The bacteria that cause Lyme disease in the United States, Borrelia burgdorferi, are spread to people through the bites of infected ticks. The blacklegged tick (or deer tick, lxodes scapularis) transmits infection in the northeastern, mid-Atlantic, and north-central United States. The western blacklegged tick (lxodes pacificus) transmits infection in areas along the Pacific Coast. The percentage of ticks that are infected ranges from none to over 50%, depending on the area and life stage. Blacklegged ticks found in most areas of the southeastern United States are almost never infected.

Source: CDC