Louse-borne relapsing fever — DTM&H MCQ

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HardTropical bacterial infectionsLouse-borne relapsing feverDTM&H

A 31-year-old man living in an overcrowded refugee camp has recurrent episodes of high fever separated by afebrile periods. During fever, a blood film shows spirochaetes and he has body lice in his clothing seams. What is the most likely diagnosis?

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Correct answer: C — Louse-borne relapsing fever

The correct answer is C, louse-borne relapsing fever. This is caused by Borrelia recurrentis, transmitted by the human body louse Pediculus humanus corporis, and classically produces cyclical high fevers with afebrile intervals as antigenic variation allows the organism to evade clearing antibody responses. The combination of overcrowding, body lice in clothing seams, and spirochaetes seen on a Giemsa-stained blood film taken during a febrile episode is the textbook diagnostic triad for this condition, which occurs in outbreaks among displaced and refugee populations living in poor hygiene conditions. Microscopic detection of spirochaetes in blood during fever confirms the diagnosis, and clinicians treating it must anticipate a Jarisch-Herxheimer reaction after starting antibiotics. Why the other options are wrong: A. Malaria due to P. vivax: Vivax malaria causes tertian fever cycles but the blood film shows intraerythrocytic Plasmodium parasites, not spirochaetes, and lice are not a vector. D. Leptospirosis: Leptospira are spirochaetes but transmission is via contaminated water or animal urine, not body lice, and organisms are rarely visualised on a standard peripheral blood film due to their thinness. B. Brucellosis: Brucella causes undulant fever but is acquired from unpasteurised dairy or infected animals, is a small intracellular coccobacillus, and does not appear as spirochaetes on blood film. E. Epidemic typhus: Also transmitted by body lice and occurs in identical overcrowded settings, but is caused by Rickettsia prowazekii, an obligate intracellular organism that is never seen as free spirochaetes on a blood film. Key point: Body lice plus relapsing fever plus visible spirochaetes on a febrile blood film points specifically to Borrelia recurrentis, distinguishing it from the lice-borne but rickettsial epidemic typhus.

Reference: European Centre for Disease Prevention and Control, Rapid Risk Assessment: Louse-borne relapsing fever in the EU/EEA (2015), https://www.ecdc.europa.eu/sites/default/files/media/en/publications/Publications/louse-borne-relapsing-fever-in-eu-rapid-risk-assessment-17-nov-15.pdf