Lyme disease is caused by infection with the bacterium Borrelia burgdorferi. Lyme disease is transmitted by the bite of an infected black-legged tick (Ixodes scapularis). According to the Centers for Disease Control and Prevention (CDC), the tick must be attached to the skin for 36 to 48 hours or more for bacterium transmission to occur. Typical symptoms include fever, headache, fatigue, and a characteristic skin rash called erythema migrans. If left untreated, infection can spread to joints, the heart, and the nervous system. Lyme disease is diagnosed based on symptoms, physical findings (e.g., rash), and the possibility of exposure to infected ticks; laboratory testing is helpful if used correctly and performed with validated methods. Most cases of Lyme disease can be treated successfully with a few weeks of antibiotics. Steps to prevent Lyme disease include using insect repellent, removing ticks promptly, applying pesticides, and reducing tick habitat. The ticks that transmit Lyme disease can occasionally transmit other tickborne diseases as well. Lyme disease is the most commonly reported vectorborne illness in the United States.