Lyme disease

Lyme disease, also known as Lyme borreliosis, is a tick-borne disease caused by species of Borrelia bacteria, transmitted by blood-feeding ticks in the genus Ixodes. It is the most common disease spread by ticks in the Northern Hemisphere. Infections are most common in the spring and early summer. Infection is treatable with antibiotics. Most treated patients experience a full recovery. For some patients, recovery may not be immediate or complete, resulting in long-term effects. Early detection and prompt treatment are associated with more favorable outcomes.

The most common sign of infection is an expanding red rash, known as erythema migrans (EM), which appears at the site of the tick bite about a week afterwards. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Other early symptoms may include fever, headaches and tiredness. 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. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, shooting pains or tingling in the arms and legs may develop.

Diagnosis is based on a combination of symptoms, history of tick exposure, and possibly testing for specific antibodies in the blood. If an infection develops, several antibiotics are effective, including doxycycline, amoxicillin and cefuroxime. Standard treatment usually lasts for two or three weeks. People with persistent symptoms after appropriate treatments are said to have post-treatment Lyme disease syndrome (PTLDS).

Prevention includes efforts to prevent tick bites by wearing clothing to cover the arms and legs and using DEET or picaridin-based insect repellents. As of 2026, clinical trials of proposed human vaccines for Lyme disease are being carried out and one is up for regulatory approval, but no vaccine is available. A vaccine, LYMERix, was produced but discontinued in 2002 due to insufficient demand. Several vaccines prevent Lyme disease in dogs.