1a and 1b. Humans become infected by drinking water containing microcrustaceans (copepods) that are infected with larvae of D. medinensis or eating undercooked fish harboring the larvae.

2. After ingestion, the copepods die and release larvae, which penetrate the stomach and intestinal wall and enter the abdominal cavity and retroperitoneal space.

3. After larvae mature into adults and copulate, the male worms die, and the females migrate in the subcutaneous tissues toward the skin surface. About 1 year after infection, the female worm induces an indurated papule (blister) on the skin, usually on the distal lower extremity. The papule eventually ulcerates.

4. When this lesion comes into contact with water (patients typically immerse the affected extremity in water to relieve the intense discomfort), the female worm emerges and releases larvae.

5. Larvae are ingested by a copepod.

6. After 2 weeks, larvae become infective. When humans ingest the copepods, the cycle is completed.