Health workers celebrated the remarkable step towards eradicating the flesh-burrowing guinea worm in South Sudan.
The World Health Organization called the results "remarkable", and the progress comes despite a civil war raging in South Sudan for the past 18 months.
In the mid-1980s, 3.5 million people in 20 countries were infected with the water-borne parasite that causes agonizing pain and leaves sufferers unable to function for months. Now, apart from South Sudan, guinea worms exist only in Chad, Ethiopia and Mali.
"The task is not yet complete...until there are zero cases of guinea worm throughout South Sudan, and the country is certified guinea worm free," South Sudan's health ministry said in a statement, announcing cash rewards for anyone reporting a case to medics.
"Eradication of this painful scourge is within our reach... let us work together in the final push."
South Sudan's health ministry said that in 2006 there were over 20,500 recorded cases, while there has now been no recorded case since October 2014.
The Carter Center - the not-for-profit organization founded by former US president Jimmy Carter - has been working in South Sudan since 1989 to exterminate the worm once and for all. The center said it was "thrilled" at the news.
If the campaign succeeds, guinea worm will become the first parasitic disease to be eradicated and only the second human disease to be wiped out worldwide after smallpox in 1979.
In 2014, South Sudan reported the highest number of cases globally, a total of 70, far higher compared with the only other three countries left with the worm - Mali where there were 40 cases, Chad where there were 13 and Ethiopia where there were just three.
Also known as dracunculiasis, from the Latin for "little dragons", the worm is a particularly painful water-borne parasite that can leave people weakened and sick for months every year.
After about a year feeding inside the body, the long white worms dig through the body towards the skin, releasing chemicals to burn the flesh and then spewing thousands of larvae as they exit.
Although there is no direct treatment, the breeding cycle can be broken by making sure people do not wash in sources of drinking water while the worm is emerging from the skin.
Worms mainly exit from the legs and arms but affected communities say they have been known to emerge from the head, sexual organs and even the eyes.
They must be slowly teased out by wrapping the wriggling worm around a stick - the reported origin for the medical symbol of a snake coiled around a staff.