What Is It?

Lyme disease is an infection caused by bacteria called Borrelia burgdorferi. These bacteria are transmitted through the bites of ticks, primarily the deer tick. Not everyone who develops symptoms of Lyme disease remembers getting bitten by a tick because the deer tick is very small and its bite can go unnoticed.

Lyme disease is most common in the northeastern and midwestern United States. More than 90% of cases have been reported in nine states: Connecticut, Maryland, Massachusetts, Minnesota, New Jersey, New York, Pennsylvania, Rhode Island and Wisconsin. Even within states, there are regions of high risk and others with very low rates of disease. This variation relates to where ticks that carry the bacteria live, breed, and come into contact with humans.

Lyme disease infection recently has caused a great deal of public concern and confusion. Lyme disease is usually not responsible for causing chronic fatigue syndrome or other poorly defined problems. Lyme disease is a distinct illness that causes its own very specific signs and symptoms and can be readily diagnosed. Unexplained medical conditions should not be attributed to Lyme disease simply because no other diagnosis seems likely.

Symptoms

After the tick bite, the first symptom is a rash called erythema migrans (EM), which is usually a flat, reddish rash that spreads from the site of the tick bite. The rash usually is larger than 2 inches wide and can grow larger. It often develops a central clear area known as a bull's eye. The rash usually doesn't itch or hurt. Other symptoms at this stage can include fever, muscle and joint aches, fatigue, headache and a severe stiff neck. In some cases, there are two or more of these well-defined rashes.

Over several days to weeks after the tick bite, Lyme disease can cause neurological problems, including meningitis, which is an infection of the lining of the brain and spinal cord, and Bell's palsy, a weakness in facial muscles caused by nerve injury. Lyme disease also can cause carditis, an inflammation of the heart muscle that can cause irregular heart rhythms with fainting or dizziness. Months to years after Lyme disease affects the heart, changes can be seen on an electrocardiogram (EKG) even when there are no symptoms. Lyme disease also can cause arthritis, either a chronic arthritis that commonly affects one knee or episodes of swelling in several joints, called migratory arthritis.

In later stages of Lyme disease, patients can experience problems with memory and concentration.