Borrelia burgdorferi, the causative agent of Lyme disease, is a fastidious microaerophilic spirochete. The human infection Lyme borreliosis is caused primarily by three pathogenic genospecies: B. burgdorferi sensu stricto (hereafter referred to as B. burgdorferi), Borrelia garinii, and Borrelia afzelii.
- B. burgdorferi is the sole cause of Lyme borreliosis in the United States; all three genospecies are found in Europe, and the latter two species occur in Asia.
- Lyme disease is the most common vector-borne illness in the United States, with ∼300,000 cases each year.
- Ixodes ticks transmit the disease.
- I. scapularis, which also transmits babesiosis and anaplasmosis, is found in northeastern and midwestern states; I. pacificus is found in western states.
- The white-footed mouse is the preferred host for larval and nymphal I. scapularis. Adult ticks prefer the white-tailed deer as host.
- Nymphal ticks transmit the disease to humans during the early summer months after feeding for ≥24 h.
Lyme disease usually begins with erythema migrans (EM; stage 1, localized infection) before disseminating (stage 2) or causing persistent infection (stage 3).
- Stage 1 (localized infection): After an incubation period of 3-32 days, EM develops at the site of the tick bite (commonly the thigh, groin, or axilla) in 80% of pts.
- The classic presentation is a red macule that expands slowly to form an annular lesion with a bright red outer border and central clearing. Central erythema, induration, necrosis, vesicular changes, or many red rings within an outer ring are also possible.
- Most pts do not remember the preceding tick bite.
- Stage 2 (disseminated infection): Given that some pts do not notice EM, many pts present within days or weeks after infection with secondary annular skin lesions, nonspecific systemic signs and symptoms, neurologic deficits, or cardiac manifestations due to hematogenous spread.
- Nonspecific signs and symptoms include severe headache, mild neck stiffness, fever, chills, migratory musculoskeletal pain, arthralgias, malaise, and fatigue. These manifestations subside within a few weeks, even in untreated pts.
- Neurologic deficits occur in ∼15% of pts and may include meningitis; encephalitis; cranial neuritis, including bilateral facial palsy; motor or sensory radiculoneuropathy; mononeuritis multiplex; ataxia; or myelitis. Lymphocytic pleocytosis (∼100 cells/µL) is found in CSF, often along with elevated protein levels and normal or slightly low glucose concentrations.
- Cardiac involvement occurs in ∼8% of pts. Atrioventricular (AV) block of fluctuating degree is most common, but acute myopericarditis is possible. Cardiac involvement usually lasts for only a few weeks but may recur in untreated pts.
- Stage 3 (persistent infection): Of untreated pts in the United States, ∼60% develop frank arthritis, usually consisting of intermittent attacks of oligoarticular arthritis in large joints (especially the knees) that last for weeks or months.
- Joint-fluid cell counts range from 500 to 110,000/µL (average, 25,000/µL); the majority of the cells are neutrophils.
- Arthritis can persist despite eradication of spirochetes, potentially due to infection-induced autoimmunity or retained spirochetal antigens.
- Chronic neurologic involvement (e.g., subtle encephalopathy affecting memory, mood, or sleep; peripheral neuropathy) is less common. In Europe, severe encephalomyelitis is seen with B. garinii infection.
- Acrodermatitis chronica atrophicans, a late skin manifestation, is seen in Europe and Asia and is associated with B. afzelii infection.
- Post-Lyme syndrome: For months or years afterward, ∼10% of pts have subjective pain, neurocognitive manifestations, or fatigue symptoms-a syndrome indistinguishable from chronic fatigue syndrome and fibromyalgia. There is no evidence that these symptoms are caused by active infection.
Serologic evidence combined with a compatible clinical picture is the usual basis for diagnosis.
- Only 20-30% of pts have positive serologic results in acute-phase samples, whereas 70-80% have positive results in convalescent-phase samples obtained 2-4 weeks later. Of note, serologic tests do not discriminate between active and past disease as both IgM and IgG may persist for years after treatment.
- Serologic analysis consisting of a two-step approach (ELISA screening with western blot confirmation for cases with positive or equivocal results) is recommended only for pts with at least an intermediate pretest likelihood of having Lyme disease.
- IgM and IgG testing should be done in the first 2 months of illness, after which IgG testing alone is adequate.
- CDC-adopted criteria dictate that the IgM western blot must show at least 2 of 3 defined bands and that the IgG western blot must show at least 5 of 10 defined bands to be considered positive.
- PCR is most useful for joint fluid, is less sensitive for CSF, and has little or no utility for plasma or urine.
- Although culture of the organism is possible, it is reserved primarily for research settings.
| TREATMENT | ||
Lyme Borreliosis
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The risk of infection with B. burgdorferi after a recognized tick bite is so low that antibiotic prophylaxis is not routinely indicated. However, if an attached, engorged I. scapularis nymph is found or if follow-up will be difficult, a single 200-mg dose of doxycycline, given within 72 h of the tick bite, effectively prevents the disease.