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Onchocerciasis DEC Contraindicated — SCE Infectious Diseases MCQ

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ModerateTropical & Imported InfectionsOnchocerciasis DEC ContraindicatedSCE Infectious Diseases

A 30-year-old man from West Africa presents with a painless subcutaneous nodule on his right thigh. He reports being bitten by blackflies near a river. On slit-lamp examination, microfilariae are visible in the anterior chamber of his left eye. What is the appropriate treatment?

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Correct answer: A — Ivermectin 150 µg/kg as a single dose — repeated every 6–12 months (microfilaricidal); Doxycycline 100 mg BD for 4–6 weeks (macrofilaricidal anti-Wolbachia strategy) for definitive cure

Onchocerciasis with ocular involvement (microfilariae in the anterior chamber — a sight-threatening finding). Ivermectin 150 µg/kg single dose kills microfilariae and is repeated 6–12 monthly. CRITICALLY: DEC is CONTRAINDICATED in Onchocerciasis — it causes a severe Mazzotti reaction (acute inflammatory response from rapid microfilarial killing) that can worsen ocular disease and cause blindness. Doxycycline (anti-Wolbachia) provides macrofilaricidal activity (kills adult worms over 4–6 weeks) and is the closest approach to cure.

Reference: WHO 2022 – Onchocerciasis; UKHSA 2023 – Filariasis