Louse-borne relapsing fever — DTM&H MCQ

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ModerateTropical Bacterial InfectionsLouse-borne relapsing feverDTM&H

A 22-year-old Eritrean refugee presents with multiple episodes of high fever lasting 3-5 days separated by afebrile periods of 5-7 days. He has been living in crowded conditions with poor hygiene. Blood film during a febrile episode shows spirochaetes. What is the vector?

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Correct answer: A — Pediculus humanus corporis (body louse)

The correct answer is A, Pediculus humanus corporis (body louse). The stem describes classic louse-borne relapsing fever (LBRF): a refugee from an endemic region (Eritrea/Horn of Africa), living in crowded, unhygienic conditions that favour louse infestation, with recurrent high fevers separated by symptom-free intervals and spirochaetes visible on a blood film taken during the febrile episode. LBRF is caused by Borrelia recurrentis, which is transmitted exclusively by the human body louse; humans are infected when a crushed, infected louse contaminates broken skin or mucosae, not by louse bite alone. The louse vector explains the epidemic potential of this disease in displaced populations, refugee camps and conflict settings where clothing is worn continuously and washing facilities are scarce. Why the other options are wrong: C. Ornithodoros soft tick: This is the vector for tick-borne relapsing fever (multiple Borrelia species), which is typically sporadic/zoonotic rather than epidemic, and is not linked to crowding or poor hygiene in the way described. E. Ixodes hard tick: Ixodes species transmit Lyme borreliosis and other tick-borne infections, not relapsing fever; they are not associated with body infestation from poor hygiene. B. Cimex lectularius (bed bug): Bed bugs are not established biological vectors for Borrelia species and play no role in relapsing fever transmission. D. Pulex irritans (human flea): Fleas transmit organisms such as Yersinia pestis and Rickettsia typhi, not Borrelia recurrentis; there is no recognised flea-borne relapsing fever. Key point: Recurrent fevers with spirochaetaemia in a refugee from crowded, unhygienic conditions points to louse-borne relapsing fever, transmitted by Pediculus humanus corporis via contamination rather than bite.

Reference: Warrell DA. Louse-borne relapsing fever (Borrelia recurrentis infection). Epidemiology and Infection. 2019;147:e106. Oxford/UK authored review, doi:10.1017/S0950268819000116