Follow the money trail to track the disease

It seems that a popular Web site in the United States that tracks the geographical circulation of money could cast new light on predicting where infectious diseases like bird flu might pop up.

Researchers say that like money, diseases are carried by people around the world, so what better way to plot the spread of a potential influenza pandemic than to track the circulation of dollar bills.

The German and U.S. researchers developed a mathematical model of human travel that can be used to plot the spread of future pandemics.

According to Dr Dirk Brockmann, a physicist at the Max Planck Institute for Dynamics and Self-Organisation in Gottingen, Germany, there are some universal rules governing human travel and they can be used to develop a new class of model for the spread of infectious disease.

The research is particularly relevant at present as world health experts fear the H5N1 bird flu virus that has killed at least 82 people in six countries since 2003, will mutate into a highly infectious strain in humans that could cause the next pandemic.

Brockmann says they are now able to plug in the parameter ranges that they think will apply to influenza and then simulate a pandemic that runs through Europe to see what happens.

He says in addition to giving insights into how an infectious disease would spread, mathematical models and computer simulations could help to develop measures to be used against it.

Human movement is a main cause of the spread of infectious disease but with modern-day travel involving boats, planes, trains, cars and other means of transport it is virtually impossible to compile a comprehensive set of data on travel.

The scientists analysed information from www.wheresgeorge.com, an online bill-tracking Internet site.

Users of the site mark their money with the Web site address, register on the site and follow the trail of their money after they spend it.

According to Brockmann, about 50 million banknotes have been registered on the site, and information from the site enabled the researchers to develop a mathematical theory of human travel behavior.

They found that when they compared their results with the traffic flow of aviation networks in the United States, it correlated very closely.

Brockmann says it provided a very good estimate of how humans travel.

He believes their observations in the United States may also be valid for Europe or Canada, in which case models can be developed for the spread of infectious disease that may reveal universal characteristics of modern pandemics.

The findings are published in the journal Nature.