More than 20,000 people likely have been infected by the virus, which so far has killed at least 7,842, the World Health Organization reports.
The epidemic began quietly in rural southeastern Guinea in the last days of 2013. The Ebola virus then raged through Guinea, Liberia and Sierra Leone.
It made forays into Nigeria and Mali, killing more than a third of those it infected, including doctors and caregivers. In its wake, Ebola left behind thousands of orphans, Voice of America reported.
This has been the biggest and most challenging Ebola outbreak since the virus was identified in 1976, according to WHO.
More than 20 outbreaks in other parts of Africa have been much more easily contained, said Dr. Tom Kenyon, who heads the Center for Global Health at the US Centers for Disease Control and Prevention in Atlanta, Georgia.