The guinea worm is a nasty, painful parasite that is caused when people drink water contaminated with roundworm larvae. Now after a 30-year campaign to eradicate guinea worm only 126 cases were reported in 2014—down from 3.5 million in 1986. Guinea worm is on its way to being the second eradicated parasitic disease following small pox. A world free of guinea worm is foreseeable because it’s only transmitted through contaminated water—give everyone access to clean water and the guinea worm is toast.