By JASON PATINKIN, Associated Press

JUBA, South Sudan (AP) — Former US President Jimmy Carter says that Guinea worm disease may soon be eradicated, which would be the most exciting accomplishment of his career, although progress is hampered by ongoing conflict in Mali and South Sudan.

Carter has led a campaign since 1986 through his foundation, the Carter Center, to rid the world of the once-widespread disease. With only 22 cases worldwide last year, they may now be on the cusp of wiping it out forever.

"It'd be the most exciting and gratifying accomplishment of my life," the 91-year-old Nobel Peace Prize winner told The Associated Press on Tuesday. Carter spoke on a call to South Sudan from London, where the former president is visiting. Carter was to address the House of Lords Wednesday to speak about the campaign against the Guinea worm.

Guinea worm is caused by a water-borne parasite that, once ingested, grows over a year inside a person's body into a three-foot-long parasite which burrows out a patient's skin through a painful blister. There is no cure, so infected patients must wait for weeks as the worm is excruciatingly pulled out by being slowly wrapped around a stick.

When the Carter Center began its campaign there were an estimated 3.5 million cases of Guinea worm disease in 31 countries. The 22 cases last year were confined to South Sudan, Ethiopia, Mali, and Chad.

"We've prevented about 80 million people from having Guinea worm, so this is a great accomplishment in itself," he said. "If we keep that up, it'll just be a year or two (before there are zero cases)."

Carter, who was diagnosed last summer with melanoma, a serious form of cancer, in his liver and brain, said he will continue treatment despite multiple scans showing no signs of cancer following treatment. A brain scan in December found no cancer, Carter announced at the time. Carter said Tuesday that a scan last week of his chest and abdomen found the cancer had not returned to those areas either. Cancer-free for now, Carter said he has a "good chance" of outlasting the last Guinea worm. "That's my ultimate goal," he said.

There is no cure for Guinea worm, so Carter's efforts to eradicate that disease involve deploying thousands of workers and volunteers to remote villages to find patients and stop the disease's spread. When they find someone infected, they treat the blister and prevent the person from entering water sources where the exiting worm can release its eggs and contaminate a community's water supply.

"Despite the fact that we only have a few cases, we have to monitor thousands of villages to make sure that every time somebody does have Guinea worm, that we can isolate them, keep them out of the water so Guinea worm process won't repeat itself among other people," Carter explained. The Carter Center also teaches people in endemic villages to strain their water using cloth or a special pipe filters to prevent ingesting Guinea worm larvae.

Carter warned that obstacles remain to complete eradication, which occurs after three consecutive years with no cases found, according to the World Health Organization.

"We have two major challenges. One is there's violence still in South Sudan, as you know, and also in Mali, and we have a Guinea worm outbreak among dogs in Chad," Carter said.

South Sudan, which had five cases last year, is stuck in a two-year civil war and the fighting has frequently disrupted delivery of aid. Mali, which also had five cases in 2015, faces an Islamist insurgency following a 2012 coup.

"Despite the violence that had broken out...they've had a dramatic reduction in their number of guinea worm cases, around 85 percent down compared to 2014, and that's the most encouraging thing" Carter said. "So that shows I think the heroism and the dedication of the people who are working in various villages in South Sudan."

If stopped, Guinea worm would become the first parasitic disease and the second human disease after small pox to be eradicated.

"It's a very exciting, challenging, worldwide combat that not many people know about," said Carter. "It's crucially important to the people that have a horrible worm coming out of their body."