Borrelia burgdorferi transmitted by the bite of a deer tick . Most cases occur in the Northeast, upper Midwest, and the Pacific Coast. Mice and deer are the most commonly infected animals that serve as hosts to the tick .
Most infections occur in the summer.
The disease is difficult to diagnose because the symptoms mimic other diseases. The second stage develops weeks to months after the skin lesions disappear. It is characterized by neurological or cardiac symptoms. The third stage develops later on and is characterized by arthritis. Risk factors include recent tick bite or recent outdoor activities in endemic areas.