Lyme disease, also known as Lyme borreliosis, is an infectious disease caused by a bacterium named Borrelia spread by ticks. The most common sign of infection is an expanding area of redness on the skin, known as erythema migrans, that appears at the site of the tick bite about a week after it occurred. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Other early symptoms may include fever, headache 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, 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 develop joint pains, memory problems, and tiredness for at least six months.
Lyme disease is transmitted to humans by the bites of infected ticks of the genus Ixodes. In the United States, ticks of concern are usually of the Ixodes scapularis type, and must be attached for at least 36 hours before the bacteria can spread. In Europe ticks of the Ixodes ricinus type may spread the bacteria more quickly. In North America, Borrelia burgdorferi and Borrelia mayonii are the cause. 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.
Prevention includes efforts to prevent tick bites such as by wearing clothing to cover the arms and legs, and using DEET-based insect repellents. Using pesticides to reduce tick numbers may also be effective. Ticks can be removed using tweezers. If the removed tick was full of blood, a single dose of doxycycline may be used to prevent development of infection, but is not generally recommended since development of infection is rare. If an infection develops, a number of antibiotics are effective, including doxycycline, amoxicillin, and cefuroxime. Standard treatment usually lasts for two or three weeks. Some people develop a fever and muscle and joint pains from treatment which may last for one or two days. In those who develop persistent symptoms, long-term antibiotic therapy has not been found to be useful.
Lyme disease is the most common disease spread by ticks in the Northern Hemisphere. It is estimated to affect 300,000 people a year in the United States and 65,000 people a year in Europe. Infections are most common in the spring and early summer. Lyme disease was diagnosed as a separate condition for the first time in 1975 in Old Lyme, Connecticut. It was originally mistaken for juvenile rheumatoid arthritis. The bacterium involved was first described in 1981 by Willy Burgdorfer. Chronic symptoms following treatment are well described and are known as post-treatment Lyme disease syndrome (PTLDS). PTLDS is different from chronic Lyme disease; a term no longer supported by the scientific community and used in different ways by different groups. Some healthcare providers claim that PTLDS is caused by persistent infection, but this is not believed to be true because of the inability to detect infectious organisms after standard treatment. A vaccine for Lyme disease was marketed in the United States between 1998 and 2002, but was withdrawn from the market due to poor sales. Research is ongoing to develop new vaccines.