Three people have been diagnosed with Guinea worm disease in South Sudan, just four months after officials announced the end was in sight for a neglected tropical disease (NTD) that once devastated the country.

Guinea worm disease once infected hundreds of thousands of people in South Sudan, but the NTD had not been diagnosed there since December 2016 and officials believed then that it was about to be eliminated.

Dr. Riek Gai Kok, South Sudan’s health minister, said that to keep it contained, an emergency surveillance team has been sent to the town of Rumbek, where two teenage girls and a 23-year-old man were identified as the patients, according to The Telegraph.

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People become infected by Guinea worm disease when its larvae infects drinking water. After larvae is ingested, they grow into their full size of two or three feet inside the body.

The worm then commonly causes a painful blister on the infected person’s feet or legs to come out of the body, which is painful enough to keep people bedridden for three months, according to The Telegraph.

People often soothe their infected foot or leg into water to ease the pain, but this further contaminates the water as the wound releases larvae into it and creates a vicious cycle of infection, according to Centers for Disease Control and Prevention (CDC).

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While the reporting of new cases is upsetting, aid workers remain optimistic.

"I am totally convinced that the eradication of Guinea worm disease in this country is on the horizon if the right measures are put in place," Moses Nganda, the WHO’s South Sudan representative, told the Sudan Tribune.

South Sudan was once plagued by this disease, and its near-eradication is considered a great success.

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In 1986, there were an estimated 3.5 million cases of Guinea worm disease, across 21 countries in Africa and Asia, according to The Carter Center.

In 2017, there were 30 cases reported in only Chad and Ethiopia, thanks to eradication efforts like the one led by The Carter Centre.

To date, the only disease to be eradicated is smallpox, but diseases like polio are 99% of the way there and the World Health Organization has set the goal to eliminate Guinea worm and other NTDs by 2020.