Enterobiasis — DTM&H MCQ

Correct answer: B — Albendazole 400 mg single dose repeated after 2 weeks

A) Albendazole 400 mg single dose repeated after 2 weeks is correct. The presentation (nocturnal perianal pruritus, visible white thread-like worms, and plano-convex eggs on sellotape test) is classic for Enterobius vermicularis (threadworm). Albendazole is a benzimidazole that inhibits helminth microtubule formation and glucose uptake, killing adult worms, but it has no ovicidal effect; a repeat dose at two weeks clears worms that hatch from residual eggs, which is why the two-dose regimen is recommended rather than a single dose alone. This benzimidazole approach is standard in resource-limited and tropical settings such as rural Cameroon, where albendazole is widely available through mass deworming programmes and is the WHO-recommended agent for soil-transmitted helminths including Enterobius. Why the other options are wrong: B) Praziquantel 40 mg/kg single dose: used for schistosomiasis and cestode infections, acting on trematode/cestode tegument calcium channels; no activity against nematodes such as Enterobius. C) Ivermectin 200 microgram/kg single dose: first-line for strongyloidiasis and onchocerciasis but not the recommended agent for enterobiasis, which responds poorly and inconsistently compared with benzimidazoles. D) Metronidazole 400 mg three times daily for 5 days: an antiprotozoal/antianaerobic agent (giardiasis, amoebiasis, anaerobic infections) with no anthelmintic activity against pinworm. E) Niclosamide 2 g single dose: targets cestodes (Taenia, Hymenolepis) by inhibiting tapeworm mitochondrial oxidative phosphorylation; ineffective against nematode infections like threadworm. Key point: nocturnal perianal itch plus plano-convex eggs on sellotape test confirms Enterobius vermicularis, treated with a benzimidazole (albendazole) given as two doses two weeks apart to eliminate both adult worms and newly hatched larvae from residual eggs.

Reference: NICE CKS, Threadworm: Scenario Management, 2023 (https://cks.nice.org.uk/topics/threadworm/); BNF, Albendazole, Enterobiasis dosing (https://bnf.nice.org.uk/drugs/albendazole/)