An Ebola epidemic in Guinea, Liberia and Sierra Leone is out of control and requires massive resources from governments and aid agencies to prevent it from spreading further, medical charity Medecins Sans Frontieres (Doctors Without Borders) said on Monday.

The death toll has hit 337 since February, the U.N. World Health Organization said last week, making it the deadliest outbreak since Ebola first emerged in 1976.

The disease has not previously occurred in the region and local people remain frightened of it and view health facilities with suspicion. This makes it harder to bring it under control, the charity said in a statement.