Bird flu virus experiments on how it could spread by respiratory droplets and trigger a pandemic have been published amid controversy over biosecurity and censorship concerns surrounding the research.

Scientists are watching how the H5N1 avian flu virus evolves closely both in nature and in laboratories because of its pandemic potential.

Dr. Ron A.M. Fouchier discussed how H5N1 becomes airborne in mammals. (Courtesy of Ron Fouchier/Science)

Thursday's online issue of the journal Science describes experiments that helped scientists to identify five changes in a strain of H5N1 that made the virus transmissible between ferrets through respiratory droplets.

Ferret animal models are considered the best way of testing how bird flu viruses infect humans and cause illness since the animals show similar symptoms to us.

The Dutch research was all conducted under strict biosecurity measures that were monitored by the Netherlands Erasmus Medical Centre, the U.S. National Institutes of Health and U.S. Centers for Disease Prevention and Control.

Healthy ferrets became infected with a bird flu virus that was mutated into what was thought to be a more mammalian form. The animals recovered.

Reassuringly, scientists could only find signs of a deadly virus when the virus was put directly into the ferrets' throats at extremely high doses.

Mutations already common

A second set of experiments in the U.K. suggested several circulating H5N1 avian influenza strains already have two of the mutations known to make experimental strains of the virus spread between mammals through respiratory droplets.

"Viruses that have two of these mutations are already common in birds, meaning that there are viruses that might have to acquire only three additional mutations in a human to become airborne transmissible. The next key question is, 'Is three a lot, or a little?'" study author Colin Russell of the University of Cambridge asked in a statement.

Russell's paper describes key factors that are thought to increase or decrease the likelihood of those mutations evolving.

"The eight-month controversy over how and whether to publish such studies has had the advantage of greatly raising public awareness concerning the real public health risk posed by the H5N1 avian influenza virus," wrote Science editor‐in‐chief Bruce Alberts.

"Scientists around the world will now have the ability to learn from this data and build on it to further advance our understanding of the flu virus, as required to prepare better defenses. And, we anticipate that, armed with new data, the scientific and public health communities will pursue all possible measures for averting a pandemic, including implementing improved surveillance strategies and developing new drugs and vaccines."