ChinaFotoPress/Getty Images

All it would take is five gene mutations of the H5N1 avian influenza virus to potentially create havoc on a global scale. Dutch researchers are reporting that if those mutations happen, the virus would become transmissible via coughing or sneezing, just like regular flu viruses. Currently, most cases of H5N1 arise after a person has had contact with sick or dead infected poultry.

To give an idea of how deadly the avian flu virus is, scientists at one point stopped conducting research on H5N1 over concerns that in the wrong hands it could be used as a biological weapon by terrorists. Of the 650 people infected since H5N1 was first identified in Hong Kong 17 years ago, 60 percent died because of the disease.

Health officials have feared that H5N1 would evolve, but they are not sure if the virus is likely to mutate outside of a laboratory. "The biggest unknown is whether the viruses are likely to gain the critical mutations naturally," says Richard Webby, a virologist at St. Jude Children's Research Hospital in Memphis. "If they can appear readily, then it is very worrisome. If not, then there's still a major hurdle that these viruses have to get over to become human-transmissible."

During the study, which was published Thursday in the journal Cell, researchers used ferrets as stand-ins for humans. They sprayed an altered version of the H5N1 virus into a ferret's nose, then put it in a special cage with a ferret who had not been exposed. The cage was constructed to allow shared airflow without direct contact, and when the healthy ferret exhibited signs of the flu (loss of appetite and energy, ruffled fur) they knew the virus had spread through the air. Read more about the study and its findings at the Los Angeles Times.