When it comes to the science of surviving a potentially deadly outbreak, there is one question that has always proved particularly tricky for experts.

How do you study the spread of an epidemic, and thus form an emergency plan to ensure the survival of the human race, without putting the population at risk of a real disease?

Researchers have now made an unlikely breakthrough, thanks to a glitch in a fantasy computer game. In an online game called World of Warcraft, an unexpected error in the software has provided a ready-made laboratory for studying the effects of an epidemic.

The 6.5 million players who control characters in the role-playing game supplied the necessary element of unpredictable human reactions without any risk to the real world.

The discovery, revealed in next month’s issue of The Lancet Infectious Diseases journal, has been hailed as a significant step forward in understanding how a deadly virus could break out.

“By using these games as an untapped experimental framework, we may be able to gain deeper insight into the incredible complexity of infectious disease epidemiology in social groups,” wrote the authors, Eric Lofgren, of Rutgers University, New Jersey, and Nina Fefferman, of Tufts University, Boston.

And it all happened by accident. In September 2005 what was intended as a minor hindrance for a small group of characters spiralled beyond the control of program-makers into a full-blown epidemic.

A new villain, a winged serpent called Hakkar, originally designed as a challenge for only the strongest characters, started transmitting its “corrupted blood” virus down the ranks until it affected almost every area and every player in the game.

The scientists were able to monitor how quickly the disease spread and where to, while assessing the players’ individual responses to the outbreak. The particular features of the game, such as the many hours players around the world dedicate to it and the emotional investment they put into their online alter egos, offer scientists a tantalisingly close match to real social conditions.

As the virus spread, very real challenges emerged, such as the failure of quarantine measures, further transmission by character’s pets and the existence of “immune” characters, who act as carriers, passing the virus to others while failing to succumb to symptoms.

Professor Fefferman said that the findings could be of great value to public health officials in developing the best way to manage the flow of information in such a crisis. “If, God forbid, a disease broke out in London, you could see what would happen if people were told immediately of the risk. Would there be panic and chaos, or would it allow them to psychologically accept the danger and act accordingly? What would happen if we made people feel too reassured?

“These are all things that have a great impact on the number of people who would be affected. They are also things we just don’t know, so [virtual games] could be of great value in helping us understand what their true emotional responses would be.”

World of Warcraft

— World of Warcraft is a “massive multiplayer online role-playing game” (MMORPG)

— There are about 6.5 million players worldwide. After the first free month, gamers have to pay

— Thousands of players adventure together, forming friendships, slaying monsters, and engaging in epic quests that can last weeks

— There are thousands of hours of game play, with a nearly infinite variety of goals to achieve and new content added regularly