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 host to the tick. Most infections occur in the summer. The disease is difficult to diagnose, because the symptoms mimic other diseases. A few months after the bite, muscle paralysis, joint inflammation, neurological symptoms and sometimes heart symptoms may occur. The initial infection is called primary Lyme disease.