Spirochetes belonging to the Borrelia burgdorferi sensu lato complex, including B. afzelii, B. burgdorferi sensu stricto, and B. garinii.
Through the bite of Ixodes (blacklegged) ticks, typically, immature (nymphal) ticks. Nymphal ticks are small, about the size of a poppy seed, and elude easy detection. Patients with Lyme disease may be unaware that they had ever been bitten.
In Europe, Lyme is endemic from southern Scandinavia into the northern Mediterranean countries of Italy, Spain, and Greece and east from the British Isles into central Russia. Incidence is highest in central and Eastern European countries.
In Asia, infected ticks range from western Russia through Mongolia, northeastern China, and into Japan; however, human infection appears to be uncommon in most of these areas. 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 occasionally reported in travelers to the United States returning to their home countries; it should be considered in the differential diagnosis of those with consistent symptoms and a history of hiking or camping.
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, 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 observed to occur over variable periods of time, 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 becoming infected with Lyme disease while traveling overseas should be tested by using a C6-based ELISA, as other serologic tests may not detect infection with European species of Borrelia. Lyme disease is nationally notifiable.
Most patients can be treated with oral doxycycline, amoxicillin, or cefuroxime axetil or with intravenous ceftriaxone (see www.cdc.gov/lyme). Diagnosis and management of disseminated infection can be complicated and usually requires referral to an infectious disease, rheumatologist, or other specialist.
Avoid tick habitats, use insect repellent on exposed skin and clothing, and carefully check every day for attached ticks. Minimize areas of exposed skin by wearing long-sleeved shirts, long pants, and closed shoes; tucking shirts in and tucking pants into socks can help reduce risk (see Chapter 3, Mosquitoes, Ticks & Other Arthropods).