Lyme disease is a bacterial infection caused primarily by the Borrelia burgdorferi bacteria, which is transmitted to humans through the bite of infected blacklegged ticks (also called deer ticks). The disease is most common in forested or grassy areas where these ticks live, particularly in certain parts of the United States (Northeast, mid-Atlantic, upper Midwest), Europe, and Canada.

The early signs of Lyme disease often include a characteristic expanding red rash called erythema migrans at the site of the tick bite, fever, headache, fatigue, and sometimes joint pain. If untreated, the infection can spread to the joints, heart, and nervous system, causing symptoms like joint swelling, facial paralysis, severe headaches, and heart palpitations. Diagnosis is based on symptoms, history of tick exposure, and sometimes laboratory tests.

Lyme disease is treatable with antibiotics, usually over a few weeks, which can successfully clear the infection if given early. Preventing tick bites by wearing protective clothing and using insect repellents is key to reducing risk. In rare cases, symptoms may persist after treatment, a condition known as Post-Treatment Lyme Disease Syndrome (PTLDS).

In summary, Lyme disease is a tick-borne bacterial infection causing varied symptoms from rash and flu-like illness to serious complications if untreated, with effective antibiotic treatment available to most patients.