Former President Jimmy Carter says Guinea worm disease cases were cut to less than 600 cases in 2012, marking significant progress in eradicating the parasitic infection.

The Atlanta-based Carter Center released the provisional numbers Thursday during the former president's first social media press conference.

The only other human disease to be eradicated is smallpox.

Carter says challenges remain, including security concerns in nations where the disease persists. Carter says sustained monitoring is crucial because one case in a village can spread if not addressed quickly.

Guinea worm is spread by drinking contaminated water. In 2011, there were 1,058 cases reported. There were just 542 in 2012.

The Carter Center says there were 3.5 million Guinea worm cases in 21 countries when it began leading eradication efforts in 1986.