Strongyloidiasis — DTM&H MCQ

Correct answer: E — Ivermectin 200 µg/kg daily for 2 days

The correct answer is E, ivermectin 200 microgram/kg daily for 2 days. This clinical picture (recurrent urticaria, cough, epigastric pain, with rhabditiform larvae seen in stool and duodenal aspirate) is classic for Strongyloides stercoralis infection, and ivermectin is the treatment of choice because it achieves cure rates well above 90 percent by paralysing and killing the adult worms in the intestinal mucosa, interrupting the unique autoinfective cycle that allows Strongyloides to persist for decades. The autoinfective larval migration also explains the pulmonary (cough, urticaria from larva currens/Loeffler-like picture) and gastrointestinal features seen together in this patient. Two consecutive daily doses are used rather than a single dose in symptomatic or higher burden infection to ensure larvae emerging during the autoinfective cycle are also cleared. Why the other options are wrong: C. Albendazole 400 mg daily for 3 days: albendazole is active against many soil-transmitted helminths but has markedly lower efficacy against Strongyloides, with cure rates around 40 to 70 percent, so it is reserved for when ivermectin is unavailable or contraindicated. A. Mebendazole 100 mg twice daily for 3 days: mebendazole has poor and unreliable activity against Strongyloides stercoralis and is not recommended for this infection. D. Praziquantel 20 mg/kg three times daily: praziquantel is a trematode/cestode agent (schistosomiasis, tapeworms) and has no activity against nematodes such as Strongyloides. B. Thiabendazole 25 mg/kg twice daily for 3 days: although historically used for strongyloidiasis, thiabendazole is poorly tolerated (frequent nausea, dizziness, hepatotoxicity) and has been superseded by ivermectin, which is better tolerated and more effective; it is no longer available in the UK. Key point: Rhabditiform larvae in stool or duodenal aspirate with urticaria, cough and abdominal symptoms indicates Strongyloides stercoralis, for which ivermectin (200 microgram/kg daily for 1 to 2 days) is first-line therapy due to superior efficacy over benzimidazoles.

Reference: Ivermectin (Stromectol) Summary of Product Characteristics, electronic medicines compendium (emc), Strongyloidiasis dosing section, https://www.medicines.org.uk/emc/product/ivermectin