Dracunculiasis is caused by the nematode Dracunculus medinensis, or Guinea worm. It causes chronic cutaneous ulcers with protruding worms in rural Africa. It was a major cause of disability, but recent control efforts have been remarkably successful. Annual incidence has decreased from about 3.5 million cases in the late 1980s to total reported cases of 126 in 2014 and 22 in 2015. However, progress has recently stalled, with 25 reported cases in 2016 and 30 in 2017; these cases were all from South Sudan, Mali, Chad, and Ethiopia. Remarkably, in 2018, a single case of dracunculiasis was confirmed in Angola. Of concern, infection has also been identified in domestic dogs and cats in endemic countries.
Infection occurs after swallowing water containing the infected intermediate host, the crustacean Cyclops (known as copepods or water fleas). In the stomach, larvae escape from the copepods and migrate through the intestinal mucosa to the retroperitoneum, where mating occurs. Females then migrate to subcutaneous tissue, usually of the legs, over about a year (eFigure 35–38). A subcutaneous ulcer then forms (eFigure 35–39). Upon contact with water, the parasite discharges large numbers of larvae, which are ingested by copepods. Adult worms, which can be up to a meter in length, are gradually extruded. Worm death and disintegration in tissue may provoke a severe inflammatory reaction.
Life cycle of Dracunculus medinensis (guinea worm). Humans become infected by drinking unfiltered water containing copepods (small crustaceans) that are infected with larvae of D medinensis. Following ingestion, the copepods die and release the larvae, which penetrate the host stomach and intestinal wall and enter the abdominal cavity and retroperitoneal space. After maturation into adults and copulation, the male worms die and the females (length: 70–120 cm) migrate in the subcutaneous tissues toward the skin surface. Approximately 1 year after infection, the female worm induces a blister on the skin, generally on the distal lower extremity, which ruptures. When this lesion comes into contact with water, a contact that the patient seeks to relieve the local discomfort, the female worm emerges and releases larvae. The larvae are ingested by a copepod and after 2 weeks (and two molts) have developed into infective larvae. Ingestion of the copepods closes the cycle. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.)
Worm blister caused by the head of a female guinea worm (Dracunculus medinensis). A: The female Guinea worm induces a painful blister. B: After rupture of the blister, the worm emerges as a whitish filament in the center of a painful ulcer, which is often secondarily infected. (Reproduced with permission ...