MERS-CoV, The Haj, and the remote chance of a killer global pandemic
It seems to me that the science of epidemiology is a lot like being in shoe sales in a country on the pacific rim. You never know when the other shoe is going to drop, but you know it will. Our species (humans) is numerous, contiguous, and dense (in more ways than one). This means that a highly virulent pathogen could spread across the globe and kill a gazillion people before we could do anything to stop it. Yet, such a thing has not happened in modern times, meaning, since the widespread and easy flux of population provided by the airline industry at several scales of space.
Source: scienceblogs.com