December 11, 2013; 9:05 PM ET
The coldest air of the season so far is moving in for the middle of this week around Philadelphia, in the wake of Tuesday's snowstorm. A new storm will move in this weekend. more >
1-3 inches of snow late Saturday morning through Saturday afternoon
The sheer number of people, their interactions with animals and ecosystems, and the increase in international trade and travel are all factors that will likely change the way humanity deals with preventing and treating epidemics, experts say.