Lyme disease is a bacterial infection caused by Borrelia bacteria, commonly Borrelia burgdorferi, which is transmitted to humans through the bite of infected blacklegged ticks (also known as deer ticks). These ticks are commonly found in wooded and grassy areas, especially in the northeastern, mid-Atlantic, and upper Midwestern United States, as well as in parts of Europe and Canada. The disease often starts with early symptoms such as a characteristic expanding red rash called erythema migrans at the site of the tick bite, fever, headache, fatigue, and sometimes flu-like symptoms. The rash is usually not itchy or painful and appears about a week after the tick bite. About 70-80% of people infected develop this rash. If Lyme disease is not treated promptly, the infection can spread to joints, the heart, and the nervous system, causing more serious complications such as joint pain and swelling, facial paralysis, severe headaches, neck stiffness, and heart palpitations. Lyme disease may progress through stages, with symptoms varying based on the stage of the infection. Lyme disease is diagnosed based on symptoms, history of tick exposure, and sometimes blood tests for specific antibodies. Effective treatment typically involves antibiotics such as doxycycline or amoxicillin for a few weeks, and early treatment usually leads to a quick recovery. Preventive measures include avoiding tick bites by wearing protective clothing, using insect repellents, and checking for ticks after spending time outdoors. Lyme disease is the most common tick-borne disease in the Northern Hemisphere and is most frequently reported in the warmer months when ticks are active and people spend more time outdoors. Transmission requires the tick to be attached for more than 24 hours in most cases. In summary, Lyme disease is a bacterial infection spread by tick bites that can cause various symptoms initially as a rash and flu-like illness, with potential serious complications if untreated, but it is usually treatable with early antibiotics. This information is supported by authoritative health sources including the CDC, Mayo Clinic, and MedlinePlus.