BARCELONA, Spain (AP) — Three new cases of Guinea worm have been discovered in South Sudan, setting the country back in its efforts to eradicate the debilitating disease.

The World Health Organization says the cases were found among cattle-keepers in Rumbek. South Sudan's health minister, Dr. Riek Gai Kok, says teams have been sent to carry out community-based surveillance.

South Sudan had no reported cases in 2017, a rare success in the young nation deep in a five-year civil war.

Contracted by drinking infected water, Guinea worm affects some of the world's most vulnerable people. Only Chad and Ethiopia had reported cases last year.

The disease only 30 years ago affected 3.5 million people a year in 21 countries across Africa and Asia.

Only one human disease has ever been successfully eradicated: smallpox.