The most relevant features of NECSI’s model to the current crisis is the critical threshold of connectedness at which a virulent strain can spread out of control.
Even if a system seems stable, it may only take a few more routes of travel to trigger secondary outbreaks.
“It wouldn’t take much for the current Ebola outbreak to spread to more countries or continents,” says NECSI president Yaneer Bar-Yam. “It only takes one infected individual making it through an airport checkpoint.”
When it comes to pandemics, it only takes a little global connectedness to trigger a cascade of infections. The outbreak of Ebola raging in West Africa— labeled a Public Health Emergency of International Concern by the World Health Organization—echoes a scenario mapped out by NECSI in 2006. In a computer simulation of pathogens and hosts, long-range routes of transmission — most prominently, international air routes — can allow the deadliest viral strains to outrun their own extinction, and in the process kill vastly more victims than they would have otherwise.
In an evolutionary model accounting for spatial distribution, a pathogen like the Ebola virus can cause its own demise by killing all the hosts in its immediate vicinity. If there is no one left alive to infect, a viral strain will die off. Successful pathogens leave their hosts alive long enough to spread infection. Typically, the most virulent mutations burn themselves out, and a stable balance is achieved between host and pathogen. But avenues of long-range dispersal break this pattern.