A 40-year-old man living in a slum with heavy louse infestation presents with his third febrile episode in 3 weeks, each lasting 3 to 5 days with intervening afebrile periods. During a febrile spike, a Giemsa-stained peripheral blood smear shows loosely coiled spirochaetes in the plasma between red cells. What is the causative organism and its mode of transmission?

• A Leptospira interrogans, contact with contaminated water
• B Treponema pallidum, sexual contact
• C Borrelia burgdorferi, Ixodes tick
• D Borrelia recurrentis, human body louse ✓

Explanation

Louse-borne relapsing fever is caused by Borrelia recurrentis and is transmitted by the human body louse Pediculus humanus corporis. Unlike other borreliae, D. recurrentis has no animal reservoir and humans are the sole host. Spirochaetaemia is highest during the febrile phase, making Giemsa or dark-field examination of peripheral blood during fever the diagnostic method of choice. Antigenic variation of outer surface proteins explains the recurrent episodes, a mechanism already tested elsewhere, so this item focuses on diagnosis and vector.

Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.