Lyme disease.

Lyme disease is a complex multisystem disorder recognized on six continents that is epidemic in some parts of the world during spring, summer, and fall seasons. It is an infectious disease caused by a spirochete, B. burgdorferi, which is transmitted chiefly by I. dammini and pacificus ticks in the United States and I. ricinis in Europe. It is a disease with early and late cutaneous manifestations plus involvement of the nervous system, heart, eye, and joints in variable combinations. 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 with illness greater than 4 to 6 weeks' duration. Although infection is the primary cause, immune mechanisms almost certainly play a synergistic role in some manifestations during late stages. Prompt diagnosis and treatment are important for full recovery. Therapy with doxycycline or amoxicillin is effective in the earliest stages but serious late complications require high doses of intravenous penicillin or ceftriaxone. Some sequelae respond well to antibiotic therapy while others such as chronic arthritis or advanced central nervous system disease may not. Anti-B. burgdorferi antibodies appear to be protective in certain experimental studies but data are limited and inconclusive in humans.