A recent article in Nature (“The Scaling Laws of Human Travel“) claims that the flow of money may provide a good model of how diseases spread in modern society. Previous models of how pandemics generally thought that the dispersion would occur slowly over a contiguous geographic region. As air travel becomes more and more common (and inexpensive), we may see contagious illnesses jump between countries or even continents. The MedPage Today blog offers a nice summary of how tracking dollar bills on the Internet became feasible means to model the spread of disease.
The model is based on an analysis of data collected by a popular Internet game — found on the Web site www.wheresgeorge.com — in which participants enter the serial numbers of bills in their possession.
Over time, as different people enter the same bill, the game builds up a picture of how the money is moving, said Dirk Brockmann, Ph.D., of the Max Planck Institute for Dynamics and Self-Organization here.
But since paper money — like viruses — travels with people, the game also allowed the researchers to model how humans move through the world, without actually tracking them, Dr. Brockmann said
“The enormous amount of data, as well as the geographical and temporal resolution of bill-tracking, allows us to draw conclusions about the statistical characteristics of human travel,” he said.
Historically, pandemics have moved relatively slowly, because human travel was limited. The 14th century pandemic of bubonic plague – the Black Death — took three years to hit the entirety of Europe, moving from south to north with an average rate of spread of slightly more than a mile a day.
“But today people move great distances in short time periods, as well as short distances, and they use variable means of transportation,” said co-author Lars Hufnagel, Ph.D., of the Kavli Institute for Theoretical Physics at the University of California in Santa Barbara.
“We can expect that future pandemics will spread according to other rules, and more quickly,” he said.
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