The worm that causes river blindness appears to be developing resistance to the sole drug that's effective against it, a study in West Africa shows. The finding is bad news in the fight against this parasite, Onchocerca volvulus, which infects roughly 37 million people worldwide.
The river blindness parasite spreads among people bitten by certain black flies that live near fast-flowing water. The worms can survive inside a person for 15 years. The female worms produce larvae that cause itchy skin and scarring of the cornea, which leads to blindness.
Since 1987, widespread use of the drug ivermectin has stalled river blindness in many countries. The once-a-year tablet doesn't kill adult worms living in a human host, but it wipes out larvae and hampers the females' ability to reproduce.