By Astrid Zweynert

LONDON (Thomson Reuters Foundation) - Mali has eliminated Guinea worm disease bringing the world a step closer to eradicating the debilitating parasitic disease that is now only endemic in three African countries, the U.S.-based Carter Center said, citing provisional government figures.

Guinea worm afflicted 3.5 million people 30 years ago but is now only endemic in South Sudan, Chad and Ethiopia, where there were 16 reported cases last year, according to the organization set up by former U.S. president Jimmy Carter and his wife.

Last November, the doctor leading the fight against the disease which can cause worms up to a meter long to grow before emerging through the skin, said the world had never been so close to eradicating Guinea worm.

Carter, 92, has made the fight against the disease for which there is no vaccine or medical treatment, a cornerstone of his organization's work.

"The progress we have seen in restricting Guinea worm disease to these few cases in only three countries is testament to the dedication of people in endemic areas to caring for their health and that of their communities," said Dean Sienko, the Carter Center's vice-president of health programs.

The disease can cause fevers, blisters and extreme pain when the worms emerge from the body. It is spread by drinking unboiled stagnant water containing the larvae.

The Carter Center said the disease is being wiped out through community programs that show people how to filter drinking water and prevent contamination.

Although the global number of cases has declined, one worm can cause 80 new cases after its incubation period of 10-14 months, so keeping cases low signals the battle is being won.

The World Health Organization (WHO) has said the battle to eradicate Guinea worm is being hampered by insecurity in countries where the disease is endemic with health workers and volunteers often venturing hundreds of miles into lawless areas.

Another challenge is that dogs - mainly in Chad, but also in the other countries - are picking up Guinea worm infections too.

(Reporting by Astrid Zweynert; Editing by Katie Nguyen. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, which covers humanitarian news, women's rights, trafficking, property rights and climate change. Visit news.trust.org to see more stories)