In a second animation, the path of swine influenza H1N1 is traced over time from its origins in the Southeast's hog farms.
"Understanding the importance of long-distance pig transportation in the evolution and spatial dissemination of the influenza virus in swine may inform future strategies for the surveillance and control of influenza," Nelson and her colleagues concluded in their paper.
Want to find out more about where your state's hogs, cattle and sheep are coming from? Check out the U.S. Department of Agriculture's "Interstate Livestock Movements: State-to-State Flows" interactive maps to search by state and animal.
Animations courtesy of Nelson MI, Lemey P, Tan Y, Vincent A, Lam TT-Y, et al.