bound to circulating immune complexes.

Detection of antibodies in cerebrospinal fluid.

Cellular immune response in LB: T-lymphocyte and mononuclear cell proliferation assays.

TEST INTERPRETATION

ACKNOWLEDGMENTS

REFERENCES

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INTRODUCTION

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Lyme borreliosis (LB), or Lyme disease, which is transmitted by ticks of the Ixodes ricinus complex, was described as a new entity in the United States in the late 1970s (318, 319, 324, 325). Many of its individual manifestations had been documented many decades earlier in Europe (355). The etiologic agent, Borrelia burgdorferi, was recovered first in 1982 from the vector tick Ixodes dammini (now I. scapularis) (41) and subsequently from skin biopsy, cerebrospinal fluid (CSF), or blood specimens of patients with LB in the United States (22, 323) and Europe (3, 14, 268). In the United States, the Centers for Disease Control and Prevention (CDC) initiated surveillance for LB in 1982, and the Council of State and Territorial Epidemiologists adopted a resolution making LB a nationally notifiable disease in 1990. LB is the most common vector-borne disease in North America and represents a major public health challenge for the medical community. Since 1982, more than 200,000 LB cases in the United States have been reported to the CDC, with about 17,000 cases reported yearly between 1998 and 2001 (54). In 2002 the number of cases of LB in the United States increased to 23,763, with a national incidence of 8.2 cases per 100,000 population. Approximately 95% of the cases occurred in 12 states located in the northeastern, mid-Atlantic, and north central regions (54); these states were Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Wisconsin. LB is widely distributed in European countries and also occurs in far eastern Russia and in some Asian countries (128, 288, 351).

During the past 20 years, notable advances have been made in understanding the etiologic agent, B. burgdorferi, and the illness that it causes. Many excellent reviews have been published detailing progress in expanding the knowledge base on the microbiology of B. burgdorferi (20, 29, 50, 283, 307, 351, 353) and on the ecology and epidemiology (12, 40, 247, 297, 299), pathogenesis (127, 225, 321, 335, 357), clinical aspects (219, 253, 313-316, 372), and laboratory diagnosis (18, 39, 291, 360, 362, 365) of LB. It has been estimated that more than 2.7 million serum samples are tested each year for the presence of B. burgdorferi-specific antibodies in the United States alone (339). To meet the demand for laboratory-based diagnosis, various new tests for direct detection of the etiologic agent, or for detection of specific antibodies by using whole-cell lysates, recombinant antigens, or peptide antigens in enzyme immunoassays (EIA), have been introduced into the clinical laboratory. This review attempts to provide a comprehensive assessment of the development and application of currently available tests for the laboratory diagnosis of LB. Future directions for improvement of established tests and for development of new approaches are also discussed.

CHARACTERISTICS OF B. BURGDORFERI

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B. burgdorferi is a helically shaped bacterium with multiple endoflagella. The cells, configured with 3 to 10 loose coils, are 10 to 30 µm in length and 0.2 to 0.5 µm in width (20). This spirochete possesses several morphological, structural, ecologic, and genomic features that are distinctive among prokaryotes.

Cultured B. burgdorferi organisms are motile and swim in freshly prepared slides. Live organisms can be visualized by dark-field or phase-contrast microscopy. They can also be recognized by light microscopy after staining with silver stains or by fluorescent microscopic methods. The ultrastructure of B. burgdorferi is comprised of an outer slime surface layer (S-layer), a trilaminar outer membrane surrounding the periplasmic space that usually contains 7 to 11 periplasmic flagella and an innermost compartment, the protoplasmic cylinder (120). Detailed information on the cell structure and biology of B. burgdorferi is found in published reviews (20, 353).

B. burgdorferi is the first spirochete whose complete genome was sequenced (98). The genome size of the type strain B. burgdorferi sensu stricto B31 is 1,521,419 bp. This genome consists of a linear chromosome of 910,725 bp, with a G+C content of 28.6%, and 21 plasmids (9 circular and 12 linear) which have a combined size of 610,694 bp (52, 98). Comparative analysis of the genome of the recently sequenced Borrelia garinii strain PBi with that of B. burgdorferi B31 reveals that most of the chromosome is conserved (92.7% identity with regard to both DNA and amino acids) in the two species. The chromosome and two linear plasmids (lp54 and cp26), which carry approximately 860 genes, seem to belong to the basic genome inventory of the Lyme Borrelia species (105). Not all strains of B. burgdorferi have the complete complement of plasmids, and thus the cumulative genome size may vary among different B. burgdorferi isolates.

Genome analysis has revealed that B. burgdorferi possesses certain genetic structures that are uncommon among prokaryotes (98). These include (i) a linear chromosome and multiple linear and circular plasmids in a single bacterium; (ii) a unique organization of the rRNA gene cluster, consisting of a single 16S rRNA gene (rrs) and tandemly repeated 23S (rrl) and 5S (rrf) rRNA genes; (iii) over 150 lipoprotein-encoding genes, which account for 4.9% of the chromosomal genes and 14.5% of the plasmid genes, significantly higher than that of any other bacterial genome sequenced to date; (iv) a substantial fraction of plasmid DNA that appears to be in a state of evolutionary decay; (v) evidence for numerous, potentially recent DNA rearrangements among the plasmid genes; and (vi) a lack of recognized genes that encode enzymes required for synthesis of amino acids, fatty acids, enzyme cofactors, and nucleotides. B. burgdorferi also lacks genes coding for tricarboxylic acid cycle enzymes or for compounds involved in electron transport, findings which, taken together with the preceding, indicate the parasitic nature of this microorganism (52, 98, 353).

At least three B. burgdorferi sensu lato species, i.e., B. burgdorferi sensu stricto, B. garinii, and B. afzelii, are pathogenic to humans in Europe (342, 351). In contrast, B. burgdorferi sensu stricto is the sole species known to cause human infection in the United States (195). However, several subtypes of B. burgdorferi sensu stricto have been identified (175, 176), and an association between specific subtypes of B. burgdorferi sensu stricto and hematogenous dissemination and invasion in patients (304, 370) and experimentally infected animals (348, 349) has been reported.

Of the seven B. burgdorferi sensu lato species identified in Asia, only B. garinii and B. afzelii have been confirmed definitively to be pathogenic in humans. Although studies with both patients and laboratory animals have indicated the potential for B. bissettii, B. valaisiana, or B. lusitaniae to cause clinical disease (65, 81, 106, 257, 334), the pathogenicity of these Borrelia species in humans is not well established.

The genetic relatedness of B. burgdorferi sensu lato isolates has been compared at the species, subspecies, or single gene level by various molecular approaches. Earlier analyses of B. burgdorferi sensu lato isolates representing different species suggested that these species had highly conserved chromosomal gene orders (51, 232) with linear plasmid profiles similar to that described for the B. burgdorferi sensu stricto type strain B31 (243). Recent studies, however, have documented genetic heterogeneity among B. burgdorferi sensu lato isolates in the United States (173, 195) and in Europe (263, 288, 352). A large number of DNA sequences of B. burgdorferi sensu lato genes are now available in the GenBank database from the National Center for Biotechnology Information (http://www.ncbi.nlm.nih.gov/entrez/). Examples include fla, vlsE, bmpA, and dbpA and genes encoding B. burgdorferi sensu lato 16S rRNA and outer surface proteins A and C.

It is well known that B. burgdorferi sensu lato expresses different surface proteins in adaptation to various microenvironments (79, 95, 299). For example, the spirochete expresses OspA but not OspC when residing in the midguts of unfed ticks. However, during a blood meal by the tick, some spirochetes stop expressing OspA and instead express OspC (230, 298). Certain B. burgdorferi sensu lato genes either are expressed only in a mammalian host or have significantly up-regulated expression in that environment; such gene products include VlsE (71, 230), DbpA (71, 129), BBK32 (96), Erp (202), and Mlp (376) proteins. Recently, whole-genome microarrays were employed to analyze gene expression of B. burgdorferi sensu stricto grown under conditions analogous to those found in unfed ticks, fed ticks, and mammalian hosts (32, 220, 231, 278). Gene expression analysis of B. burgdorferi B31 grown at 23°C and 35°C, to simulate temperatures found in tick vectors and mammalian hosts, respectively, demonstrated that a total of 215 open reading frames were differentially expressed at the two temperatures. Strikingly, 136 (63%) of the differentially expressed genes were plasmid carried, which highlights the potential importance of plasmid-carried genes in the adjustment of B. burgdorferi sensu lato to diverse environmental conditions (231).

Genetic diversity and differential expression of B. burgdorferi sensu lato genes in patients have important implications for development of molecular assays and serologic tests in the laboratory diagnosis of LB. As discussed in the following sections, the choice of PCR primers targeting different segments of the B. burgdorferi sensu lato genome, as well as the selection of particular antigens for serologic assays, may affect the sensitivities and specificities of these diagnostic assays (252, 291).

LYME BORRELIOSIS: DISEASE SPECTRUM

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Infection with B. burgdorferi sensu lato can result in dermatological, neurological, cardiac, and musculoskeletal disorders. The basic clinical spectra of the disease are similar worldwide, although differences in clinical manifestations between LB occurring in Europe and North America are well documented (219, 316, 351). Such differences are attributed to differences in B. burgdorferi sensu lato species causing LB on the two continents. Furthermore, differences in clinical presentations exist between regions of Europe, presumably due to differences in the rates of occurrence of infection caused by distinct B. burgdorferi sensu lato species (128, 288, 342).

Patients with B. burgdorferi sensu lato infection may experience one or more clinical syndromes of early or late LB. Usually, early infection consists of localized erythema migrans (EM), which may be followed within days or weeks by clinical evidence of disseminated infection that may affect the skin, nervous system, heart, or joints and subsequently, within months, by late infection (219, 314, 316, 318, 373). Arthritis appears to be more frequent in North American patients (326, 332), whereas lymphocytoma, acrodermatitis chronica atrophicans (ACA), and encephalomyelitis have been seen primarily in Europe (313).

EM is the characteristic sign of early infection with B. burgdorferi sensu lato and the clinical hallmark of LB. In recent series it is recognized in at least 80% of patients with objective clinical evidence of B. burgdorferi sensu lato infection who meet the CDC surveillance definition of LB (327). The rash begins at the site of the tick bite as a red macule or papule, rapidly enlarges, and sometimes develops central clearing. The clinical diagnosis of early LB with EM relies on recognition of the characteristic appearance of a skin lesion of at least 5 cm in diameter. At this stage, patients may either be asymptomatic or, more commonly in the United States, experience flu-like symptoms, such as headache, myalgia, arthralgias, or fever (309, 332). The presence of constitutional signs and symptoms in a patient with EM has been considered evidence of dissemination by some investigators, but this is not evidence based (192). Instead, we will refer to this clinical presentation as symptomatic EM later in this review.

Hematogenous dissemination of B. burgdorferi sensu lato to the nervous system, joints, heart, or other skin areas, and occasionally to other organs, may give rise to a wide spectrum of clinical manifestations of what is called early LB. Usually, patients with objective evidence of dissemination experience one or more of the following syndromes: multiple EM lesions, atrioventricular conduction defects, myopericarditis, arthritis, facial palsy, meningitis, and meningoradiculoneuritis (Bannwarth's syndrome) (238, 333, 343).

Late LB may develop among some untreated patients months to a few years after tick-transmitted infection. The major manifestations of late LB include arthritis, late neuroborreliosis (peripheral neuropathy or encephalomyelitis), and ACA. Lyme arthritis begins as intermittent attacks of mono- or pauciarticular arthritis, especially of large joints. In up to 10% of patients, arthritis may persist for months or a few years despite treatment with antimicrobials. Treatment-resistant arthritis is more frequently seen in patients with the certain HLA DRB alleles (112, 145). It has been suggested that autoimmunity plays a role in this clinical entity (320, 338).

While Lyme arthritis is the most common late manifestation of LB in North America, ACA appears to be the most common manifestation of late LB in Europe. As mentioned earlier, these differences are likely due to the different species causing LB in the two continents (219, 316, 351).

More details on the clinical spectra of LB are found in recent reviews (219, 313, 314, 316, 372).

LABORATORY DIAGNOSIS

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Four different approaches have been used in the clinical laboratory: microscope-based assays, detection of B. burgdorferi-specific proteins or nucleic acids, and culture. Of these, culture of B. burgdorferi sensu lato undoubtedly offers the best confirmation of active infection and has been increasingly used as a diagnostic modality by many researchers on both sides of the Atlantic. The availability of cultured organisms has also allowed investigation of the structural, molecular, antigenic, and pathogenetic properties of the different B. burgdorferi sensu lato species.

Direct microscopic detection of B. burgdorferi sensu lato has limited clinical utility in laboratory confirmation of LB due to the sparseness of organisms in clinical samples (24, 27, 75-77, 125, 139, 153, 156, 190, 212, 221, 310). Antigen detection assays (aside from PCR) also suffer from the same limitations as microscopic detection. Although antigen capture tests have been used to detect B. burgdorferi sensu lato antigens in CSF of patients with neuroborreliosis (67, 69) and in urine samples from patients with suspected LB (83, 131, 155), their reliability is poor or at best questionable (155). Our review of direct methods of detection of B. burgdorferi sensu lato in clinical samples will focus on culture and molecular methods.

Culture of B. burgdorferi sensu lato. (i) Culture techniques. The liquid media currently used to grow B. burgdorferi sensu lato were derived from the original Kelly medium (152) through various modifications made over time (17, 19, 267, 328, 329). Current versions of this medium (Barbour-Stoenner-Kelly II medium [BSK II] [17], BSK-H [262], and Kelly medium Preac-Mursic [MKP] [267]) are better able to support growth of B. burgdorferi sensu lato in terms of recovery from low inocula, shorter generation times of the spirochete, and maximal concentration of spirochetes in culture (10⁸ to 10⁹/ml) (Table 1). Key ingredients of BSK II include CMRL-1066, which is a standard medium used for growing various types of mammalian cells; bovine serum albumin fraction V, which serves as a rich source of protein and to stabilize the pH; N-acetylglucosamine, a precursor for bacterial cell wall biosynthesis; rabbit serum; citrate; pyruvate; and many others.

Cultures in liquid medium are usually incubated at 30° to 34°C under microaerophilic conditions. Incubation at temperatures of 39°C or higher may reduce or prevent growth (17). Cultures are incubated for up to 12 weeks, which is much longer than is necessary to grow most other human bacterial pathogens, due in part to the spirochete's prolonged generation time (7 to 20 h or longer) during log-phase growth (17, 266, 353). Detection of growth is accomplished by periodic examination of an aliquot of culture supernatant for the presence of spirochetes by dark-field microscopy or by fluorescence microscopy after staining with the fluorochrome dye acridine orange or a specific fluorescence-labeled antibody (277, 367). Visualized spirochete-like structures should be confirmed as B. burgdorferi sensu lato by demonstration of reactivity with specific monoclonal antibodies or by detection of specific DNA sequences by using PCR methodology (215, 312, 353, 367). Lack of experience in the microscopic detection of B. burgdorferi sensu lato can lead to false-positive readings, as other structures such as cellular debris may appear thread-like and thus be mistaken for B. burgdorferi sensu lato (110).

B. burgdorferi sensu lato can also be grown on solid media with agarose to solidify the liquid media discussed above and incubated under microaerophilic or anaerobic conditions (17, 158, 266). An advantage of using solid media is that individual colonies can be identified as a means to select out particular clonal strains of B. burgdorferi sensu lato.

Laboratory-propagated strains of B. burgdorferi sensu lato can be successfully cocultivated with tick cell lines (157, 213, 229) and with certain mammalian cell lines (121, 311, 341). Cocultivation techniques may prove to be useful for primary isolation of B. burgdorferi sensu lato from clinical specimens as well (311, 341).

(ii) Culture of clinical specimens. B. burgdorferi sensu lato can be recovered from various tissues and body fluids of patients with LB, including biopsy (14, 25, 31, 140, 165, 178, 200, 204, 209, 214, 221, 227, 237, 256, 267, 303, 327, 333, 342, 369) and lavage (369) specimens of EM skin lesions, biopsy specimens of ACA skin lesions (14, 258, 267, 342), biopsy specimens of borrelial lymphocytoma skin lesions (188), cerebrospinal fluid specimens (60, 147, 237, 267, 342), and blood specimens (13, 22, 189, 216, 221, 322, 367, 368, 374). Anecdotally, recovery of B. burgdorferi sensu lato from other tissue or fluid specimens (189), such as synovial fluid (289), cardiac tissue (312), and iris (265), has also been reported.

Aside from the late cutaneous manifestation ACA, from which B. burgdorferi sensu lato has been recovered more than 10 years after onset of the skin lesion (14), the vast majority of successful isolations have been from untreated patients with early disease (EM or early neuroborreliosis) (147, 219, 303, 351, 360).

(a) Erythema migrans. Recovery of B. burgdorferi sensu lato from 2- to 4-mm skin biopsy samples of an EM skin lesion can typically be achieved for at least 40% of untreated patients (Table 2). The highest reported success rates were 86% in a study of 21 U.S. patients for whom 4-mm skin biopsy specimens were cultured (25) and 88% in a study from The Netherlands of 57 patients who underwent a 4-mm skin biopsy (342). B. burgdorferi sensu lato can be recovered from both primary (site of tick bite) and secondary (presumed to arise by hematogenous dissemination) EM lesions (204, 213). Despite the clinical tradition of biopsying the advancing border of an EM lesion, a recent systematic study of this question conducted in Europe found comparable yields from biopsy specimens taken from the EM center (140). According to one report, positive cultures can also be obtained from clinically normal-appearing skin 4 mm beyond the EM border (25).

Recovery of B. burgdorferi sensu stricto from solitary EM lesions is significantly more likely in U.S. patients with skin lesions of shorter duration (214), suggesting that the patient's immune response is usually effective in clearing the spirochete from that skin site over a relatively short time interval. Consistent with this premise are the results of a recent study in which the number of spirochetes in 2-mm skin biopsy samples of the advancing border of an EM skin lesion was determined using a quantitative PCR (qPCR) technique (177). This study demonstrated that significantly fewer spirochetes were present in older or larger EM lesions (in the United States the size of an EM lesion correlates directly with its duration) (23, 214, 215). The same phenomenon probably explains a much earlier clinical observation that in the absence of antibiotic therapy, EM lesions will nevertheless resolve in a median time period of approximately 4 weeks (317). Clearance of spirochetes from the skin in the absence of antibiotic treatment has also been documented in a rhesus macaque model of B. burgdorferi sensu stricto infection (254).

Borrelia burgdorferi sensu stricto usually cannot be recovered on culture of EM lesions of patients already receiving appropriate antibiotic treatment (372) and rarely, if ever, cannot be recovered from the prior site of a resolved EM lesion in U.S. patients who have completed a course of appropriate antimicrobial therapy (26, 214). Borrelia burgdorferi sensu stricto has been recovered, however, from cultures of EM lesions of patients treated with the narrow-spectrum cephalosporin cephalexin, an antibiotic which is inactive in vitro against B. burgdorferi sensu lato and ineffective clinically (4, 226).

(b) Whole blood, serum, and plasma. The rate of recovery of B. burgdorferi sensu stricto from blood or blood components of untreated patients with EM had generally been 5% or less (22, 108, 323, 345), and until recently this source of culture material was largely abandoned. In past studies on the sensitivity of blood cultures for recovery of B. burgdorferi sensu stricto, only a very small volume of less than 1 ml of blood or blood components was cultured (22, 108, 216, 217, 322, 323, 345). For other bacterial infections, however, the volume of blood cultured is an important determinant of yield (201, 354, 356). The reason for this is that with more conventional pathogens the number of cultivable bacteria per milliliter of whole blood is less than 1 in 50% of bacteremic patients and less than 0.1 in nearly 20% (82, 151). Therefore, in view of the recommendation to culture quantities of blood as large as 20 to 30 ml for other bacterial infections, the rationale for culturing much smaller volumes for LB patients was open to challenge.

In a series of recent experiments with adult patients with EM from the United States, it was demonstrated that recovery of B. burgdorferi sensu stricto was better from serum than from an identical volume of whole blood (374) and that the yield from plasma was significantly greater than that from serum (367). Yield directly correlated with the volume of material cultured. Recovery of B. burgdorferi sensu stricto from high-volume cultures of 9 ml of plasma inoculated into a modified BSK II preparation devoid of antimicrobials and gelatin, with a 20:1 ratio of medium to plasma, was consistently above 40% (367, 368). Unfortunately, high-volume plasma cultures are not appropriate for young children, since obtaining such a large quantity of blood would be unacceptable. Reported rates of recovery from blood of patients with EM in Europe have been <10% (13, 189). This may be due to a low frequency of hematogenous dissemination of B. afzelii, the principal cause of EM in Europe (351), or to culturing an inadequate volume of blood.

A study that addressed further increasing the volume of plasma from 9 ml to 18 ml for adult U.S. patients with EM found only a small increment of approximately 10% in culture yield (368), suggesting that if substantially greater yields from blood cultures are still possible, it will be by further modifying the culture medium rather than by increasing the volume of plasma cultured. In that study it was estimated that the average number of cultivable B. burgdorferi sensu stricto cells per milliliter of whole blood was approximately 0.1, which, if correct, would explain why blood cultures had such a consistently low yield in former studies in which the volume of blood or blood components cultured was extremely small (368).

A recent study of patients with EM showed a greater recovery of B. burgdorferi sensu stricto from blood of symptomatic patients; nevertheless, the majority of symptomatic patients had negative blood cultures (371), raising doubts about the reliability of the assumption that the presence of symptoms indicates dissemination.

Although less extensively studied, culture of blood samples is rarely positive in patients with any objective clinical manifestation of LB other than EM (191, 216; J. Nowakowski, unpublished observations). Blood cultures are also negative in patients with persistent subjective symptoms following completion of an appropriate course of antibiotic treatment (154, 191).

(iii) Sensitivity of culture. Although a number of as low as one spirochete can be recovered on culture using laboratory-adapted and continuously propagated strains of B. burgdorferi sensu stricto (17, 254, 262, 331), the sensitivity of culture for clinical specimens is undefined. Compared to PCR for detection of spirochetes in cutaneous specimens, culture has proven to be slightly more sensitive in some studies but not in others (31, 165, 209, 227, 256, 303, 327, 380). Such disparate results are likely to be attributable to differences in the various studies in the PCR protocols employed, including type of PCR and/or primer and target selection and/or method of tissue preservation, as well as differences in culture techniques, including size of the skin biopsy sample cultured and/or choice of culture medium. In a recent U.S. study of skin biopsy samples of 47 untreated adult patients with EM lesions, culture grew B. burgdorferi sensu stricto in 51%, compared with an 81% detection rate using a qPCR method (P = 0.004 by Fisher's exact test, two tailed) and a 64% detection rate using a nested PCR (P = 0.3) (227).

Although all of the different B. burgdorferi sensu lato species and subspecies recognized to cause human infection can be cultivated, it is not clear whether the sensitivity of culture is identical for each. In one study, subtyping of B. burgdorferi sensu stricto was performed directly on 51 skin biopsy samples of patients with EM by using PCR-restriction fragment length polymorphism of the 16S-23S rRNA gene intergenic spacer region and also on the strains of B. burgdorferi sensu stricto that grew from culture of the same biopsy samples (176). No significant difference in the rate of recovery of any single subtype was observed. However, due to the relatively small number of isolates of B. burgdorferi sensu stricto in that study, further investigation of this question is needed.

(iv) Practical considerations. Culture has been principally used as a diagnostic modality in research studies and has enabled a better understanding of the clinical, laboratory, and pathogenetic aspects of LB through identification of a group of culture-authenticated patients (7, 215, 309, 332, 333). For example, the recognition that substantive differences exist in the clinical manifestations of patients with EM caused by B. burgdorferi sensu stricto compared with those with EM caused by B. afzelii was based on analysis of culture-confirmed cases (332). In addition, culturing of ticks, EM skin lesions, and blood samples was instrumental in demonstrating that different subtypes of B. burgdorferi sensu stricto vary in their potential to spread to extracutaneous sites (304, 370). Patients with culture-confirmed LB have also been a valuable source of specimens to assess the accuracy of other diagnostic tests (7, 203). Such well-defined patient populations have also played an important role in studying therapeutic regimens (375) and vaccines (327).

Culture, however, has not been used in routine clinical practice as a diagnostic test for several reasons. One reason has been the lack of consistent availability of high-quality (i.e., borrelial growth-promoting) lots of liquid medium for growing B. burgdorferi sensu lato. Until fairly recently, this medium was not sold commercially, and although BSK-H is now available commercially, it has periodically been in short supply or of variable quality.

Furthermore, by most conventional bacteriologic standards, borrelial cultures are more labor-intensive, more expensive, and much slower, requiring up to 12 weeks of incubation before being considered negative. The rapidity of identifying a positive culture, however, is directly dependent on the frequency with which the culture supernatant is examined microscopically, since macroscopic changes in the appearance of the culture medium tend to occur later, if at all. In our research studies, in which B. burgdorferi sensu stricto cultures are usually first examined only at 2 weeks, 70% of positive cultures of skin biopsy samples of EM lesions and approximately 85% of positive cultures of plasma from EM patients turned positive at 2 weeks, and approximately 95% of each type of sample turned positive by 4 weeks (G. P. Wormser, unpublished observations). The time to detection of a positive specimen can be reduced to a clinically relevant time frame if cultures are examined on a daily basis (203). For example, the Marshfield Laboratories identified 74 (82%) of 90 positive cultures within the first 7 days of incubation and 32 (35%) within the first 3 days (277). In the experience of that laboratory, the longest time to detection of a positive culture was 16 days. Culture positivity might be detected even more quickly if aliquots of culture supernatant were examined by PCR, rather than microscopy, to detect B. burgdorferi sensu lato DNA (301), and in the future it is conceivable that such an approach might be adaptable to automation.

Another limiting factor is that culture is useful only for untreated patients. Culture positivity is rapidly aborted by even a few doses of appropriate antibiotic treatment (214, 303).

Perhaps the most fundamental limitation is that culture is far too insensitive in patients with extracutaneous manifestations of LB, which is unfortunately the group of patients who pose the greatest diagnostic confusion (219, 314). Culture has been most successful for patients with early LB who have EM, but visual recognition of the characteristic appearance of the skin lesion is usually sufficient for an accurate diagnosis, and no laboratory testing is indicated (218, 219). Culture would be helpful only in a minority of cases in which the rash may be atypical or the patient was not known to have had tick exposure in an area where LB is endemic.

Molecular methods of detection of B. burgdorferi sensu lato. For laboratory diagnosis of LB, the utilization of molecular techniques has focused mainly on PCR-based methods. The first PCR assay for specific detection of a chromosomally encoded B. burgdorferi sensu lato gene was reported in 1989 (282). Various other PCR protocols were subsequently developed for detection of B. burgdorferi sensu lato DNA in clinical specimens and were reviewed by Schmidt in 1997 (291).

(i) PCR analysis of clinical specimens. Given that the number of spirochetes in infected tissues or body fluids of patients is very low, appropriate procedures for sample collection and transport and preparation of DNA from clinical samples are critical for yielding reliable and consistent PCR results. A variety of clinical specimens from patients with suspected Lyme disease have been analyzed by PCR assays (291). Of these, skin biopsy samples taken from patients with EM or ACA have been the most frequently tested specimens (346). Depending on the clinical manifestations of the patients, appropriate body fluid samples (e.g., blood, CSF, or synovial fluid) can be collected and analyzed by PCR.

The sensitivity of PCR assays may be reduced by degradation of the B. burgdorferi sensu lato DNA during sample transport, storage, and processing. If the tissue is kept in BSK medium for over 24 h, some spirochetes will have migrated from the skin biopsy to the culture medium. In this case, DNA should be prepared from both the skin biopsy and the medium and analyzed by PCR separately. Comparative analysis using a quantitative PCR assay of skin biopsy specimens placed in BSK overnight to 2 days (177) has demonstrated a higher copy number of B. burgdorferi sensu stricto DNA in samples extracted from the medium than in those extracted from the skin sample. This may be attributed to migration of the spirochetes out of the skin sample and/or to the presence of PCR inhibitors in skin (G. Wang, unpublished data). Alternatively, spirochetes that have migrated into the medium can be collected by centrifugation and subjected to DNA extraction together with the biopsy tissue.

Clinical specimens collected from patients should be subjected to DNA extraction and PCR analysis shortly after collection, or they should be kept frozen. Studies on infected animal tissues suggest that PCR with DNA prepared from fresh frozen tissues has higher yields than that with DNA from paraffin-embedded, formalin-fixed tissues (163).

As host DNA can interfere with PCR detection of B. burgdorferi sensu lato in clinical and tick samples (62, 302), an optimized DNA extraction procedure is essential to yield reliable PCR results for certain clinical samples (28). Also, PCR inhibitors may be present in various biological samples (blood, urine, synovial fluid, and CSF) obtained from patients (31); this can usually be assessed by spiking negative samples with a known number of spirochetes or particular amounts of spirochetal DNA during DNA extraction or PCR amplification. In most cases, inhibition of PCR may be minimized by dilution of the extracted DNA (62).

PCR results can be qualitative (conventional PCR and nested PCR) or quantitative (competitive PCR and real-time PCR). Each of these PCR methods has its advantages and disadvantages. For laboratory diagnosis of B. burgdorferi sensu lato infection, a qualitative PCR is usually sufficient. Nevertheless, several real-time PCR instruments such as the Sequence Detection System (Applied Biosystems, Inc.) and LightCycler (Roche Diagnostics, Inc.) are now commercially available and offer options for automation in a clinical laboratory setting (90).

The efficiency of a PCR assay is determined by several factors. Among these, the selections of an appropriate gene target and primer set for PCR amplification are the most important in development of any new PCR protocols. In general, a PCR primer set yielding an amplicon of 100 to 300 bp is recommended, as it has high amplification efficiency under standard PCR conditions and can reduce the effects of DNA fragmentation during sample processing. Although PCR assays targeting numerous B. burgdorferi sensu lato genes have been employed in research laboratories, only a few of these genes have been utilized by clinical laboratories as targets for PCR analysis of B. burgdorferi sensu lato DNA in clinical specimens. These include chromosomally carried genes such as rRNA genes, flaB, recA, and p66 and the plasmid-carried gene ospA (291).

(a) PCR analysis of skin biopsy samples from patients with cutaneous manifestations. B. burgdorferi sensu lato DNA was first detected by PCR in skin biopsies from three of four patients with EM and four of five patients with ACA in The Netherlands in 1991 (199). In 1992, Schwartz et al. reported on the detection of B. burgdorferi-specific rRNA genes in skin biopsies from EM patients in the United States (303).

PCR targets that have been employed for detection of B. burgdorferi sensu lato DNA in skin biopsy specimens include p66 (31, 210, 211, 344, 358, 359), the 16S rRNA gene (296, 303), fla (177, 234, 256), the 23S rRNA gene (31), the 5S rRNA-23S rRNA gene spacer (279), recA (177), and ospA (209, 279, 327).

The sensitivity of PCR for detection of B. burgdorferi sensu lato DNA in EM lesions is usually high, ranging from 36% to 88% (Table 3). A prospective study in the United States showed that 85 of 132 (64%) skin biopsies taken from EM patients during a phase III vaccine trial were positive by PCR (327). B. burgdorferi sensu lato-specific DNA has been detected in 54 to 100% of skin biopsy samples from patients with ACA in Europe (Table 3). The sensitivity of PCR for detection of B. burgdorferi sensu lato in skin biopsy samples from ACA patients appears to be dependent on the target sequences selected. Rijpkema et al. reported that 15 of 24 (63%) skin biopsies from patients with ACA in The Netherlands were positive by a nested PCR targeting ospA; only 10 of these samples (42%) were positive if a fragment of the 5S-23S rRNA gene intergenic spacer was targeted (279). Results also depended on which genes were used as targets in PCR for skin biopsies from ACA patients in a small study reported from Germany. Four of five patients with ACA were detected by PCR targeting the p66 gene, versus two of five when the 23S rRNA gene was amplified (31).

In general, the sensitivity of PCR for detection of B. burgdorferi sensu lato DNA in blood, plasma, or serum samples from patients with Lyme disease is low (Table 3). The low yield could be a reflection of lack of spirochetemia or transient spirochetemia (22), a low level of spirochetes in blood (108), and/or the presence of PCR inhibitors in host blood (2, 62, 345).

In one study, PCR-documented spirochetemia in patients with EM was correlated with symptomatic illness and with the presence of multiple EM lesions (108); multivariate analysis indicated that a high number of systemic symptoms was the strongest independent predictor of PCR positivity (108).

None of 78 patients with post-Lyme disease syndromes (musculoskeletal pains, neurocognitive symptoms, dysesthesia, fatigue, malaise, headache, or sleep disturbance) had detectable DNA in blood specimens, despite a positive Western immunoblot (IB) for immunoglobulin G (IgG) antibodies against B. burgdorferi sensu stricto in 39 of these patients (154).

(c) PCR analysis of CSF specimens from patients with neuroborreliosis. B. burgdorferi sensu lato DNA has been detected by PCR in CSF specimens from patients with a variety of neurological symptoms in the United States and in Europe (Table 3). Lack of a gold standard method to support the diagnosis of neuroborreliosis makes it difficult to assess the performance of PCR with CSF.

The sensitivity of PCR for detection of B. burgdorferi sensu lato DNA in CSF specimens may be dependent on the clinical presentation, CSF white cell counts, disease duration, and whether antibiotic treatment was given. In a study of 60 U.S. patients with neuroborreliosis (16 with early and 44 with late neuroborreliosis), the sensitivity of PCR in CSF was 38% in early and 25% in late neuroborreliosis, and an inverse correlation was found between duration of antimicrobial treatment and PCR results (223). In this study, four different PCR primer or probe sets were used, three targeting OspA genes and one targeting OspB genes, and concordance between the different assays was poor. In a Swedish study, B. burgdorferi sensu lato DNA was detectable only in LB patients with CSF pleocytosis (7/36; 19.4%). None of 29 patients with clinical signs of LB (EM, cranial neuritis, or radiculoneuritis) without CSF pleocytosis was positive by PCR analysis of CSF specimens (236). Another study found that 7 of 14 (50%) neuroborreliosis patients from Denmark with disease duration of less than 2 weeks yielded a positive PCR result, compared with only 2 of 16 (13%) patients in whom the illness duration was greater than 2 weeks (P = 0.045) (165).

(d) PCR analysis of synovial fluid from patients with Lyme arthritis. PCR analysis of synovial fluid is a much more sensitive approach than culture for detection of B. burgdorferi sensu lato in affected joints of patients with Lyme arthritis (30, 87, 133, 172, 224, 252, 270).

In a U.S. study of 88 patients, B. burgdorferi sensu stricto DNA was detected in synovial fluid of 75 (85%) patients with Lyme arthritis (224). The PCR positivity rate was lower in patients who had received antibiotic therapy than in untreated patients. Of 73 patients who were untreated or treated with only short courses of oral antibiotics, 70 (96%) had a positive PCR in synovial fluid samples. In contrast, B. burgdorferi sensu stricto DNA was demonstrated in only 7 of 19 (37%) patients who received either parenteral antibiotics or oral antibiotics for more than 1 month (224). Four PCR primer sets were used in this study, three amplifying DNA sequences encoding OspA and one targeting a portion of the gene encoding 16S rRNA. Among the 75 patients with positive PCR results, the most sensitive primer-probe set detected B. burgdorferi sensu stricto DNA in 89%, versus 56% for the least sensitive set. Only 48 of the 75 (64%) patients with a positive PCR result were positive with all three OspA primers (224). Therefore, the yield of PCR to detect B. burgdorferi sensu lato DNA in synovial samples will depend on the primer-probe set (s) used and the duration of antimicrobial therapy. It is noteworthy that B. burgdorferi DNA has been detected in synovial membrane samples of patients whose synovial fluid specimens were PCR negative after antibiotic treatment (269).

The observation of higher sensitivity of PCR targeting B. burgdorferi sensu stricto plasmid-encoded OspA than of that targeting the 16S rRNA chromosomally encoded genes in synovial fluid specimens (224, 252) has been referred to as "target imbalance." It has been speculated that B. burgdorferi sensu stricto present in the synovium may selectively shed OspA DNA segments into the synovial fluid.

(e) PCR analysis of urine samples from patients with early Lyme borreliosis. B. burgdorferi sensu lato has been frequently recovered from culture of urinary bladder specimens of experimentally infected laboratory animals (21, 348), suggesting that this spirochete could be excreted into the urine. However, although there have been reports of detection of B. burgdorferi DNA by PCR in urine specimens from patients with EM (28, 164, 290, 292), with neuroborreliosis (130, 146, 164, 172, 187, 270), or with Lyme arthritis (109, 146, 270), the sensitivity was highly variable. In addition, nonspecific amplification in urine PCR using different targets has been documented (31, 146, 172, 290). Thus, it is not appropriate to use urine PCR for the laboratory diagnosis of LB.

(ii) Real-time quantitative PCR. A real-time PCR assay was first used for quantitation of B. burgdorferi DNA in tissues from experimentally infected laboratory mice (208, 242). Subsequently, it has been employed to analyze the number of spirochetes in field mice (33, 349), dogs (330), field-collected or laboratory-infected tick vectors (103, 260, 347), and clinical specimens of patients with LB (177, 296; reviewed in reference 346). Also, real-time PCR assays have been utilized to genotype the pathogenic B. burgdorferi sensu lato species in both ticks and EM patients in Europe (207, 261, 276). In addition, real-time multiplex PCR assay has been applied for simultaneous detection of B. burgdorferi sensu stricto and Anaplasma phagocytophilum infections in ticks (66).

Recently, the number of spirochetes in clinical specimens of patients with LB was determined by real-time qPCR assays (177, 296). In one study, B. burgdorferi sensu stricto-specific recA DNA was detected by a LightCycler qPCR assay in 40 (80%) skin biopsy samples from 50 untreated adult U.S. patients with EM (177). The number of spirochetes in a 2-mm biopsy ranged from 10 to 11,000, with a mean number of 2,462 spirochetes. Significantly higher numbers of spirochetes were detected in culture-positive than in culture-negative skin specimens (3,940 versus. 1,642 spirochetes; P < 0.01). In another study, B. burgdorferi sensu lato fla was detected using a TaqMan probe in 5 of 28 (17.9%) synovial fluid specimens and 1 of 5 (20%) synovial membrane biopsies obtained from 31 patients with arthropathies in Switzerland (296). The numbers of spirochetes varied from 20 to 41,000/ml of synovial fluid. Of 56 CSF samples from 54 patients with a clinical suspicion of neuroborreliosis, only one (1.8%) was positive by real-time PCR (296). It is not clear whether these CSF specimens were simultaneously analyzed by conventional PCR or any other molecular assays.

(iii) PCR sensitivity and specificity. Table 3 summarizes the sensitivities and specificities of PCR assays for the detection of B. burgdorferi DNA in different clinical samples as published in MEDLINE-indexed periodicals during the years 1991 to 2003. Of the 24 studies in which B. burgdorferi sensu lato DNA in skin biopsies was examined, the sensitivities of the PCR assays varied from 36 to 88% for patients with EM and from 54 to 100% for patients with ACA. The median sensitivities of the reported PCR assays for detection of B. burgdorferi DNA in skin biopsies from patients with EM and ACA were 69% and 76%, respectively. The sensitivity of PCR assays for detection of B. burgdorferi sensu lato in whole blood (plasma or serum) and CSF specimens is low (Table 3). By contrast, higher PCR sensitivities were reported in both U.S. and European studies with synovial fluid samples from patients with Lyme arthritis.

A published meta-analysis also demonstrated that PCR is a very sensitive approach when it is employed to detect B. burgdorferi sensu lato DNA in skin biopsy and synovial fluid specimens from patients with LB, whereas the diagnostic value of PCR assays for detection of B. burgdorferi sensu lato DNA in blood (plasma or serum) and CSF specimens is low (85).

(iv) Applications and limitations of molecular methods. PCR-based molecular techniques have been employed for (i) confirmation of the clinical diagnosis of suspected LB, (ii) molecular species identification and/or typing of the infecting spirochetes in clinical specimens or on cultured isolates, and (iii) detection of coinfection of B. burgdorferi sensu lato and other tick-borne pathogens. However, PCR assays have not been widely accepted for laboratory diagnosis of LB because of low sensitivity in CSF and blood. PCR as a diagnostic tool may be hampered by potential false-positive results due to accidental contamination of samples with a small quantity of target DNA. False-positive PCR results have been reported for LB (206).

Although PCR is highly sensitive for detection of B. burgdorferi sensu lato DNA in skin biopsy samples from patients with EM (85), such testing is rarely necessary, as a clinical diagnosis can be easily made if the characteristic skin lesion is present. For patients with LB involving systems other than skin, PCR sensitivity is in general low, with the exception of patients with Lyme arthritis.

Due to limitations in direct detection of B. burgdorferi sensu lato in clinical specimens, antibody detection methods have been the main laboratory modality used to support a clinical diagnosis of LB. Although a cellular immune response is also elicited, most methods used in the laboratory confirmation of LB involve detection of serum antibodies. It is, however, important to emphasize that relatively few studies have evaluated serologic tests in culture-confirmed populations. Therefore, conclusions derived from published studies on the serology of patients with clinically defined Lyme borreliosis, discussed later in this review, have inherent limitations.

B. burgdorferi sensu lato antigens of importance in immunodiagnosis. It is important to understand the antigenic composition of B. burgdorferi sensu lato, as it pertains to immunodiagnosis. Numerous early studies recognized the importance of the flagellar protein flagellin (41 kDa), or FlaB, as an immunodominant antigen (63, 70). Strong IgG and IgM responses to this protein are developed within a few days after infection with B. burgdorferi sensu lato (8, 84, 111). Thus, some immunoassays consist of purified flagella alone (114, 115, 138, 148), whereas in others, flagellin is added to enrich the antigenic mixture (174). Unfortunately, although highly immunogenic, this antigen is highly cross-reactive with antigens in other bacteria, particularly when denatured, as in immunoblots (35, 91, 179). Certain flagellin epitopes are also cross-reactive with antigens found in mammalian tissues such as neural tissues, synovium, and myocardial muscle (1, 179). The internal portion of the flagellin molecule, containing the variable, genus-specific immunodominant domain, is less cross-reactive with antigens of other bacteria than the whole protein (101, 179, 274). The flagellar outer sheath protein FlaA, with a molecular size of 37 kDa, is another immunodominant antigen, especially in early disease (7, 84, 104, 246).

One of the most immunodominant antigens early after infection with B. burgdorferi sensu lato is the plasmid-encoded OspC protein (molecular size of about 21 to 25 kDa) (8, 84, 89, 241, 363), which begins to be expressed during tick feeding while the spirochete is still in the tick midgut. Highly passaged in vitro-cultured B. burgdorferi sensu lato does not express OspC, which explains why the importance of this antigen was unrecognized in early studies that used high-passage B. burgdorferi sensu lato as the source of antigen (63, 70). OspC is heterogeneous, and amino acid differences exist among the sequences of OspC proteins from the different B. burgdorferi sensu lato species (135, 197, 336). Furthermore, intraspecies differences also exist; for example, at least 13 OspC serotypes have been identified in B. garinii by using a panel of monoclonal antibodies (361). Sixty-nine ospC groups have been described among B. burgdorferi sensu lato species isolated from different sources in Europe and United States when assayed using the technique of single-strand conformational polymorphism (159). Of interest is that invasive B. burgdorferi sensu lato strains appear to belong to just 24 of the 69 ospC groups (159). It is postulated that OspC is an important virulence factor for both infectivity and invasiveness of B. burgdorferi sensu lato species (86, 193, 304). Antibodies elicited against OspC may be borreliacidal and thus may play a role in the functional antibody assays described below. The search for immunogenic, conserved epitopes within the OspC protein has led to the development of a synthetic peptide that contains the conserved C-terminal 10 amino acids of OspC (pepC10) (198).

The chromosomally encoded 39-kDa protein BmpA (306) is also immunogenic. The gene encoding this protein is located in a bmp cluster that also includes genes for BmpB, BmpC, and BmpD; all have molecular sizes similar to that of BmpA (271). However, it is unclear if BmpB through -D have any utility as antigens in serologic assays. Genetic and antigenic differences have been found among BmpA sequences of different B. burgdorferi sensu lato species, which may limit the use of this antigen in serologic testing (281).

Decorin binding protein A (DbpA) (also referred to as Osp17), which has a molecular size of approximately 17 kDa, is immunogenic (124, 136). DbpA is associated with binding of B. burgdorferi sensu lato to the host collagen-associated proteoglycan decorin. Similar to the case for other B. burgdorferi sensu lato proteins, considerable differences in amino acid sequences exist among DbpA proteins of different B. burgdorferi sensu lato species.

Neither OspA (31 kDa) nor OspB (34 kDa) is significantly expressed by B. burgdorferi sensu lato during early stages of infection. OspA is down-regulated in the tick midgut during tick feeding (298, 299). Presumably OspA and OspB are eventually expressed in mammals, since antibodies to these antigens can be detected during late infection (10, 84). Antibodies to OspA or OspB may be borreliacidal (46, 132, 286, 287). OspA antibodies were readily generated after administration of the recombinant OspA vaccine, which was commercially available in the United States for use in humans until March 2002 (327).

Recently, the Vmp-like sequence expressed (VlsE) protein, a surface-exposed lipoprotein encoded by the linear plasmid lp28-1 of B. burgdorferi B31, has been found to be highly immunogenic (378). Antigenic variation in B. burgdorferi sensu lato occurs when recombination between silent vls cassettes and vlsE takes place. VlsE in B. burgdorferi sensu lato has a predicted molecular mass of approximately 34 to 35 kDa and contains variable and invariable domains. Studies on the antigenicity of this protein demonstrated that one invariable region (IR6), which is found within the variable portion of VlsE, is highly immunogenic (161, 170). This sequence is conserved among B. burgdorferi sensu lato species, making it an appealing candidate as a broadly reactive immunodominant antigen.

Several other antigens expressed in vivo in the mammalian host appear promising in the search for highly specific immunodominant antigens. Among these are the P35/BBK32 and P37 proteins (10, 94, 96). BBK32 is a fibronectin binding protein first described as P35 in a form lacking some of its N-terminal amino acids; it has an apparent molecular mass of about 47 kDa (96). The in vivo-expressed P35/BBK32 and P37 proteins are not equivalent to other B. burgdorferi sensu lato proteins of diagnostic significance of similar size, such as VlsE, FlaA, or the P35 scored by Engstrom et al. in their immunoblot evaluation (89). Expression of P37 or P35/BBK32 by B. burgdorferi sensu lato in clinical materials, as well as in ticks during a blood meal, has supported their presence in the early stages of infection (80, 96).

Antibody detection methods. Several methods have been used for detection of antibodies to B. burgdorferi sensu lato. Early modalities included indirect immunofluorescent-antibody assays (IFA) and a variation of this assay using antigens attached to a membrane (FIAX) (251). These assays have for the most part been replaced by EIA, including enzyme-linked immunosorbent assay (ELISA) and enzyme-linked fluorescent assay (ELFA), that are more amenable to automation (366). Additional immunoassays in use are Western IBs and immunochromatographic and dot blot assays. Methods less frequently used are assays that detect borreliacidal (functional) antibodies, antibodies bound to immune complexes (IC), and hemagglutinating antibodies (46, 48, 248, 287).

At least 70 different commercial immunoassays to detect B. burgdorferi sensu stricto antibodies have been approved for use in the United States by the Food and drug Administration (FDA) (6, 55). Several of these assays are sold under a label different from that under which they were originally marketed, and others are no longer available. Most of these assays use the B31 type strain of B. burgdorferi sensu stricto as the source of antigen. Other strains of B. burgdorferi sensu stricto have been used in assays developed by academic centers in the United States, and various B. burgdorferi sensu lato species have been employed in in-house or commercial assays available in Europe.

(i) IFA. IFA uses cultured organisms fixed onto glass slides. Serum specimens are diluted in preparations that may include an absorbent such as material derived from Reiter treponema or egg yolk sac to remove nonspecific antibodies. After addition of fluorescein isothiocyanate-labeled anti-human IgG or IgM, the presence of antibodies is detected by fluorescence microscopy. Specimens testing reactive at screening dilutions are serially diluted, and titers of 128 or 256 for IgM or IgG, respectively, are usually considered positive (186, 284). Limitations of this assay include the need for fluorescence microscopy and for well-trained personnel and the subjectivity in reading and interpreting fluorescence microscopy. These issues were addressed in the modification of this assay that was available about a decade ago (FIAX; Whittaker), which used antigens applied to membranes, with the degree of fluorescence read by an automated system.

(ii) Enzyme immunoassays. ELISA is the most frequently used format to test for antibodies to B. burgdorferi sensu lato. Most commonly, antigen mixtures comprised of whole-cell sonicates of B. burgdorferi sensu lato are used as the source of antigen for the detection of IgG, IgM, or IgA antibodies individually or in combination (most frequently IgG-IgM combinations). Purified antigens, such as flagellar components, or recombinant antigens, such as P39, have been added to the antigen mixture in some kits (6). Recently, an ELISA using only a single synthetic peptide derived from the VlsE sequence (IR6 or C6 peptide) as the source of antigen has become commercially available.

Using sonicated whole-cell preparations of low-passage B. burgdorferi sensu lato, the sensitivity of ELISA is in general less than 50% in acute-phase sera of patients with EM of a duration of less than 1 week. Sensitivity increases rapidly over time after the first week in untreated patients with EM. Sensitivity is also high in patients with EM who are symptomatic or who have multiple EMs. Sensitivity is very high in patients with objective evidence of extracutaneous involvement (e.g., carditis or neuroborreliosis) (84). ELISA is almost invariably positive in sera of patients with late disease such as arthritis (Table 4) (84).

Whole-cell antigen preparations lack specificity because of the presence of cross-reacting antigens of B. burgdorferi sensu lato. These include common bacterial antigens such as heat shock proteins, flagellar antigens, and others (35, 64, 89, 91). Specificity is also affected by the choice of absorbent material used to dilute the serum specimens. Sera of individuals who received OspA vaccination may react in ELISA using whole-cell sonicates (9). Although the commercial availability of the vaccine has been discontinued, some previously vaccinated individuals may still have antibodies reacting with OspA. Specificity is in general better with substitution of selected recombinant or peptide antigens for whole-cell sonicates.

ELISA has advantages over other immunoassays, including ease of testing, objective generation of numerical values that correlate in relative terms with the quantity of antibodies present, and the capability of automation. Due to lack of specificity of ELISA and other first-tier assays, such as ELFA or IFA, using whole-cell antigen preparations, a positive test is not indicative of seropositivity. A recent analysis of results obtained with an automated ELFA found that the specificity was 91% for 559 samples from a control population (137). Serum specimens testing positive or equivocal with a sensitive ELISA, ELFA, or IFA should be retested with IB; this approach is termed two-tier testing (53). First-tier assays should detect both IgG and IgM antibodies to B. burgdorferi sensu stricto, and separate IgG and IgM IBs should be done as the second tier.

(iii) Western IB. The use of antigens separated by molecular size in IB assays has contributed to the determination of which antigens of B. burgdorferi sensu lato are immunodominant at different stages of LB. Academic centers in the United States have evaluated in-house IB assays using B. burgdorferi sensu stricto strains other than B31 (84, 89). The few commercial IB assays that are currently available in the United States use B. burgdorferi sensu stricto strains; two manufacturers use B31 (6). Various B. burgdorferi sensu lato species and strains isolated from different geographic locations have been studied in Europe (117, 118, 280). Based on recognized inter- and intraspecies differences among the immunodominant antigens of B. burgdorferi sensu lato, it is not surprising that the source of antigens in IB affects the detection of antibodies in European patients with LB (280).

Whether B. burgdorferi sensu lato antigens elicit IgM versus IgG antibodies depends on the duration of infection and the manifestation of LB. Detection of reactivity is also affected by the quality of the antigen used in the immunoassays (including the type and source of antigen). In early LB, IgM antibodies are directed to OspC and the flagellar antigens, FlaB (41 kDa) and FlaA (37 kDa) (7) (Fig. 1, left). Variable rates of IgM response to BmpA (39 kDa) have been observed in sera of patients with early LB, which appears to be related in part to the source of antigen used and/or the duration of disease prior to testing for antibodies (7, 84, 89, 181). The highest rates for IgM reactivity to the 39-kDa protein were reported by Engstrom et al. (89), using B. burgdorferi sensu stricto strain 297 (84%), and by Ma et al. (181), using B31 (50%). In contrast, Dressler et al. (84), using B. burgdorferi sensu stricto strain G39/40, reported IgM reactivity to the 39-kDa protein in only 4 and 8% of acute- and convalescent-phase sera of patients with EM, respectively. The infrequency of reactivity to BmpA antigen reported by Dressler et al. could be attributed to the low expression of this antigen by the B. burgdorferi sensu stricto G39/40 strain used in their study. We have observed IgM reactivity to this antigen in only 3% of acute-phase sera of patients with E