The life cycle runs through the copepod. A person with dracunculiasis develops a blister, usually on the leg, and seeks relief by entering water, at which point the emerging female worm releases larvae. Cyclops copepods ingest the larvae, which develop inside them, and a person who then drinks unfiltered water swallows infected copepods. Stomach acid digests the crustacean and frees the larvae to mature over about a year.
Breaking the chain does not require a drug. There is no vaccine and no reliable cure once infection is established; the worm is still removed by winding it slowly onto a stick over days or weeks. Control has instead relied on cloth or pipe filters fine enough to exclude copepods, on treating water sources with the larvicide temephos, and on preventing infected people from entering drinking-water sources.
The campaign has been extraordinarily effective. Reported human cases fell from an estimated 3.5 million a year in the mid-1980s to a handful annually, and Guinea worm is a candidate to become only the second human disease eradicated. Infections in dogs, particularly in Chad, are the principal remaining obstacle.