Since 1976, Ebola virus disease outbreaks have primarily occurred in eleven countries: Democratic Republic of the Congo, Gabon, Guinea, Liberia, Mali, Nigeria, Republic of Congo, Sierra Leone, Sudan and Uganda. Although it is generally rare, it is often fatal, with death rates ranging from 25 to 90% in past outbreaks (average case fatality rate, 50%). No treatment or vaccine is currently approved, but there are several promising vaccines and treatments under development.