Author(s): Paul Mead, David McCormick

Infectious Agent

Lyme disease is caused by spirochetes belonging to the Borrelia burgdorferi sensu lato complex, including B. afzelii, B. burgdorferi sensu stricto, and B. garinii.

Transmission

Borrelia spirochetes are transmitted through the bite of infected 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 might be unaware that they were ever bitten.

Epidemiology

Borrelia transmission has not been documented in the tropics. In Europe, Lyme disease is endemic from southern Scandinavia into the northern Mediterranean countries of Greece, Italy, and Spain, and east from the British Isles into central Russia. Incidence is greatest in central and eastern European countries. In Asia, infected ticks range from western Russia through Mongolia, northeastern China, and into Japan; human infection appears to be uncommon in most of these areas, however. In North America, highly endemic areas include the northeastern and north-central United States.

Lyme disease is occasionally reported in travelers to the United States returning to their home countries. Consider Lyme disease in the differential diagnosis of patients with consistent symptoms and a history of camping, hiking, or outdoor activities. Some case reports describe Lyme disease in Australian and US travelers returning from Europe and endemic regions of the United States, but no data are available regarding the incidence of travel-acquired infection.

Clinical Presentation

The incubation period of Lyme disease 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). Left untreated, infection can progress over several months to cause monoarticular or oligoarticular arthritis, peripheral neuropathy, or rarely, encephalopathy. These long-term sequelae can occur over variable periods of time, ranging from months to years.

Infection with European strains of Borrelia can result in manifestations rarely seen in the United States, specifically lymphocytoma, an acute blister-like lesion, and acrodermatitis chronica atrophicans, characterized by atrophic patches of bluish-red skin that develop over a period of years and typically involve the extremities.

Diagnosis

In people with a history of recent travel to an endemic area (with or without a recollection of a tick bite) a diagnosis of Lyme disease can be made by identifying an EM rash. For patients with evidence of disseminated infection (cardiac, musculoskeletal, neurologic manifestations), serologic testing using commercial assays can aid in diagnosis. Lyme disease is nationally notifiable.

Serological tests used to diagnose domestically acquired Lyme disease might not reliably identify infections acquired internationally. Some laboratories offer testing for additional Borrelia species that cause Lyme disease in Europe but are not found in the United States. These tests are only appropriate for people with a history of travel outside the United States. For diagnostic support, contact the Centers for Disease Control and Prevention (CDC)’s Division of Vector-Borne Diseases (970-221-6400; dvbid@cdc.gov).

Treatment

Most patients can be treated with oral doxycycline, amoxicillin, or cefuroxime axetil; or with intravenous ceftriaxone (See details). Diagnosis and management of disseminated infection can be complicated and may require referral to an infectious disease specialist or rheumatologist.

Prevention

Advise patients to avoid tick habitats (e.g., wooded, brushy, or grassy areas); use an Environmental Protection Agency–registered insect repellent on exposed skin and clothing; and carefully check every day for attached ticks. Instruct patients to minimize areas of exposed skin by wearing long-sleeved shirts, long pants, and closed shoes, and to tuck in shirts and tuck pants into socks to help reduce risk for tick bites (see Sec. 4, Ch. 6, Mosquitoes, Ticks & Other Arthropods).

CDC website: Lyme disease