The worm Dracunculus medinensis is caught by swallowing water contaminated by microscopic crustaceans (copepods – water fleas) that contain the worm larva. In the stomach these are released, burrow through the stomach wall into the bloodstream, and migrate to the fat under the skin where they mature. After mating the male worm dies, but the mature female worm, which may be 60 to 80 cm. long, moves to the skin surface where it forms a sore, and through this discharges eggs every time the skin comes into contact with water. The eggs are then swallowed by the copepods where the cycle starts again. The worms eventually die and emerge through the skin sore, or occasionally remain under the skin. The full cycle takes 9 to 14 months.
Patients experience generalised itching, fever, shortness of breath and nausea when larvae are in the blood. Redness, burning and itching occurs at the site of skin sores, usually on the foot or leg. After the worm dies a red, tender ulcer forms.
Smears from skin sores show eggs when examined under a microscope to confirm the diagnosis.
The patient should rest with affected leg elevated. Worms can be individually removed by exposing one end and then slowly drawing them out a centimetre at a time over several days. Medications cannot kill worms, but may encourage them to be expelled through a sore. Secondary bacterial infection of an ulcer can spread to the surrounding skin (cellulitis). Abscesses can form under the skin (particularly if a worm is broken during removal), in joints or rarely in other organs that are reached by worms.
The ulcers heal after a month or two and most patients recover eventually.