Lyme disease is caused by which organism?

• A. Borrelia burgdorferi
• B. Rickettsia rickettsii
• C. Ehrlichia chaffeensis
• D. Bartonella henselae

Answer: (A)

Lyme disease is caused by Borrelia burgdorferi, a spirochete transmitted by Ixodes ticks. This organism is the classic agent associated with Lyme disease, producing features such as erythema migrans early on and potential later manifestations like migratory arthritis, carditis, or neuropathy if not treated. It differs from the other organisms listed, which cause different illnesses: Rickettsia rickettsii leads to Rocky Mountain spotted fever with a petechial rash and vasculitis; Ehrlichia chaffeensis causes ehrlichiosis with fever and cytopenias; Bartonella henselae causes cat-scratch disease with regional lymphadenopathy. The specific pathogen name identifies the Lyme disease etiology, making it the best answer.