Lyme disease is caused by infection with the spirochete, Borrelia burgdorferi (Bb). The infection is spread by ticks, which defecate the organism into the skin after a blood meal. The disease is usually demarcated into three clinical phases -- early localized (days to a month after the tick bite), early disseminated (two weeks to 10 months after the tick bite) and late (months to years after the tick bite).

The early localized phase is characterized by a unique skin rash, erythema migrans and a viremic syndrome consisting of myalgias, arthralgias, fatigue, stiff neck and headache. The early disseminated phase is characterized by cardiac abnormalities, including conduction disturbances or myopericarditis and neurologic abnormalities, including acute meningitis or encephalitis, cranial and peripheral neuropathies, and rheumatic abnormalities in the form of episodic polyarthritis and arthralgias. In 25% of 50% of patients, the early disseminated phase is not preceded by recognized erythema migrans. The late phase consists of arthritis, CNS symptoms, such as changes in memory and cognition, and fibromyalgia-like symptoms.

Not all patients, even if untreated, develop all or most of these symptoms. There are many patients who convert from seronegativity to seropositivity without any recognized clinical symptoms. Most of the manifestations of the disease, but not the fibromyalgia syndrome, can be successfully treated with a number of antibiotic regimens, including doxycycline, amoxicillin and ceftriaxone. A vaccine, which induces the production of antibodies to an outer surface protein on Bb (Osp A), has recently been introduced and appears to be 80% effective after a series of three immunizations over a 12-month period. The clinical features of Lyme disease have been the subject of several recent reviews and will be the subject of another Cyberounds^® conference.

Diagnosis

The diagnosis of Lyme disease can be confirmed by serological testing, a two-step procedure in which serum is tested for antibody reactivity to a crude extract of whole Bb, using an ELISA assay. The ELISA test is sensitive for Lyme disease (ca 95% during the early disseminated and late phases of the disease) but is not entirely specific, since infections with other spirochetes, such as T. pallidum (syphilis), as well as spirochetal infections of the mouth, may induce antibodies which cross react with the antigens used in the ELISA test. Positive Bb ELISA tests may also be seen in conditions associated with a polyclonal antibody response, such as HIV infection or systemic lupus erythematosus. Therefore, if this test is positive, then the specificity of the antibodies for Bb antigens must be confirmed by immunoblotting, looking for either IgG or IgM antibodies to Bb antigens with specific molecular weights. During the early phases of infection, the IgM test is usually positive, while during the later phases the IgG test is almost always positive. The test remains positive for many years, though the pattern of antibody reactivity may vary, and also remains positive after successful treatment of the infection.

In the remainder of this conference, I address four questions frequently asked by clinicians concerning the laboratory diagnosis of Lyme disease:

1. How reliable are the current laboratory tests for Lyme disease?
2. What is the effect of the Lyme vaccine on antibody testing for Lyme disease?
3. Is testing for antibodies to Bb in CSF of help in the diagnosis of the disease?

How Reliable Are the Current Laboratory Tests for Lyme Disease?

The original method for detecting antibodies to Bb was an indirect immunofluorescent assay in which sera were incubated with Bb organisms that had been affixed to microscope slides. Because of technical reasons, this assay was difficult to standardize and was found to be poorly reproducible from laboratory to laboratory. With the newer ELISA methods, using lysates of Bb as antigenic substrate, along with the confirmatory immunoblot tests, there is excellent reproducibility. In a proficiency assay, in which blinded specimens from patients with well characterized and established Lyme disease, together with normal control patients, were sent to 80 licensed clinical laboratories, there was a greater than 95% agreement among the laboratories. Thus, there is no benefit in sending a patient's serum to more than one reputable laboratory.

These results cannot be extended to office testing, where much more variability has been encountered. In a recently study, there was much lower agreement among laboratories who tested sera from early phase patients. In such patients, the current serologic tests for Lyme disease appear to be less reliable and many experts feel that treatment decisions should instead rely on the level of clinical suspicion.

Can the Antibody Test Be Negative in Bb Infected Patients?

During the early localized phase of Lyme disease and the first one to two weeks of the early disseminated phase of the infection, the titer of IgM antibodies may be too low to detect with the routine ELISA methodology. Depending on the prevalence of Bb in the tick population in the area, the physician may want to treat such patients "prophylactically" to allay patient anxiety, although the cost effectiveness of such treatment has not been proven. In one study, from an endemic area for Lyme disease, a large number of patients presenting with tick bites, who tested negative serologically, were followed prospectively without antibiotic treatment. None of the patients developed Lyme disease. On the other hand, patients with erythema migrans after a tick bite in an endemic area (i.e., Lyme disease) may occasionally fail to mount a positive antibody response after treatment with antibiotics. A few of these patients may develop late manifestations of Lyme infection without a history of recurrent tick bites.

What Is the Effect of the Lyme Baccine on Serologic Testing for Lyme Disease?

The vaccine contains the 30Kda OspA protein of Bb as the principal immunogen and vaccinated individuals mount high titers of antibodies to this antigen. The currently available ELISA test for Bb uses lysates of organisms that contain large amounts of OspA protein and cannot distinguish between infected and vaccinated individuals. Confirmation of specific antibody response with the immunoblot test is also more difficult after vaccination. Reactivities against OspA proteins and breakdown products of OspA proteins may obscure the presence of other specific bands. Thus, the vaccine will add to the cost of screening for Lyme disease, which can still occur in vacinees and will diminish the accuracy of the serologic tests.

Two approaches have been proposed to remedy this problem. In one approach, a mutant Borrelia organism has been developed which lacks OspA. The antigen lysate from these organisms do not react with the sera from vaccinated individuals. In the other, a test for borreliacidal antibodies has been developed. These antibodies are not found in vacinees. Neither of these assays has received FDA approval and both will add significantly to the cost of serological screening

Is Testing for Antibodies to Bb in CSF Useful in the Diagnosis of Lyme Disease?

Lyme disease can involve the central and peripheral nervous system. It has been suggested that when the infection is present in the CNS, there is local production of antibodies, which can be detected in the CSF by the ELISA test. Local production of antibody, rather than diffusion of antibody into the CSF from serum, has been postulated, based on an increased ratio of Lyme IgG antibody to total IgG in the CSF, compared to a similar ratio in the patient's serum. This number has been referred to as the CSF Lyme index. However, most centers for Lyme disease have abandoned this index because of its lack of clinical correlation.

More recently, a very sensitive CSF antigen-capture ELISA and immunoblot method has been reported as useful in discriminating between patients with CNS Lyme disease and patients with other neurologic conditions in a group of patients who came from a region endemic for Lyme disease. This method is currently not available on a routine basis. The use of PCR on CSF for Bb, as an alternate method for detecting local CNS, has not yet proven to be reliable. Thus, at the present time, the diagnosis of CNS Lyme infection by serological testing is very problematic.