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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.
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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.
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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.
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Clinical Manifestations
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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 ...