The original claim would be hyperbolic, except that someone killed in a car crash doesn't increase the risk to other people on the road, but an Ebola infection certainly does. In the mathematics of exponential increase, a small initial amplification factor can produce very impressive results in a short time. Consider the hypothesis that just 1% of Ebola sufferers infect other people. Using this well-established mathematical method:

y' = y (1+p/100)^t

y = infected population % at time zero.

y' = infected population % at time t.

t = time in consistent units

p = percentage increase for one unit of time

So, if it takes a week for the infected population to increase by 1%, then:

http://i.imgur.com/TDPd7ug.png

IOW if after a week the infected population has increased by 1%, after a year (52 weeks) the infected population has increased by 67%. After 2 years (104 weeks) the infected population has increased to 281% of the original. And so forth.

This isn't true for car crashes, and the above is what is meant by an "exponential increase".