The health authorities in the Democratic Republic of Congo say 55 people are feared to have died from Ebola.
The government has confirmed that 28 of those deaths were definitely from the virus.
Vaccines and experimental drugs are being used to help limit the spread but the authorities expect the number of cases to increase.
Two treatment centres in North Kivu province are nearly at capacity and a new centre is about to be built in neighbouring Ituri province.
Health workers are trying to monitor more than 1,500 who have been in contact with Ebola patients – but the task is challenging due to outbreaks of violence in the eastern region, where many rebel groups operate.