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.

Signs and symptoms

Lyme disease can produce a broad range of symptoms. The incubation period is usually one to two weeks, but can be much shorter (days) or much longer (months to years). Lyme symptoms most often occur from May to September in the Northern Hemisphere because the nymphal stage of the tick is responsible for most cases.

Early localized infection Approximately 80% of Lyme infections begin with a rash of some sort at the site of a tick bite, often near skin folds such as the armpit, groin, back of the knee, or the trunk under clothing straps, or in children's hair, ears, or neck. Most people who get infected do not remember seeing a tick or a bite. The rash usually appears one or two weeks (range, 3–32 days) after the bite and expands 2 to 3 cm (0.79 to 1.18 in) per day, reaching a diameter of 5 to 70 cm (2.0 to 27.6 in). The median diameter is 16 cm (6.3 in). The rash is usually circular or oval, red or bluish, and may have a raised or darkened center. This rash is termed an erythema migrans (EM), which translates to "migrating redness." In approximately 79% of cases in Europe, the rash gradually clears from the center toward the edges, possibly forming a "bull's eye" or "target-like" pattern. This clearing happens in only 19% of cases in endemic areas of the United States. The rash may feel warm, usually is not itchy, is rarely tender or painful, and takes up to four weeks to resolve if untreated. The Lyme rash is often accompanied by symptoms of a flu-like illness, including fatigue, headache, body aches, fever, and chills (though usually neither nausea nor upper-respiratory problems). These symptoms may also appear without a rash or linger after the rash has disappeared. Lyme can progress to later stages without a rash or these symptoms. People with high fever for more than two days or whose other symptoms of viral-like illness do not improve despite antibiotic treatment for Lyme disease, or who have abnormally low levels of white or red cells or platelets in the blood, should be investigated for possible coinfection with other tick-borne diseases such as ehrlichiosis and babesiosis. Not everyone with Lyme disease has all the symptoms. Many of these symptoms can also occur with other diseases. This can make obtaining a diagnosis particularly challenging, especially with the rise of co-infection. Asymptomatic infection occurs, but some studies suggest it occurs in fewer than 7% of infected individuals in the United States, compared with about 50–70% of cases in Europe.

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