A parasitic worm called
Onchocerca volvulus affects 25 million people around the world in one of the most revolting ways possible. The larvae of this tiny worm, found in sub-Saharan Africa and Latin America, can live for more than 10 years in a person’s skin, and that’s not even the worst part - they often make their way into their eyes.
Source: http://www.sciencealert.com/features/20142008-26044-2.html
