The Worm That Blinds

Onchocerca volvulus, spread by riverside blackflies, causes river blindness. An adult worm releases millions of tiny larvae called microfilariae that wander through the skin and eyes.

The twist: the worms barely harm you while alive. The damage comes when they die. Your immune system attacks the decaying larvae so fiercely that, over years, it destroys your own vision.

WHO estimates roughly 25 million people are infected and about 300,000 are blind. In parts of West Africa, whole villages once abandoned fertile riverbanks because living near the water meant going blind.