appears as a red papule and expands in an annular fashion to at least 5 cm. in diameter

• fatigue, headache, stiffness, myalgia, lymphadenopathy

• neurologic (10 to 15% of patients) and cardiac (6 to 10% of patients) abnormalities may develop weeks to months after lesion

• months to years after onset, swelling and pain in large joints may develop and persist for years ("Lyme arthritis")

DIAGNOSIS

• currently based on clinical findings and serologic tests

• tests are poorly standardized and are insensitive during the first several weeks of infection

INFECTIOUS AGENT

• Borrelia burgdorferi, a spirochete bacterium

MODE OF TRANSMISSION

• bite of an Ixodes tick; transmission does not occur until tick has fed for several hours

• wild rodents (especially the white-footed mouse) and white-tailed deer maintain transmission cycle; tick depends on deer to reproduce and feeds on mice to become infected

• no evidence for person-to-person transmission

• transplacental transmission has been documented

DISTRIBUTION

• in the United States: Atlantic coastal states from Maine to Georgia; upper midwestern states (concentrated in Minnesota and Wisconsin); California and Oregon

• abroad: Europe, Canada, Japan, Australia, China, and the Commonwealth of Independent States

INCUBATION PERIOD

• erythema migrans appears 3 to 32 days after tick exposure

TREATMENT

• oral antibiotics (tetracycline, doxycycline, amoxicillin, erythromycin) for 10 to 30 days

• high-dose intravenous penicillin or ceftriaxone is used if neurologic abnormalities develop

• novel drug regimens are undergoing evaluation