Known commonly as the "Guinea worm," this is one of the oldest documented human parasites, with tales of its behavior reaching as far back as the 2nd century BC in accounts penned by Greek chroniclers. It affects humans, dogs, cats, horses, cattle, and other animals, especially in Africa and Asia.

The parasite enters a host after the ingestion of water contaminated with copepods (water fleas) infested with guinea worm larvae. About a year later, the worm creates a blister in the human host's skin, usually on the leg or foot. Within 72 hours, the blister ruptures, exposing one end of the emerging worm. This blister causes a very painful burning sensation as the worm emerges. Infected people often immerse the affected limb in water to relieve the burning sensation, thus allowing the adult female to release hundreds of thousands of guinea worm larvae, contaminating the water supply once again.