Guinea worm disease, also known as dracunculiasis, is close to being success story No. 2. As of 2009, the world was about 3,000 cases away from eradication -- a far cry from 1986 when 3.5 million people were infected [source: The Carter Center]. People contract the illness by drinking stagnant water containing a tiny water flea infected with the larvae of the Guinea worm. These larvae mate inside a person's stomach and produce female worms that can grow upwards of 3-feet (.91 meters) long. The worm then causes swelling and painful blisters as it wiggles its way out through the person's skin -- typically on the feet and ankles. To relieve the pain and burning from the blisters, people soak in a nearby water source, causing the worm to release its larvae. Water fleas then swallow the larvae, beginning the process all over again.