A 30-year-old man from a tribal district of Odisha presents with pruritic papular rash over the buttocks, subcutaneous palpable nodules, and visual field defects. Skin biopsy of a nodule shows coiled adult worms. Which method provides definitive laboratory confirmation of active infection?

• A Serological detection of circulating filarial antigen (Og4C3)
• B Detection of microfilariae in a midnight peripheral blood smear
• C Isolation of the parasite from aqueous humour by anterior chamber tap
• D Demonstration of microfilariae in superficial skin snips taken from the iliac crest region ✓

Explanation

Onchocerca volvulus microfilariae reside in the dermis, not the blood, so the diagnostic standard is examination of superficial skin snips, classically from the iliac crest in Africa, for motile microfilariae. Nodules (onchocercomata) contain adult worms, and ocular involvement causes river blindness. Blood smears detect lymphatic filarial parasites such as Wuchereria bancrofti, whose microfilariae are nocturnally periodic in blood. Circulating filarial antigen tests target Wuchereria, not Onchocerca.

Reference: Paniker's Textbook of Medical Parasitology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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