Lyme Disease

Lyme Disease, bacterial disease transmitted to people by ticks. Lyme disease is caused by a spiral-shaped bacterium known as Borrelia burgdorferi. This bacterium is frequently carried by ticks of the genus Ixodes, primarily the deer tick (also known as the black-legged tick) and the related Western black-legged tick. Immature ticks become infected by feeding on small rodents, such as the white-footed mouse, and other mammals that are infected with the bacteria.

Early symptoms of Lyme disease include a red, circular, smooth rash that expands in size and may resemble a bull's-eye. The rash is painless, does not itch, and may disappear on its own. Several days to several weeks after infection, an infected person may develop flulike symptoms such as fever, headache, a stiff neck, joint and muscle pain, and severe fatigue.

Doctors often treat patients early in the disease solely on the basis of their symptoms and if they have had a known or likely exposure to infected ticks. In the later stage of disease, blood tests are available that measure the body's antibody response against the Borrelia burgdorferi bacteria. These tests are unreliable if used within four weeks of infection because antibody levels may be too low to be detected. Tests designed to detect the presence of the bacterium itself are under development.

Physicians treat Lyme disease with antibiotics. Most patients in the early stages of Lyme disease respond well after two to four weeks of medication. Patients may have persistent fatigue and achiness after treatment, but these symptoms generally resolve within six months. Patients in a later stage of the disease with more severe symptoms may require treatment with one or more intravenous antibiotics for up to six weeks. People in the later stage of the disease typically respond slowly to antibiotic treatment and some people may continue to suffer from symptoms for years.