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Loiasis — SCE Infectious Diseases MCQ

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HardTropical & Imported InfectionsLoiasisSCE Infectious Diseases

A 35-year-old man from Nigeria presents with a painless, progressively enlarging nodule on his forearm. He reports intermittent episodes of localised swelling that migrate along the forearm (Calabar swellings). Blood film taken at midday shows a sheathed microfilaria. Eosinophil count is 4.2 × 10⁹/L. What is the most likely diagnosis?

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Correct answer: E — Loiasis (Loa loa)

Calabar swellings (migratory subcutaneous angioedema), sheathed microfilariae in daytime blood (diurnal periodicity), eosinophilia, and West/Central African origin are diagnostic of Loiasis (Loa loa). The adult worm may migrate across the subconjunctival space (eye worm). Treatment is Diethylcarbamazine (DEC), but caution is needed — high microfilarial loads (>8,000/mL) risk encephalopathy with DEC, and Albendazole may be used first to reduce microfilarial counts. Ivermectin is relatively contraindicated due to risk of encephalopathy in high-load Loa loa.

Reference: WHO 2022 – Filariasis guidelines; UKHSA 2023 – Imported filariasis