The causative agent, Borrelia burgdorferi , is a type of spirochete.
Spirochetes are long, thin, spiral-shaped bacteria.
Other spirochetes include the causative agents of syphilis, relapsing fever, and gum disease. The bacterium is thousands of times larger than a virus. However, it still requires a powerful microscope to see one. Roughly 1,500 Bb must be laid end to end to equal one inch. About 100,000 of Bb laid side to side would equal one inch.