Tungiasis — DTM&H MCQ

Correct answer: A — Tungiasis

Tungiasis (A) is correct: painful periungual/toe papules with a central black dot in a barefoot child from rural Brazil are classic for infestation by the female sand flea Tunga penetrans, which burrows head-first into the epidermis, leaving its rear end (with the black dot representing the exposed anus/breathing opening) exposed at the skin surface. The flea is embedded within the lesion itself rather than merely leaving eggs or larvae, which is the key distinguishing clinical sign here. Endemic areas include sandy soil in rural Latin America and sub-Saharan Africa, and lack of footwear is the principal risk factor, exactly as described in the stem. Why the other options are wrong: D. Cutaneous larva migrans: caused by hookworm larvae penetrating skin, producing a serpiginous, migrating, itchy track rather than a fixed papule with an embedded organism and black dot. E. Scabies: caused by Sarcoptes scabiei mites producing widespread intensely itchy burrows, typically in finger webs, wrists and flexures, not painful solitary toe papules containing a visible insect. C. Myiasis: caused by fly larvae (maggots) infesting tissue, usually presenting as a boil-like lesion with a central punctum through which the larva breathes and periodically moves, but the causative organism is a larva, not an adult insect embedded whole. B. Yaws: a treponemal infection causing papillomatous skin lesions and later bone involvement, with no insect vector or black-dot sign, and no association with barefoot walking on sandy soil. Key point: a painful toe papule with a central black dot and a palpable embedded insect in a barefoot patient from an endemic tropical region is pathognomonic for tungiasis due to the burrowed female Tunga penetrans flea.

Reference: Clinical parasitology overview of Tunga penetrans (tungiasis): characteristic papular or nodular lesion with a central black dot representing the flea's exposed posterior end, ScienceDirect Topics, https://www.sciencedirect.com/topics/medicine-and-dentistry/tungiasis