Dutch scientists have developed a mutant version of the deadly bird flu virus that could spread to humans.

The research team led by Ron Fouchier at Rotterdam's Erasmus Medical Centre had genetically altered a strain of the H5N1 bird flu virus that could spread for the first time among mammals. Flu researchers believe that if the pathogen were released it can trigger an influenza pandemic that would result in millions of deaths.

The H5N1 strain of bird flu is fatal is fatal in 60 percent of human cases but the threat of the virus has been mitigated because it spreads too inefficiently between humans. Since it emerged in 1997 there have only been 600 known cases of human flu. Now two unpublished studies from Fouchier at Rotterdam and Yoshihiro Kawaoka from the University of Wisconsin have worked out how to make the virus airborne without lessening its fatality rate.

Although Fouchier and Kawaoka worked independent of each other, they each hit on how to mutate the H5N1 virus to make it airborne. In Fouchier's case he passed the virus from one ferret to another multiple times. After 10 generations the virus had mutated to become airborne. Sick ferrets pass on the mutant strain by simply being housed in a cage next to healthy ferret. Ferrets have the same reactions to flu viruses as humans do and any influenza strain that has been able to pass among ferrets have also been shown to be transmissible among humans. A significant number of sick ferrets died showing that the airborne strain has the same lethality as the original H5N1.

Both studies are being reviewed by the National Science Advisory Board for Biosecurity which reviews papers that might benefit public health but could also be used dangerously. The NSABB will advise the researchers and journal editors how to publish the studies. However, some critics are adamant against publication saying that publishing the findings could be used by terrorists as a blueprint to creating bioweapons.

The EU Health Commissioner John Dali told the press that the virus was secure in Rotterdam.

"The Dutch authorities confirmed that the virus itself is stored in a very secured way and that the necessary permits were given and that the researchers are bound by a code of conduct," Dalli told the AFP. "One of the issues ... is to ensure that any information coming from this research is well controlled and without sensitive details about mutation being given," he said.