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

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

Answer: (B)

Epidemic relapsing fever is transmitted by the body louse, Pediculus humanus corporis. The Borrelia recurrentis spirochetes live in the lice, and transmission to a new person occurs when the louse feeds or contaminates the bite with its feces, which the person then inoculates by scratching or by contact with mucous membranes. This makes body lice the classic vector for this form of relapsing fever. The other options are vectors for different diseases: fleas transmit plague, mosquitoes transmit diseases like malaria and dengue, and ticks transmit various infections (including tick-borne relapsing fever caused by different Borrelia species in some settings).