Lyme Disease: The Great Imitator

Lyme disease (Lyme borreliosis) can be difficult to diagnose when the patient history and presentation fail to provide classic evidence of the disease. Joint pain can be mistaken for rheumatoid arthritis, neurologic signs for multiple sclerosis, and fever and fatigue for influenza or infectious mononucleosis. Lyme disease has therefore been called the "great imitator."

Figure 1. Locations of recogonized Lyme disease worldwide.

Without early diagnosis and treatment, the initial infection may progress to become a multisystem disease associated with significant morbidity. The causative bacterial agents, collectively known as Borrelia burgdorferi sensu lato, actually comprise several closely related species with different antigenic profiles. DPC has developed a qualitative Lyme Antibody Screen* assay for use on its IMMULITE® systems for Lyme disease serology testing. This Lyme disease antibody screening assay uses a variety of antigens derived from European and US Borrelia strains to detect both IgG and IgM to Borrelia in patient sera. For additional, more specific follow-up of positive or equivocal serological test results, DPC offers I.D. Blot Borrelia* immunoblotting tests for the detection of antigen-specific IgG or IgM antibodies.

Transmission and clinical manifestations
Lyme disease is transmitted by the bite of certain deer ticks of the genus Ixodes infected with the spirochete Borrelia burgdorferi sensu lato ("in the broad sense"). Annually, 16,000 cases occur in the US and, on the basis of seroprevalence studies, an estimated 60,000 cases in western and central Europe. The infection may be asymptomatic, may cause only erythema migrans (EM, the classic red bull's-eye rash around the site of the bite), or may cause disseminated disease affecting many organs and tissues. No EM appears in 20 to 40 percent of infected individuals. Diagnosis is easier in endemic areas (Figure 1) when the patient reports having had a tick bite, and disease symptoms include the characteristic EM, along with flulike symptoms, subsequent joint pain and focal neural problems. In patients in nonendemic regions, proper diagnosis is much more difficult. Antibody measurement is therefore a great help in diagnosing the disease.

Disease stages
Lyme disease is divided into three stages that show a certain amount of overlap (Table 1). In stage 1 (early) disease, 3 to 8 weeks after infection, 60 to 80 percent of patients exhibit EM. EM usually subsides within 3 to 4 weeks. In patients who do not exhibit EM, symptoms of the second or third stage may be the first sign of the infection. In stage 2 disease, 2 to 9 months later, the bacteria have spread via the bloodstream and established a multisystem infection with characteristic neurological and myocardial manifestations. Stage 3 disease is characterized by arthritis, acrodermatitis chronica atrophicans (ACA) and neurological manifestations after a long incubation phase of 10 months to 10 years. In ACA, observed almost exclusively in Europe where it is the most common late manifestation of Lyme disease, an initially infiltrative phase of the condition is followed by the atrophic phase: the skin becomes creased, with a thinness reminiscent of cigarette paper, has livid discolorations and exhibits plastic protrusion of vessels.

Serotyping and symptomology
Genetic studies have identified three pathogenic species of the B. burgdorferi sensu lato complex: B. burgdorferi sensu stricto ("strict sense" of B. burgdorferi), B. garinii and B. afzelii. Currently, two serotyping systems based on the outer surface proteins OspA and OspC are well established. Eight OspA and 16 OspC serotypes have been identified on the basis of European and North American isolates' reactivities with sets of monoclonal antibodies specific for these proteins. The heterogeneous antigenic profiles of the different Borrelia species are believed to account for differences in virulence, clinical presentation and epidemiology. Whereas EM may result from infection with any of the three Borrelia species pathogenic for humans, clinical manifestations involving other symptoms show a distinctive geographical pattern. In North America, where B. burgdorferi sensu stricto is the only species isolated, first-stage disease is more pronounced than it is in Europe and includes mainly arthritis. In 60 to 70 percent of US patients, symptoms in addition to EM are seen. In contrast, any of the three pathogenic species may be isolated from European Lyme disease patients, but there appears to be a predominance of B. afzelii isolates from EM and ACA patients, and B. garinii in patient CSF isolates. Early antibiotic treatment can probably prevent Lyme arthritis in many patients. Consequently, prompt diagnosis is of practical importance. Because all three pathogenic species can cause Lyme arthritis, and because different human immune responses to these species are possible, it is important that Lyme disease tests be designed with the differences in various patient populations and geographic regions in mind.

Recommendations for two-step testing and interpretation
Assays for Lyme disease antibodies can provide evidence of previous or current infection; but to improve test reliability, the FDA supports the Centers for Disease Control and Prevention (CDC) recommendation for two-step testing and interpretation of results, as outlined in Figure 2.

Detection of antibodies in serum is dependent on the stage of the disease.

In the first stage, only 40 to 70 percent of patients have detectable antibodies either because EM was overlooked while present and IgM levels have fallen, or because an immune complex prevents the availability of the IgM antibodies. Diagnosis in this stage depends on clinical symptoms. Serology is used to confirm the clinical diagnosis.

Because 60 to 90 percent of the patients with stage 2 or 3 disease have detectable antibodies, serology may be most useful for patients who do not present with EM.

The only exception is treated patients, in whom a serological response is often not seen even if the antimicrobial agent has not eliminated all infecting organisms.

A negative serology result indicates only that there was no serological evidence of infection with B. burgdorferi. It should not be used as the basis for excluding Lyme disease as the cause of illness, especially if the blood was collected within 2 weeks of the onset of symptoms. If Lyme disease is suspected, a second specimen collected 2 to 4 weeks after the first specimen should be tested. If retesting, screening should be performed again; if this result is positive or equivocal, testing should proceed to immunoblotting.

DPC IMMULITE systems Lyme Antibody Screen
The DPC Lyme Antibody Screen, developed for use on the IMMULITE systems, automates initial testing for Lyme disease and offers the features listed below.

Low crossreactivity to potentially interfering antigens present in
	syphilis
	autoimmune disease: SLE, systemic scleroderma
	diseases with polyclonal stimulation: rheumatoid arthritis, infectious mononucleosis (EBV)

DPC I.D. Blot Borrelia
At present, there is no international standardization of Lyme disease serology testing. This can lead to high variability in test results, with both false-negative and false-positive results occurring. For this reason, DPC also offers I.D. Blot Borrelia IgG and IgM-two qualitative tests for additional discrepancy testing. They permit visualization of a patient's unique IgG or IgM antibody response to the various Borrelia antigens. The I.D. Blot Borrelia tests are not restricted by the sensitivity and specificity concerns associated with ELISAs, for which a positive or equivocal result must always be followed with immunoblot confirmation.

Conclusion
DPC's newly developed and evaluated Lyme Antibody Screen and I.D. Blot Borrelia are both sensitive and specific for the detection of Borrelia antibodies. Moreover, the automated Lyme Antibody Screen assay on the IMMULITE family of systems lowers labor and assay costs.

* Under development.