No word yet which strain of Ebola is loose. Some of the more nasty strains have a mortality rate higher than 90%. The 70% figure sounds like an average.
Oddly, a rate over 90% can stop the spread of a disease if people die quickly and it burns itself out.
If it had a 50% rate then it would consume all medical resources for care of the recovering patients...there would be few resources available to try to stop the spread of the virus.
90% = earlier Ebola epidemics that burned themselves out.
50% = the Black Plague.
10% = the killer flu that went around the world during WW1.
This is the Ebola Zaire strain. Its mortality rate is highly variable, ranging from 44% to 90% in past outbreaks.