Humans become infected by drinking unfiltered water containing copepods (small crustaceans) which 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 to 120 cm) migrate in the subcutaneous tissues towards the skin surface .  Approximately one 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 two weeks (and two molts) have developed into infective larvae .  Ingestion of the copepods closes the cycle .