By Hayley Peterson

PUBLISHED: 21:48 EST, 24 July 2013 | UPDATED: 22:12 EST, 24 July 2013

A bioterrorism attack could spread to several continents before it is even detected, according to a startling new scientific study. 

The study found that if a small group of terrorists infected themselves with a disease such as smallpox and walked around London, then the pathogens could spread to up to four nations before doctors managed to diagnose it. 

'A deliberate smallpox release is likely to assume an international dimension even before the epidemic is identified,' the researchers wrote in the  study, which was published in this month's Scientific Reports, a trade publication. 

'We show through large-scale individual-based simulations that biological targeted attacks on a single city can result in the presence of exposed individuals in several countries before the health system is aware of the release and the ensuing outbreak.'

Developed nations have contingency plans to contain biological attacks, but the study points out that the pathogens could rapidly overtake less developed nations that don't have the same resources.

'Some of the countries that could be affected may not have health infrastructures able to timely cope efficiently with the emergency dictated by a highly pathogenic virus outbreak,' the study notes.

The researchers who conducted the study recommend that international health organizations better prepare for the possibility of a biological attack that originates in a remote location.

'They need to think about sharing resources,' one of the researchers, Alessandro Vespignani, told Quartz. Vespignani is a health sciences professor at Northeastern University. 

Parts of the study were not published due to international security concerns. 

'According to the comments of biosafety reviewers, we have removed quantitative data on risk probability and outbreak size in different scenarios,' the researchers wrote. 'Those additional outputs can be shared with government officials and biosecurity researchers upon request.'