Spirochetes belonging to the Borrelia burgdorferi sensu lato complex, including B. afzelii, B. burgdorferi sensu stricto, and B. garinii.
Through the bite of Ixodes ticks; infected people are often unaware that they have been bitten.
In Europe, endemic from southern Scandinavia into the northern Mediterranean countries of Italy, Spain, and Greece. Incidence is highest in central and Eastern European countries. In North America, highly endemic areas are the northeastern and north-central United States. Transmission has not been documented in the tropics. Lyme disease is rarely reported in returning travelers.
Incubation period is typically 3–30 days. Approximately 80% of people infected with B. burgdorferi develop a characteristic rash, erythema migrans (EM), within 30 days of exposure. EM is a red, expanding rash, with or without central clearing, that is often accompanied by symptoms of fatigue, fever, headache, mild stiff neck, arthralgia, or myalgia. Within days or weeks, infection can spread to other parts of the body, causing more serious neurologic conditions (meningitis, radiculopathy, and facial palsy) or cardiac abnormalities (myocarditis with atrioventricular heart block). Untreated, infection can progress over a period of months to cause monoarticular or oligoarticular arthritis, peripheral neuropathy, or encephalopathy. These long-term sequelae can be typically observed over a number of months, ranging from 1 week to a few years.
Observation of an EM rash with a history of recent travel to an endemic area (with or without history of tick bite) is sufficient. For patients with evidence of disseminated infection (musculoskeletal, neurologic, or cardiac manifestations), 2-tiered serologic testing, consisting of an ELISA/IFA and confirmatory Western blot, is recommended. Patients suspected of acquiring Lyme disease overseas should be tested by using a C6-based ELISA, as other serologic tests may not detect infection with European species of Borrelia.