The World Health Organization has ratcheted up the alarm over Africa's Ebola epidemic. More than 900 deaths across Liberia, Nigeria, Guinea, and Sierra Leone mean this is now an "international emergency" that requires an "extraordinary response," reports the BBC. The move is just the third time WHO has made that kind of declaration since putting the language in place in 2007, notes the New York Times. It comes a day after the CDC raised its Ebola alert to the highest level. Developments: