The life cycle is the weak point. A person who drinks unfiltered water containing copepods carrying larvae develops an infection that takes about a year to mature. The female then migrates to the skin, usually of the lower leg, and forms a painful blister. Immersing the limb in water for relief causes her to release larvae, which are eaten by copepods, closing the loop.
Every intervention targets that loop. Cloth or pipe filters remove copepods from drinking water; treating ponds with the larvicide temephos kills them; and case containment means finding each patient before emergence and keeping the affected limb out of water sources. Reported human cases fell from an estimated 3.5 million in 1986 to fewer than twenty in recent years.
The endgame is harder than the campaign. Infections in dogs, particularly along the Chari River in Chad, have complicated the picture, because a non-human reservoir can maintain transmission where human surveillance alone would suggest success. How dogs acquire the infection, and whether eating fish or amphibian paratenic hosts is the route, is under investigation and is the central open question for certification.