More than 1,000 cases have been reported in Guinea, Sierra Leone and Liberia since symptoms were first detected in the region four months ago.
The death of a Liberian man hospitalized in Lagos with the virus is raising fears that the latest outbreak could spread into Nigeria, Africa's most populous country. One of Liberia's most prominent doctors has also died from the virus, and an American doctor and aid worker are now infected.
Doctors Without Borders said the way the virus has spread is unlike any previous Ebola outbreaks, raising alarm among health workers.
"Ebola is usually a localized, rural disease, but this outbreak has a broad geographic spread and is reaching cities too," wrote GlobalPost Senior Correspondent Tristan McConnell, who is based in Nairobi, Kenya.
First detected in 1976, the Ebola virus has killed an estimated 1,900 people in the years since. Here are the seven deadliest Ebola outbreaks in history, according to figures from the World Health Organization and the Centers for Disease Control and Prevention.
1. Guinea, Sierra Leone and Liberia, 2014 (660 deaths)
2. Democratic Republic of the Congo (then Zaire), 1976 (280 deaths)
3. Democratic Republic of the Congo, 1995 (250 deaths)
4. Uganda, 2000 (224 deaths)
5. Democratic Republic of the Congo, 2007 (187 deaths)
6. Sudan, 1976 (151 deaths)
7. Republic of Congo, 2003 (128 deaths)