Lyme disease is a bacterial infection caused by the bacterium Borrelia burgdorferi and, rarely, Borrelia mayonii. It is transmitted to humans through the bite of infected blacklegged ticks. The symptoms of Lyme disease can vary depending on the stage of infection and may 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. It is important to seek medical attention if you observe any symptoms of Lyme disease and have had a tick bite, live in an area known for Lyme disease, or have recently traveled to an area where Lyme disease occurs.