Lyme disease, also known as Lyme borreliosis, is an infectious disease caused by bacteria of the Borrelia type. The most common sign of infection is an expanding area of redness, known as erythema migrans, that begins at the site of a tick bite about a week after it has occurred. The rash is typically neither itchy nor painful. About 25% of people do not develop a rash. Other early symptoms may include fever, headache, and feeling tired. If untreated, symptoms may include loss of the ability to move one or both sides of the face, joint pains, severe headaches with neck stiffness, or heart palpitations, among others. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, people develop shooting pains or tingling in their arms and legs. Despite appropriate treatment, about 10 to 20% of people also develop joint pains, have memory problems, and feel tired much of the time.

Lyme disease is transmitted to humans by the bite of infected ticks of the Ixodes genus. Usually, the tick must be attached for 36 to 48 hours before the bacteria can spread. In North America, the only bacterium involved is Borrelia burgdorferi sensu stricto, while in Europe and Asia, the bacteria Borrelia afzelii and Borrelia garinii are also causes of the disease. The disease does not appear to be transmissible between people, by other animals, or through food. Diagnosis is based upon a combination of symptoms, history of tick exposure, and possibly testing for specific antibodies in the blood. Blood tests are often negative in the early stages of the disease. Testing of individual ticks is not typically useful.

Chronic Lyme disease is a controversial diagnosis that encompasses "a broad array of illnesses or symptom complexes for which there is no reproducible or convincing scientific evidence of any relationship to B. burgdorferi infection." There is no clinical evidence that "chronic" lyme disease is caused by a persistent infection. Most medical authorities advise against long-term antibiotic treatment for Lyme disease.

Background

The Centers for Disease Control and Prevention state that "approximately 10 to 20% of patients treated for Lyme disease with a recommended 2–4 week course of antibiotics will have lingering symptoms of fatigue, pain, or joint and muscle aches. In some cases, these can last for more than 6 months. Although often called 'chronic Lyme disease', this condition is properly known as 'post-treatment Lyme disease syndrome' (PTLDS)". The term is often applied to several different sets of patients. One usage refers to people suffering from the symptoms of untreated and disseminated late-stage Lyme disease: arthritis, peripheral neuropathy and/or encephalomyelitis. The term is also applied to people who have had the disease in the past and some symptoms remain after antibiotic treatment, which is also called post-Lyme disease syndrome. A third and controversial use of the term applies to patients with nonspecific symptoms, such as fatigue, who show no objective evidence they have been infected with Lyme disease in the past, since the standard diagnostic tests for infection are negative.