1a and 1b. People become infected by drinking water containing tiny crustaceans that are infected with larvae of Dracunculus or eating undercooked fish harboring the larvae.
2. After the crustaceans are swallowed, they die and release the larvae, which penetrate the wall of the stomach and intestine and enter the abdominal cavity. There, larvae mature into adult worms, which then mate.
3. After mating, the male worms die, and the females move through tissues under the skin usually to the lower legs or feet. About a year after people are infected, the pregnant female worm comes to the surface of the skin, creating a blister. The blister causes severe, burning discomfort and eventually breaks open.
4. When people attempt to relieve the burning by soaking their leg in water, the pregnant worm releases larvae into the water.
5. The larvae are ingested by another crustacean.
6. Inside the crustacean, the larvae change into different forms and become able to cause infection. When people swallow the crustaceans, the cycle is completed.
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.