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Lyme disease is the most commonly reported vector-borne illness in the United States, accounting for more than 95% of such cases. It is caused by the spirochete, Borrelia burgdorferi, which is transmitted to humans through the bite of an Ixodes tick.1,2 Lyme disease is a multisystem, multistage, inflammatory illness.


Since Lyme disease became nationally notifiable in 1991, the annual number of reported cases has more than doubled, with approximately 20,000 new cases reported annually in recent years. More than 90% of the cases of Lyme disease are reported from 10 states located along the northeastern and mid-Atlantic seaboard and in the upper north-central regions of the United States. Sixty-one percent of the reported cases occur in children 5 to 14 years of age.3 The principal risk factor for acquiring Lyme disease in endemic areas is residence in suburban or rural areas that are wooded or overgrown with brush and infested by infected vector ticks. The ticks that can transmit Lyme disease (Ixodes scapularis, also known as the black-legged or deer tick, in the eastern United States, and Ixodes pacificus, also known as the western black-legged tick, in the western United States) are found in wooded areas, high grasses, marshes, gardens, and beach areas. Humans acquire B burgdorferi from infected ticks at the time the tick takes a blood meal.

Lyme disease is not spread by person-to-person contact or by direct contact with infected animals. Although transplacental transmission of B burgdorferi has been reported, the effect of such transmission on the fetus remains uncertain. Available data suggest that congenital Lyme disease occurs only very rarely, if at all.4 Transmission in breast milk has not been documented. Although B burgdorferi can survive in stored blood for several weeks, the risk for transfusion-acquired Lyme disease appears to be minimal.

Clinical Manifestations

The clinical manifestations of Lyme disease depend on the stage of the disease—early, localized disease; early, disseminated disease; or late disease.1,2 The most common manifestation of early, localized Lyme disease, erythema migrans, appears 3 to 30 days (but typically within 7-10 days) after a tick bite at the site of the bite.1,2 Erythema migrans begins as a red macule or papule and usually expands over days to weeks to form a large, annular, erythematous lesion that is at least 5 cm and as much as 70 cm in diameter (median of 15 cm). The rash may be uniformly erythematous, or it may appear as a target lesion with variable degrees of central clearing (eFig. 267.1). It can vary greatly in shape and, occasionally, may have vesicular or necrotic areas in the center. Erythema migrans is usually asymptomatic, but may be pruritic or painful and accompanied by systemic symptoms such as fever, malaise, headache, myalgias, and arthralgias. Patients with early, localized Lyme disease can also present ...

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