The etiologic agent of epidemic relapsing fever is Borrelia recurrentis and is commonly transmitted by which vector?

• A. Fleas
• B. Mosquitoes
• C. Ticks
• D. Lice

Answer: (D)

Epidemic relapsing fever is transmitted by the human body louse. The Borrelia recurrentis spirochete is carried by infected body lice, and transmission occurs when the lice bite a person and defecate. The infected louse feces can enter the bite wound or mucous membranes as the person scratches, allowing spirochetes to invade the bloodstream. This louse-borne route is why outbreaks occur in crowded or unsanitary conditions where body lice spread readily. Other vectors listed align with different diseases—flea transmission is classic for plague, mosquitoes for diseases like malaria and dengue, and ticks for tick-borne relapsing fever caused by other Borrelia species—so the correct vector for epidemic relapsing fever specifically is the body louse.