Lyme borreliosis (or Lyme disease) is an infectious disease caused by the bacterium Borrelia burgdorferi. Lyme disease was named after a cluster of cases that occurred in Old Lyme, Connecticut in the United States, in 1974. The disease may have various symptoms, the most common being a rash called erythema migrans.
Human beings become infected after being bitten by hard-bodied ticks ( Ixodes species ) that are infected with B. burgdorferi. Ticks become infected when they feed on birds or mammals that carry the bacterium in their blood.