Onchocerciasis — DTM&H MCQ
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Correct answer: E — Ivermectin after Loa loa risk assessment
The correct answer is E, ivermectin after Loa loa risk assessment. The clinical picture (chronic pruritus, depigmented shin lesions, "leopard skin", visual impairment, and unsheathed microfilariae on skin snips) is classic for onchocerciasis (Onchocerca volvulus), which is definitively diagnosed by skin snip microscopy showing unsheathed microfilariae, distinguishing it from lymphatic filariasis where microfilariae are sheathed and found in blood. Ivermectin is the drug of choice, killing microfilariae and reducing transmission and ocular/dermal disease progression. Because northern Ghana lies within the Loa loa co-endemic belt of West/Central Africa, and high Loa loa microfilarial loads predispose to severe post-ivermectin neurological adverse events including encephalopathy, current product guidance mandates assessment of Loa loa risk (history of eye worm, blood microfilarial counts) before treating with ivermectin. This risk-stratified approach is the standard of care and the discriminating feature the question is testing. Why the other options are wrong: C. Praziquantel: This is the treatment for schistosomiasis and other trematode/cestode infections; it has no activity against filarial nematodes such as O. volvulus. A. Metronidazole: This is an antiprotozoal and antibacterial agent (used for amoebiasis, giardiasis, anaerobic infections) with no efficacy against microfilariae. D. Fluconazole: This is an antifungal agent, entirely irrelevant to a helminth infection presenting with skin snip positive microfilariae. B. Chloroquine: This is used for malaria (and some autoimmune conditions), not for filarial disease, and has no microfilaricidal action against O. volvulus. Key point: Unsheathed microfilariae on skin snip confirm onchocerciasis, but before giving ivermectin in Loa loa co-endemic West Africa, always screen for heavy Loa loa microfilaraemia to avoid encephalopathy.
Reference: Ivermectin 3 mg Tablet, Summary of Product Characteristics, electronic medicines compendium (emc), medicines.org.uk, https://www.medicines.org.uk/emc/product/101483/smpc