You're comparing a fairly stable, relatively well understood danger with a rapidly growing, less well understood danger. Elsewhere in this discussion, someone

You're comparing a fairly stable, relatively well understood danger with a rapidly growing, less well understood danger. Elsewhere in this discussion, someone quotes a CDC estimate that by the end of the year the number of ebola cases could reach 100k to 1.4 million. Taking the lower end of the range, that's 100k new cases in 3 months, so the number of cases grows by a factor greater than 10 in 3 months.