Yaws — DTM&H MCQ

Correct answer: B — Yaws

The correct answer is B, Yaws. Yaws is caused by Treponema pallidum subspecies pertenue and is a non-venereal endemic treponematosis transmitted by direct skin contact, classically affecting children in warm, humid, tropical communities. The primary lesion is a papilloma or papillomatous ulcer on an exposed site such as the leg, sometimes called the mother yaw, which heals but is followed weeks to months later by secondary lesions and painful periostitis (dactylitis or long bone swelling) as the organism disseminates haematogenously. Because T. pertenue is a treponeme, patients test positive on both non-treponemal (RPR/VDRL) and treponemal (TPPA/TPHA) serology, exactly as described in the stem, and this serological pattern combined with the papillomatous skin lesion and periosteal reaction is the classic diagnostic triad. WHO recognises this presentation as diagnostic of yaws in endemic settings and mass treatment programmes use single dose oral azithromycin as first line therapy. Why the other options are wrong: D. Buruli ulcer: caused by Mycobacterium ulcerans, presents as a painless nodule that progresses to a large undermined necrotic ulcer, not a papilloma, and does not cause periostitis or give positive treponemal serology. E. Leprosy: caused by Mycobacterium leprae, presents with hypopigmented or erythematous anaesthetic skin patches and peripheral nerve thickening, not papillomatous ulcers or acute painful periostitis, and treponemal serology is negative. A. Cutaneous leishmaniasis: presents as a chronic painless ulcer with a raised indurated edge at a sandfly bite site, has no bone involvement and is diagnosed by parasitological or PCR demonstration of Leishmania, not treponemal serology. C. Scabies: causes intensely itchy burrows and papules from Sarcoptes scabiei infestation, has no systemic bone involvement and no serological treponemal association. Key point: Papillomatous skin lesions plus painful periostitis in a child from an endemic tropical area with positive treponemal serology is the classic triad of yaws.

Reference: World Health Organization, Yaws fact sheet and diagnostic/treatment guidance (WHO, updated 2023), https://www.who.int/news-room/fact-sheets/detail/yaws; corroborated by Merck Manual Professional Edition, Bejel, Pinta, and Yaws section