A rare tropical disease called Guinea worm is closer to being eradicated, according to former President Jimmy Carter and other experts.
There are now only 542 known cases of Guinea worm left worldwide, as of 2012, representing a 48% decrease from 2011, officials said Thursday at a news conference.
"We cannot rest until we get and contain the very last case," said Dr. Donald R. Hopkins, affiliated with the Carter Center in Atlanta, which has been instrumental in the effort to wipe out Guinea worm.
The World Health Organization this week said in a report that Guinea worm, also called dracunculiasis, has a global eradication target for the year 2015.
So far, only one disease has reached the status of worldwide eradication since 1980: smallpox.
In 1986, when the Carter Center began leading its international campaign against Guinea worm disease, there were 3.5 million cases in 21 countries.
South Sudan has the most known cases today, at 521, followed by Chad (10), Mali (7), and Ethiopia (4), according to the Carter Center. These are the only four countries that still have transmission of Guinea worm.
A main obstacle to eradication is that one case of Guinea worm disease, if not addressed quickly, can spread to hundreds more people, Carter said.
Communities that depend chiefly on open water sources like ponds in rural and isolated areas are especially affected, according to the World Health Organization.
The disease gets into the body when people drink contaminated water, which contains water fleas that have ingested Guinea worm larvae. The human stomach kills the water fleas, but not the larvae within. Worms can get through the intestinal wall and move around under skin tissues.