Onchocerciasis — DTM&H MCQ

Correct answer: B — Ivermectin 150 µg/kg repeated every 6-12 months

The correct answer is B, ivermectin 150 microgram/kg repeated every 6 to 12 months. This patient has classic onchocerciasis (river blindness), confirmed by unsheathed microfilariae on skin snips and microfilariae visualised in the anterior chamber on slit-lamp examination. Ivermectin is microfilaricidal, rapidly clearing microfilariae from skin and eye with a comparatively mild post-treatment reaction, and because it does not kill adult worms, repeat dosing every 6 to 12 months is required until the adult worms die off or as long as transmission risk persists. This regimen underpins both individual case management and the WHO/UK-endorsed mass drug administration programmes for onchocerciasis control. Why the other options are wrong: D. DEC 6 mg/kg daily for 12 days: diethylcarbamazine is contraindicated in onchocerciasis because rapid microfilarial killing provokes an intense Mazzotti reaction and can precipitate severe, sight-threatening intraocular inflammation. A. Doxycycline 200 mg daily for 4-6 weeks: this targets the Wolbachia endosymbiont and has useful macrofilaricidal/sterilising adjunct effects, but it is slow-acting and not the primary treatment for acute microfilarial disease with ocular involvement. C. Albendazole 400 mg twice daily for 21 days: albendazole has limited efficacy against Onchocerca volvulus and is not recommended as first-line therapy for this infection. E. Suramin intravenously: suramin is an older macrofilaricidal agent with significant toxicity (including renal and marrow toxicity) and has been abandoned in favour of safer regimens. Key point: In onchocerciasis, ivermectin (not DEC, which risks a severe Mazzotti reaction and ocular damage) is the treatment of choice, given repeatedly every 6 to 12 months because it does not kill adult worms.

Reference: British Infection Association, UK guidelines for the investigation and management of eosinophilia in returning travellers and migrants, Journal of Infection, 2024 (section on onchocerciasis management: ivermectin as first-line treatment, DEC contraindicated). https://www.journalofinfection.com/article/S0163-4453(24)00262-7/fulltext