Lyme disease is an infection resulting from the bacteria, Borrelia burgdorferi, which enter the body when certain infected ticks bite. There are three stages of infection.
In the early localized stage, a rash, called erythema migrans, appears at the site of the tick bite from three days to a few weeks later. The rash starts as a small red mark and over days slowly grows to at least two inches wide. It can spread to 10 or more inches, sometimes with a ring or bull’s-eye shape.
Most often, the rash does not hurt or itch. About 10 – 25% of the time, the rash where the tick bit goes unnoticed. If left untreated, the infection may spread to other parts of the body in days to weeks. This is called the early disseminated stage. The person infected may have many signs and symptoms, including:
- More than one rash
- Fever
- Joint pain and muscle pain
- Headache
In about 20% of cases, the infection can attack the nervous system. This can cause very bad headache and stiff neck, paralysis of the muscles of the face or painful inflammation of nerves. If the infection reaches the heart, as it does in about 5% of cases at this stage, the heartbeat may slow too much (known as heart block). Some people will have no symptoms.
The late stage may occur months to even years after the bite, mostly in those who did not get early treatment. At this stage, the infection can affect the joints (Lyme arthritis), causing pain and swelling of one or both knees. Less often, Lyme arthritis can involve other, mostly large, joints.
Late-stage infection rarely can also harm the nervous system. It may affect the peripheral nerves (nerves outside the brain and spinal cord), leading to numbness or tingling or, less often weakness. If the infection affects the brain, it may lead to trouble with memory and concentration.