According to a new computer modeling research study from Northeastern University network scientist Alessandro Vespignani, when it comes to bioterrorist attacks, “diseases have no borders.” Thus, an outbreak of smallpox intended to harm a local population would ultimately affect the entire planet.Vespignani, the Sternberg Family Distinguished Professor of Physics, Health Sciences, and Computer and Information Science at Northeastern, and his team modeled the spread of a hypothetical smallpox virus across the globe and found that even with the most conservative estimates, a small initial attack in the city of London would likely spread to two or four countries before the first cases were even diagnosed, Vespignani said. The results were reported in a paper published Wednesday in the journal Scientific Reports.

Previous research from other groups have claimed optimistic control outcomes by implementing effective containment policies and sufficient vaccine stockpiles. While these conditions may be realistic for many western countries, Vespignani said, the same is not true across all nations. “These papers considered the local dimension of a potential attack,” Vespignani explained. He added that we are no longer limited by local boundaries. The modern transportation system would allow unknowingly infected individuals to travel across the globe well before any local containment policy was considered, he said.

The team recognized that some members of the global population might be immune to the pathogen if they received the smallpox vaccine before it was eradicated in 1977. But while accounting for immunity brings down the number of individual cases, the same number of countries would be affected regardless, according to the model.

Vespignani noted that the doctrine of “mutually assured destruction” should deter even terrorist organizations, which don’t want to bring devastation to their own people. Nonetheless, he warned, the world must still be prepared for such events. His team’s modeling exercise is a step in that direction.

Additionally, with experiments on increasingly infectious pathogens like H5N1 currently taking place in research laboratories, the model is also relevant in the case of an accidental outbreak. The conditions are slightly different in these scenarios, as diagnosis would likely happen much sooner, but at least in the case of an accidental smallpox outbreak, the problem reaches the international scale just as readily as with an intended outbreak.

Vespignani’s team is currently adapting its model to look specifically at H5N1.