Worrying indeed, but I fear you are greatly underestimating the crisis. The rate of spread is going to go exponential. We have no idea of the real numbers in the epicentre of the current outbreak, but they are likely much, much higher. Now that the virus has reached major cities, and much more mobile populations, and now that it has been admitted it spreads during the incubation period, then it has to go exponential, not linear.

We already know that the guy who flew into Lagos infected at least three people, but they are suspicious of many more. But anyway, lets be ultra conservative and say he just infected two people. And then they each infected just two people (given that you have three weeks to infect before you know you are infected yourself, then it seems an absurdly low number). Then, by the end of August this year we should be somewhere around one and a half billion infected.

The linear model of spread is unrealistic because it assumes that something is going to be limiting the spread - because the infection rate will naturally increase as more people get it, thus going exponential - but in your model something is holding back that increase. In past outbreaks, or in outbreaks of other viruses that are treatable, then there can be retarding factors like that, but Ebola, when given an unlimited amount of fuel (ie. people) has no effective retarding factors other than effective quarantine. The quarantine can be natural (as in isolated villages etc) or man-made. Up until the point that the virus hitched a ride on board an airliner to a major city, such as Lagos, then although it was spreading, there was a natural retardation in the fact that the populations it was spreading through were poor, not very mobile, and confined mostly to that region of west Africa including Guinea, Sierra Leone and Liberia. This meant that although the numbers were rising, they were rising in a slowed manner.

Now, however, the virus appears to be in developed countries. We are seeing the vanguard infected developing symptoms now - but they were likely infected weeks ago. So, considering the average citizen of western countries, especially those in cities, comes into close proximity/contact with hundreds, if not thousands of people per day, then it becomes absurd to believe that the average infected is not going to give it to more than two other people in the three weeks that they are incubating the virus. This is quite apart from anyone they infect whilst they are showing full Ebola symptoms.

This is now about social physics. I will be accused of fear mongering for saying this, but it isn't. It is just looking at the physics of the situation. We can wish it away, or try to believe the downplay of the officials, but this is the nightmare scenario that many people have talked about for decades. In all previous outbreaks there have been retarding factors in the spread. Those are now gone. You can't quarantine something at this point because it would be impossible to figure out who to quarantine. The fact is that the infected are likely all around us right now. I may be infected, you may be infected. We won't know until the obvious symptoms develop, and that could still be weeks away for millions of people.