ATLANTA -- South Sudan has gone 15 months without a single reported case of Guinea worm disease, the nation's health minister said Wednesday, suggesting a major victory for global health officials trying to eliminate the painful affliction.

"To us as South Sudanese, we feel we have contributed to the common cause of humanity today, that we have played our part in realizing the dream of ridding the world of this debilitating disease," Dr. Riek Gai Kok said in announcing transmission had been stopped in his country.

The Carter Center, one of the organizations leading global eradication efforts, said only one case of Guinea worm has been reported so far in 2018 in Chad, but cautioned that those numbers were preliminary and would likely rise. The centre said 30 cases were reported last year in isolated areas of Ethiopia and Chad, a real achievement for efforts to eradicate a disease that only 30 years ago affected 3.5 million people a year in 21 countries across Africa and Asia.

Contracted by drinking infected water, Guinea worm disease affects some of the world's most vulnerable people. The 3-foot-long (meter-long) worm is asymptomatic and incubates in people for up to a year before painfully emerging, often through extremely sensitive parts of the body.

Dr. Kok said that in South Sudan the disease would often strike and debilitate entire communities simultaneously, leading to problems with food security and productivity.

Unlike other diseases that are controlled by medicines or vaccines, Guinea worm can be eradicated through education, by training people to filter and drink clean water.

Former U.S. President Jimmy Carter called South Sudan's progress a "great milestone" in the worldwide eradication effort.

"South Sudan's success shows that people can collaborate for the common good," Carter said in a statement. "We are within reach of a world free of Guinea worm disease."

South Sudan was one of nine countries still affected when its eradication program began in 2006. At the time, the disease was endemic in more than 3,000 villages, and the country tallied more than 20,500 cases.

South Sudan's progress against Guinea worm is being touted as one of the few successes to emerge from the young nation while it battles a five-year civil war, starvation and human rights atrocities.

Craig Withers, senior director of international support at the Carter Center, said working in a conflict zone like South Sudan brings unique challenges.

"The history of the program is that we are constantly moving our staff in and out of areas as they open up or violence erupts," he said.

Withers said that co-operation with local communities was essential to the success and safety of the program.

The global campaign to wipe out Guinea worm was launched by the World Health Organization and the U.S. Centers for Disease Control and Prevention. Jimmy Carter has led these efforts since 1986, when the Carter Center and UNICEF joined the campaign.

Only one human disease has ever been successfully eradicated: smallpox. As with Guinea worm, there is also a continuing effort to eradicate polio, but such efforts often face their greatest obstacles in the last phase of stopping the disease.