It all starts with a sip of water that’s contaminated with the worm’s larvae. Inside a human host, the larvae punch through the digestive tract, entering into the body cavity to quietly grow. Within a few months, the male and female worms meet and mate. Then the males die off. The surviving female worms mature, reaching 60 to 100 centimeters (2 to 3 feet), and migrate into the victim’s muscles. About 10 to 14 months after that tainted drink, the female worms burn through the skin by oozing acid, creating a searing blister. This can happen anywhere in the body, but it’s usually in the legs or feet.

Not coincidentally, dunking the blister in water eases the pain—and gives the female worm the opportunity to burst out of the wound and spew a milky slurry containing millions of larvae, which starts the cycle all over again. From there, the victim can slowly try to pull the worm out. But yanking too quickly could break the thin parasite (measuring only 1 to 2 mm wide), which could cause an infection. Instead, it has to be slowly extracted, usually by winding the end around a piece of gauze or twig and turning it a few times each day. The process often takes weeks.

The nasty culprit here is the Guinea worm (Dracunculus medinensis). The infection is called dracunculiasis, Latin for “afflicted with little dragons,” after the burning blisters they create on their way out.

In 1986, there were an estimated 3.5 million cases of dracunculiasis in 21 countries on two continents. But today, we’re on the cusp of completely eradicating the fiery infection, thanks in large part to work by the Carter Center, a philanthropic organization co-founded by former President Jimmy Carter that led the charge to eliminate Guinea worms.

Last week, the young country of South Sudan announced that it hadn’t had a case in 15 consecutive months—longer than the worm’s life cycle. And the World Health Organization has certified 199 countries, territories, and areas as dracunculiasis free. That means that in 2017, there were just 30 cases worldwide—15 in Chad and 15 in Ethiopia.

“The people and government of South Sudan have achieved a great milestone in the worldwide effort to eradicate Guinea worm disease,” Carter said in a statement . “South Sudan’s success shows that people can collaborate for the common good. We look forward to certification by the WHO in the next few years that South Sudan has won the battle against this ancient scourge. We are within reach of a world free of Guinea worm disease.”

The Carter Center and other groups have worked to eliminate the worm by distributing cloth water filters, advocating for safe drinking water sources, treating victims, applying insecticide to contaminated ponds, educating communities about transmission, and monitoring cases.

There were also complex environmental and political challenges to the eradication efforts. For instance, Carter personally negotiated a 1995 ceasefire agreement during Sudan’s civil war that allowed health workers to carry out their intervention efforts. South Sudan, which gained independence in 2011, prevailed despite long rainy seasons and high incidence rates.

Health advocates are continuing their work in Chad and Ethiopia, including tracking infections in dogs.

If they can wipe out the few remaining case counts, dracunculiasis will be the second human disease eradicated globally. The first was smallpox, declared eradicated in 1980. Rinderpest, a deadly virus in cattle, was eradicated in 2011.