If you look back on flu panic situations, swine flue many years ago, SARS a couple years ago, more recently bird flu and now bird/swine flu.
I once heard a prominent scientist discuss the plague. What he pointed out was a kind of interesting Darwinian theory on pandemics. His concept was that one needs conditions where the immune systems of a large concentrated population are weakened by drought or famine (or war). This then allows for a lot of theme & variation among mutating illnesses so that a "superior" (i.e. highly contagious and particularly nasty) form of illness to be created by mother nature.
In thinking about this and that SARS was from China in 2003, I really have to wonder about how well the Chinese people are doing under the great industrialization.
I also wonder what will happen to China if they are ground zero for the pandemic. It could be an interesting internal revolution in terms of crowd control followed by an interesting revolution in terms of high economic growth expectations not being fulfilled because there are few people to build the infrastructure and man the factories.
There's probably something to that. The Justinian Plague began during the Dark Ages.