Look at the relationships in contagion between the 1918 Influenza and Ebola

If you look to the right of this chart you can see at the bottom the 2-3 rate of the 1918 influenza and the 1-4 rate of Ebola. So, given this similarity Ebola under some circumstance might kill 50 million people like the 1918 influenza did. 

What would prevent this? World Communication and education and treating the fight against Ebola as a World War to keep people alive and to prevent governments from Collapsing throughout Africa and the Middle East.

Which is a the worst threat to the world order right now? ISIS or Putin or Ebola. I think in the long run 1 to 5 years Ebola is the worst threat by far unless Putin releases nukes and ends all life on earth from U.S. and Chinese Doomsday weapons when they are triggered by Putin's nukes.

 

Basic reproduction number

From Wikipedia, the free encyclopedia

Values of R₀ of well-known infectious diseases^[1]

Disease	Transmission	R0
Measles	Airborne	12–18
Pertussis	Airborne droplet	12–17
Diphtheria	Saliva	6–7
Smallpox	Airborne droplet	5–7
Polio	Fecal-oral route	5–7
Rubella	Airborne droplet	5–7
Mumps	Airborne droplet	4–7
HIV/AIDS	Sexual contact	2–5
SARS	Airborne droplet	2–5[2]
Influenza (1918 pandemic strain)	Airborne droplet	2–3[3]
Ebola	Bodily fluids	1–4

In epidemiology, the basic reproduction number (sometimes called basic reproductive rate, basic reproductive ratio and denoted R₀, r nought) of an infection can be thought of as the number of cases one case generates on average over the course of its infectious period, in an otherwise uninfected population.^[4]
This metric is useful because it helps determine whether or not an infectious disease can spread through a population. The roots of the basic reproduction concept can be traced through the work of Alfred Lotka, Ronald Ross, and others, but its first modern application in epidemiology was by George MacDonald in 1952, who constructed population models of the spread of malaria.
When

R₀ < 1

the infection will die out in the long run. But if

end partial quote from:

A virus's basic reproduction number