A medical officer posted to a riverine district in West Africa encounters patients with palpable nodules containing coiled worms and punctate keratitis. The vector of this infection is a day-biting fly whose immature stages develop attached to vegetation in:

• A Fast-flowing, highly oxygenated streams and rivers ✓
• B Stagnant ponds rich in organic matter
• C Water-holding containers in domestic compounds
• D Flooded rice paddies during the monsoon

Explanation

Onchocerciasis (river blindness) is transmitted by the blackfly Simulium damnosum, whose larvae and pupae attach to rocks and submerged vegetation in fast-flowing, well-oxygenated rapids, which is why the disease clusters near rivers. Stagnant organically polluted water supports Culex quinquefasciatus, domestic containers support Aedes aegypti, and rice paddies support Culex tritaeniorhynchus. The breeding-site preference dictates control strategies such as larviciding rivers, since the blackfly cannot be easily controlled at household level.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.