Which spirochete is known for causing epidemic relapsing fever?

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

Answer: (B)

Relapsing fever from spirochetes happens because the bacteria can vary their surface antigens, causing the fever to recur as the immune system reorients to each new variant. The epidemic form is classically caused by Borrelia recurrentis, which is transmitted by body lice and seen in crowded, unsanitary conditions. This association with outbreaks and lice transmission makes it the best answer for epidemic relapsing fever. In contrast, Borrelia burgdorferi causes Lyme disease transmitted by ticks, Treponema pallidum causes syphilis, and Leptospira causes leptospirosis from animal urine exposure—diseases with distinct presentations and vectors, not the epidemic relapsing fever pattern.