Trichuriasis — DTM&H MCQ

Correct answer: B — Trichuris trichiura

The correct answer is B, Trichuris trichiura. The description of adult worms shaped like a whip, with a thin, thread-like anterior end embedded in the mucosa and a thicker posterior end, is pathognomonic for the whipworm, and the barrel-shaped eggs with clear bipolar (polar) plugs seen on stool microscopy confirm this. Trichuris trichiura lives in the caecum and ascending colon, and heavy worm burdens can extend into the appendiceal lumen, producing luminal obstruction and secondary appendicitis, exactly as described in this Nigerian patient (endemic soil-transmitted helminth exposure). Diagnosis is by stool ova and parasite microscopy, and treatment is with a benzimidazole such as mebendazole or albendazole, although single-dose cure rates for Trichuris are known to be lower than for other soil-transmitted helminths. Why the other options are wrong: C. Ascaris lumbricoides: this is a large, round, unsegmented roundworm (not whip-shaped) that produces mammillated (rough-coated), oval eggs without bipolar plugs; it more typically causes intestinal or biliary obstruction, not the whip morphology described. E. Ancylostoma duodenale: hookworms are small, curved worms with a buccal capsule bearing teeth, and their eggs are thin-shelled and oval with no bipolar plugs; they cause anaemia via blood-sucking, not appendicitis with whip-shaped worms. A. Enterobius vermicularis: pinworms are small, white, thread-like worms found perianally, and their eggs are asymmetrically flattened on one side, not barrel-shaped with plugs. D. Strongyloides stercoralis: this nematode is diagnosed by finding rhabditiform larvae in stool, not eggs, and adults are not whip-shaped. Key point: whip-shaped adult worms plus barrel-shaped, bipolar-plugged eggs equal Trichuris trichiura, a recognised though uncommon cause of appendicitis in endemic regions.

Reference: BNF (NICE), Mebendazole: indications and treatment of threadworm and other intestinal nematode infections including trichuriasis, bnf.nice.org.uk