What is the vector for Onchocerca volvulus and what is the hallmark clinical feature?

• A. Mosquito; fever and chills
• B. Tse-tse fly; sleeping sickness
• C. Blackfly; river blindness with pruritus and skin nodules
• D. Sandfly; mucocutaneous lesions

Answer: (C)

The key idea is that Onchocerca volvulus is transmitted by a blackfly that breeds in fast-flowing rivers. When the fly bites, it injects larvae that mature in the skin and form subcutaneous nodules. The adult female releases microfilariae that migrate through the skin and into the eyes, causing intense itching and dermatitis and, over time, ocular damage that can lead to river blindness. So the vector is the blackfly, and the hallmark clinical feature is river blindness accompanied by pruritus and skin nodules. Other listed vectors are associated with different diseases (mosquitoes with malaria, tse-tse flies with African sleeping sickness, sandflies with leishmaniasis).