At least 10 cases of an Ebola-like virus have been reported in southern Sudan, where four people have died from the infection, the World Health Organization (WHO) said on Friday.

The WHO’s office for southern Sudan said health authorities in Yambio county reported a total of 15 patients suffering symptoms similar to Ebola, which can kill up to 90 percent of its victims.

Laboratory tests conducted in Kenya and at the U.S. Centers for Disease Control and Prevention “confirmed an Ebola-like infection in 10 of the 15 cases,” the WHO said in a statement.

“They both agreed that the virus involved is within the family of Ebola, but they still need to make some genetic sequencing to tell us exactly…we hope to get final confirmation within 48 hours,” Abdullahi Ahmed, head of the WHO’s southern Sudan office, told Reuters.

The WHO said no new cases had been reported for the last three days, with the most recent case reported on May 15.

Two patients are now being cared for in a hospital isolation ward in Yambio, while health workers are following up 102 people known to have had close contact with victims.

“From the data we have, the death rate and the way it is presenting, it seems to be mild,” Ahmed said. “But it was only yesterday that we established our monitoring team and we don’t know the situation in the countryside.”

Ebola starts with a high fever and headache and can lead to massive internal bleeding. It is passed on by infected body fluids and is known as one of the deadliest and most feared diseases in the world.

An outbreak in Congo Republic earlier this year killed more than 120 people. Authorities there said in April that they had almost brought the disease under control.