Dracunculiasis, also called Guinea-worm disease, is a parasitic infection by the Guinea worm, Dracunculus medinensis. A person becomes infected by drinking water containing water fleas infected with guinea worm larvae, or more rarely by eating a paratenic host that has itself eaten infected water fleas. The worm larvae penetrate the digestive tract and escape into the body where the females and males mate. Around a year later, the adult female migrates to an exit site – usually a lower limb – and induces an intensely painful blister on the skin. The blister eventually bursts to form an intensely painful open wound, from which the long (up to 1 m) white string-like worm slowly crawls over several weeks. The wound remains painful throughout the worm's emergence, disabling the infected person for the three to ten weeks it takes the worm to emerge. During this time, the open wound can become infected with bacteria, leading to death in around 1% of cases.

There is no known antihelminthic agent to expel the Guinea worm. Instead, the mainstay of treatment is the careful wrapping of the emerging worm around a small stick or gauze to encourage its exit. Each day, a few more centimeters of the worm emerge, and the stick is turned to maintain gentle tension. Too much tension can break and kill the worm in the wound, causing severe pain and swelling at the ulcer site. However, oral metronidazole is known to relieve symptoms, especially pain and pruritus, and prevent abscess formation and local inflammation if the worm was broken during treatment.

Dracunculiasis is a disease of extreme poverty, occurring in places with poor access to clean drinking water. Prevention efforts center on filtering drinking water to remove water fleas, as well as public education campaigns to discourage people from soaking their emerging worms in sources of drinking water.

Humans have had dracunculiasis since at least 1,000 BCE, and accounts consistent with dracunculiasis appear in surviving documents from physicians of antiquity. In the 19th and early 20th centuries, dracunculiasis was widespread across much of Africa and South Asia, affecting as many as 48 million people per year. The effort to eradicate dracunculiasis began in the 1980s following the successful eradication of smallpox. By 1995, every country with endemic dracunculiasis had established a national eradication program. In the ensuing years, dracunculiasis cases have dropped precipitously, and 15 previously endemic countries have been certified to have eradicated dracunculiasis, leaving the disease endemic in just four countries: Chad, Ethiopia, Mali, and South Sudan. A record low 15 cases of dracunculiasis were reported worldwide in 2021, and the number dropped to 13 in 2022. If the eradication program succeeds, dracunculiasis will become the second human disease known to have been eradicated, after smallpox.