Dracunculus medinensis, commonly known as the guinea worm, is an example of a multicellular parasitic helminth. Infection usually occurs when an individual consumes drinking water that contains water fleas infected with guinea-worm larvae. As the adult worm gradually works its way out of the host's skin, it causes debilitating symptoms such as dizziness, vomiting, diarrhea, and painful ulcers on the legs and feet. Thanks to coordinated global sanitation efforts to improve drinking water, cases of guinea-worm disease have plummeted from an estimated ${}3.5$ million in the mid-${}1980$s to only ${}126$ reported cases in ${}2014$.