member of the phylum Nematoda. The guinea worm, a common parasite (parasitism) of humans in tropical regions of Asia and Africa, has also been introduced into the West Indies and tropical South America. A variety of other mammals are also parasitized by guinea worms. The disease caused by the worm is called dracunculiasis.

The female grows to a length of 50 to 120 cm (about 20 to 48 inches), while the male (which is rarely found because it dies upon mating within a human or other host) measures only 12 to 29 mm (about 0.5 to 1.1 inches). Both sexes live in the connective tissue of various organs of the host. Females may live for 10 to 14 months. The female bores close to the skin surface, at which point a blister develops and finally bursts. Millions of larvae are released with the blister fluid. If the larvae are discharged into a watery medium and are eaten by Cyclops, an aquatic crustacean, they develop in the crustacean's body into larvae capable of infecting human beings.

The human being becomes infected by drinking water containing the barely visible flealike crustacean containing the worm larvae. Gastric juices kill Cyclops, and the guinea worm larvae then bore from the human host's intestinal tract into blood vessels; they are carried to connective tissue areas, where they soon develop into adults. Adult worms slowly emerge from blisters, especially on the victim's legs or feet. When the victim enters a pond, stream, or other water, the released larvae are eaten by the crustaceans, to continue the cycle.

For humans the disease dracunculiasis can be extremely debilitating and painful, with worms slowly emerging from open blisters. The open blisters are also a common point of entry for other infections, such as tetanus. Several thousand people are currently infected by guinea worms; however, this number is declining.