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Lyme Disease

Lyme disease is a tick-borne multisystem infectious syndrome of substantial medical importance and public concern. It is the most frequently reported vector-borne illness in the United States, occurring in 48 of the 50 states at rates of up to 12,000 cases annually. Lyme disease also has been seen on four other continents. Highly endemic regions include the northeastern and upper midwestern regions.

The causative organism, Borrelia burgdorferi, is a flagellated spirochete transmitted from small-mammal reservoirs to humans through bites from infected ticks of Ixodes species (I scapularis in the eastern and upper midwestern United States, I pacificus in California, I ricinus in Europe, and I persulcatus in Asia). Commonly known as deer ticks in the United States and sheep ticks in Europe, these Lyme disease vectors.

Ticks must obtain a blood meal in order to molt and lay eggs, leading to obligatory parasitism of suitable hosts: mammals, reptiles, amphibians, and birds in various locales. Humans become suitable alternative hosts when participating in activities in wooded habitats in areas where ixodid ticks are prevalent. In endemic regions, B burgdorferi moves through enzootic cycles between ticks and reservoir hosts capable of sustaining B burgdorferi infection. Humans are at risk for Lyme disease when exposed to infected ticks questing for a blood meal. In nonendemic regions, immature ticks preferentially parasitize hosts.

Genetic variation in B burgdorferi isolates from different geographic regions may explain observed differences in the clinical manifestations of Lyme disease in Europe and North America. Arthritis is more common in the United States, where all human isolates have belonged to the species B burgdorferi sensu stricto. In parts of Europe, chronic dermatologic manifestations (eg, acrodermatitis chronica atrophicans) are often associated with Borrelia afzelii and some neurologic manifestations (notably meningopolyneuritis, or Bannwarth's syndrome) with Borrelia garinii.

Early disease

The symptoms and signs of Lyme disease are categorized.

Clinical manifestations

The hallmark of early localized Lyme disease is erythema migrans an expanding erythematous patch or ring appearing within 30 days (mean, 9 days) after inoculation of skin with B burgdorferi by an infected tick (figures 1 through 3). According to surveillance criteria from the Centers for Disease Control and Prevention (CDC), the rash must exceed 5 cm in diameter, show expansion, and persist for more than 1 week. The features of the skin lesion that are most suggestive of B burgdorferi infection are expansion.

A minority of patients with erythema migrans report a range of systemic symptoms, including transient chills, fever, myalgias, arthralgias, headache, sore throat, stiff neck, and fatigue within the first month after B burgdorferi infection. Although this spectrum of symptoms has been termed flu-like, respiratory symptoms (cough and sore throat).

Not all cases of Lyme disease present with erythema migrans. In early studies, about one third of patients presented with manifestations of disseminated or late disease.

Laboratory findings

Although visual recognition of erythema migrans is the best indicator of early localized Lyme disease, supportive laboratory data can be helpful in confirming the diagnosis.

Serologic testing is the only routinely available laboratory diagnostic aid for Lyme disease.

A two-step approach involving enzyme-linked immunosorbent assay (ELISA) with subsequent testing of equivocal or positive samples by Western immunoblot technique for specific B burgdorferi antigenic bands can reveal IgM or IgG directed at B burgdorferi.

Although serologic testing is less sensitive in early Lyme disease than in later manifestations it can help clinch the diagnosis in cases in which clinical recognition of erythema migrans is un certain. Laboratory confirmation of B burgdorferi infection may be especially crucial in geographic areas not known to be endemic for Lyme disease, where erythema migrans or similar lesions occur but have not yet been conclusively linked to a specific spirochete or other cause, lime disease.

Disseminated disease

After a period of localized skin infection at the site of inoculation, B burgdorferi infection may spread hematogenously to various target organs. Disseminated Lyme disease occurs 1 to 4 months after an infected tick bite and can include cutaneous, rheumatic, neurologic, and cardiac manifestations." Clinical acumen is required at this stage of illness, because involvement of any of these organ systems may be the first indication of disseminated infection.

The principal cutaneous manifestation of disseminated infection is multiple erythema migrans lesions remote from the original tick bite. These secondary lesions are similar to primary erythema migrans but show less expansion and may be evanescent. B burgdorferi has been cultured from biopsy specimens of secondary skin lesions.