epidemiology - How is it possible to even hope for an ebola epidemic of this current size to remain contained to a relatively small part of Africa?

As of 2014-09-14 at least 5347 cases of ebola have been identitied. Some estimates are much higher. While experts are sounding the alarm to try to get sufficient resources to contain the outbreak, some people are also speaking very hopefully about containment to roughly the current affected area. This article puts the risk of the outbreak reaching the United States as low as 3%. I'm not an expert in the field, but it seems like there are almost countless ways in which an increased number of cases increases the risk of further exponential growth. It's encouraging to hear that in countries with better healthcare, death rates would likely be much lower, but at this point, isn't it inevitable that the outbreak will run its course as a global pandemic?

For example, which of these possibilities is just my imagination, or likely so improbable that we don't need to worry about it?

1. 
   

   Scared carriers not yet showing symptoms sneak or force their way across boarders to unaffected regions.

   
   


2. 
   

   Objects, food, or water touched by the infected go unnoticed until they end up leaving the containment zone.

   
   


3. 
   

   If it can jump from bats or monkeys, thousands of infected humans increase points of contact to create vectors into other species, perhaps one that will travel unnoticed far beyond the containment zone.

   
   
   


4. 
   

   After months of the same security precautions day in and day out, airport checkpoints, and other points of entry become lazy, and let infected through.

   
   

With numbers as high as they are, and possibly higher than we even know, is this really containable at all?

Answer

This is too long for a comment, so my thoughts about this here. The CDC Director said a few days ago after a visit in Africa "The window of opportunity is closing".

1. 
   
   

   This can happen. However, you are not getting contagious unless you show symptoms. This is different in other diseases like chicken pox or measles where you spread the virus before showing symptoms. So there has to be a lot of awareness. Also doctors need to be very careful with patients showing these symptoms. This is most likely one of the main reasons for the wide spreading of the disease.

   
   


2. 
   

   Same problem as in 1. Theoretically this is easy to prevent, but in a situation of chaos this can cause problems. But since infected people which show symptoms will not handle large amounts of food, this is most likely less of a problem.

   
   


3. 
   

   Every crossing of a species-barrier is a rare event. Double-crossings are even less likely. So I don't think this is a problem. Besides this, we already have to independent Ebola outbreaks which has never happened before. One is the one in West-Africa, the other one is happening in the Democratic Republic of Congo. Both are independent cross-overs.

   
   


4. 
   

   This can cause problems. The advantage of the first world is that we have functional health care systems. They allow better care for the persons and also better isolation of contact persons. I think it is unlikely that it would spread widely. The perspective will be different, if the virus makes the jump into the densely populated regions in South-East Asia. There a lot of people live closely together, this can cause real problems. Fortunately for us the virus is not highly contagious. To infect yourself you need unprotected contact to the body fluids (blood, stool, feces, sweat etc.) of infected persons.