Borrelia burgdorferi is the etiologic agent of which disease?

• A. Lyme disease
• B. Rat-bite fever
• C. Relapsing fever
• D. Q fever

Answer: (A)

This question centers on which disease Borrelia burgdorferi causes. Borrelia burgdorferi is a spirochete transmitted by Ixodes ticks (the deer tick). It causes Lyme disease, which often begins with an expanding erythema migrans rash and can progress to involve the nervous system, heart, and joints if not treated, leading to neurologic symptoms, carditis, and migratory arthritis. This distinguishes it from other infections listed: rat-bite fever is caused by Streptobacillus moniliformis (or Spirillum minus in some regions); relapsing fever is caused by Borrelia recurrentis or related species; Q fever is caused by Coxiella burnetii. So the pathogen Borrelia burgdorferi is the cause of Lyme disease.