Which organism is the etiologic agent of Lyme disease?

• A. Leptospira interrogans
• B. Borrelia recurrentis
• C. Borrelia burgdorferi
• D. Treponema pallidum pallidum

Answer: (C)

Lyme disease is caused by a spirochete transmitted by Ixodes ticks. The organism Borrelia burgdorferi is the primary etiologic agent in North America, a slender corkscrew-shaped, gram-negative bacterium. In clinical practice, Lyme disease often begins with an expanding erythema migrans rash and may progress to migratory arthritis, carditis, or neurologic symptoms if not treated. Laboratory detection typically relies on a two-step serologic test or, in certain cases, molecular methods. The other organisms listed are responsible for different diseases with distinct vectors and clinical pictures: Leptospira interrogans causes leptospirosis, Borrelia recurrentis causes relapsing fever, and Treponema pallidum pallidum causes syphilis.