Health officials are investigating a new outbreak of the Ebola virus that has killed four people in Sudan.
A team from the World Health Organization (WHO) has traced the outbreak to Yambio, in the Western Equatorial region of south Sudan.
There are 19 probable cases. About 120 people who came into contact with them are being kept under surveillance.
A WHO spokesperson told the BBC the outbreak did not appear to be as virulent as previous ones.
PAST MAJOR OUTBREAKS
1976 - southern Sudan, 117 deaths
1995 - Congo, 280 deaths
2000 - northern Uganda, 173 deaths
2002 - Congo, 100 deaths
Despite earlier reports, it was not thought that a new strain of Ebola was involved.
The Ebola virus in its early stages is hard to diagnose because some of the symptoms, like fever and joint pain, mimic malaria.
Many people go on to develop internal bleeding, a characteristic typical of Ebola, and without medical attention the prospects are bleak.
A crisis group has been set up with aid agencies in the region, in an attempt to curtail the spread.
The biggest recent outbreak was in Uganda four years ago; hundreds died.
The BBC's Karen Allen on the Kenya-Sudan border says the hope is that quick action now will avert a similar crisis in southern Sudan.