A guinea worm is a parasitic roundworm that grows inside the human body for about a year, then slowly emerges through a painful blister in the skin. The female worm can reach up to 3 feet (1 meter) in length. Once one of the most widespread parasitic diseases in the world, guinea worm disease has been driven from an estimated 3.5 million human cases in 1986 to just 10 in 2025, putting it on the brink of being only the second human disease ever eradicated.
How People Get Infected
Guinea worm infection starts with contaminated drinking water. Tiny aquatic crustaceans called copepods, sometimes described as “water fleas,” live in stagnant ponds and other surface water sources. These copepods are nearly invisible to the naked eye, and some carry guinea worm larvae inside them. When a person drinks unfiltered water containing infected copepods, stomach acid dissolves the copepods and releases the larvae into the digestive tract.
From there, the larvae penetrate the intestinal wall and migrate into the body’s connective tissues, where they mature and mate over the next 10 to 14 months. The male worm dies after mating. The female continues growing, eventually reaching her full length of up to one meter, and migrates toward the surface of the skin, typically in the lower legs or feet.
What the Symptoms Feel Like
For most of that year-long incubation period, an infected person has no symptoms at all. The trouble begins when the mature female worm, now full of larvae, is ready to emerge. A few days to hours before she breaks through the skin, the area becomes swollen and painful, and fever may develop. A fluid-filled blister forms, usually on the foot or lower leg, and the burning sensation drives people to submerge the affected area in water to find relief.
That impulse is exactly what the worm exploits. When the blister contacts water, it ruptures, and the worm expels a milky cloud of hundreds of thousands of larvae into the water source, starting the cycle over again. The worm then emerges slowly as a thin, whitish filament from the center of a painful ulcer. This emergence takes anywhere from one to three weeks, and the open wound almost always develops a secondary bacterial infection that makes the pain and inflammation worse.
Removing the Worm
There is no vaccine for guinea worm disease and no medication that kills the parasite inside the body. The only treatment is physical extraction: slowly winding the emerging worm around a small stick or piece of gauze, a few centimeters at a time. Sometimes the entire worm comes out within a few days, but the process usually takes weeks.
Patience during extraction is critical. If the worm breaks, the portion left inside the body triggers intense inflammation and a high risk of serious bacterial infection. A broken worm can extend the period of disability from weeks to months. In the worst cases, the worm migrates into a joint space, and the resulting infection can lock the joint permanently, causing lasting disability. Even when extraction goes smoothly, the open ulcer leaves a person unable to walk, work, or farm for weeks, which has devastating economic consequences in the rural communities where the disease persists.
How Close the World Is to Eradication
Guinea worm is poised to become the first parasitic disease ever eradicated and the first disease eliminated without a vaccine or medical treatment. The global eradication campaign, led by the Carter Center alongside the World Health Organization and other partners, relies entirely on changing behavior and cleaning up water sources. The core interventions are straightforward: households in affected areas receive fine-mesh cloth filters to strain copepods out of drinking water, and individuals who work away from home get portable pipe filters that function like straws, filtering water as they drink. In areas where water sources are known or suspected to be contaminated, a larvicide called temephos is applied monthly to kill infected copepods.
In 2024, 15 human cases were reported worldwide, along with 664 animal infections. As of mid-2025, transmission continues in six countries: Angola, Cameroon, Chad, Ethiopia, Mali, and South Sudan.
The Dog Problem
Since 2012, a complication has threatened the final stretch of eradication. Dogs, and to a lesser extent cats and baboons, have been found carrying guinea worm infections. In Chad and Cameroon especially, large numbers of infected dogs are contaminating water sources, driving transmission to other dogs, occasional cats, and a small number of humans. Stopping transmission in dogs has become the eradication program’s primary focus.
The leading theory is that dogs become infected by eating raw fish or fish entrails containing guinea worm larvae. In response, Chad launched educational campaigns in 2013 urging people to bury fish entrails rather than leaving them where dogs can scavenge. Starting in 2014, dogs showing signs of infection were tethered to prevent them from entering water sources. That approach has expanded significantly: since 2022, all dogs in any village that has reported even one dog infection are tethered during peak transmission season. Ethiopia pioneered proactive dog tethering in 2018, and the practice has since been adopted in Chad, Mali, Cameroon, and Angola.
Eradication programs have also turned to satellite technology, using remote sensing since 2022 to identify new water sources that need larvicide treatment. Angola offers a cash reward equivalent to $450 for reporting a human or animal infection, creating a financial incentive for surveillance in remote communities. These layered strategies reflect how close the campaign is to finishing the job, and how much the final cases depend on controlling animal transmission rather than human behavior alone.