Lyme disease.

Lyme disease is a complex multisystem disorder recognized on three continents, which is epidemic in some regions during spring, summer, and fall seasons. It primarily affects skin, nervous system, heart, and joints. It is an infectious disease caused by a spirochete Borellia burgdorferi, which is transmitted chiefly by Ixodes dammini and pacificus ticks in the United States and Ixodes ricinus in Europe. Diagnosis is based on patient contact with an endemic area, one or more characteristic clinical features, particularly erythema migrans rash, and a positive serologic test for B. burgdorferi infection in the majority of cases. Although infection is the primary cause of the disease, immune mechanisms may play a synergistic role in some manifestations. Prompt diagnosis and treatment are important for full recovery. Treatment with oral tetracycline or penicillin is effective in the earliest stages but late complications require high doses of intravenous penicillin and sometimes corticosteroids. Some late complications are refractory to antibiotic therapy. Antibody appears to be protective in human and experimental studies.