WASHINGTON - Scientists say the H5N1 avian influenza virus has the potential to infect and spread among humans, raising the possibility of a catastrophic global pandemic. This and other findings about H5N1 were published this week in the journal Science, less than a year after their release was withheld at the request of US government and World Health Organization officials, over concerns that the information could fall into the hands of terrorists.
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In a series of articles published in Science, researchers describe how the H5N1 avian flu virus is capable of jumping species and being spread by airborne transmission among mammals -- including humans.
Dutch and British researchers conducted experiments with ferrets, small mammals that provide a good model for human illness. The scientists found they could infect the upper airways of the animals with a mutated H5N1 virus. Scientists say none of the ferrets died.
Guided by genetic studies of the viruses that caused the virulent flu pandemics of 1918, 1957 and 1968, investigators identified the genetic changes that would be necessary for a global outbreak of H5N1. Investigators concluded that as few as five gene mutations enabled the bird flu virus to jump the species barrier and become infectious among mammals.
Derrick Smith is with the University of Cambridge England and the Fogarty International Center at the National Institutes of Health near Washington.
Smith used a mathematical model to determine whether the existing virus could naturally acquire the mutations needed to become a human pandemic threat. In a telebriefing with reporters, Smith said researchers now know that it could.
"This is a little like being in a situation where as we would all like to, for example, predict an earthquake or a tsunami. We now know that we're living on a fault line," he said.
But according to Smith, it's hard to predict if or when H5N1 could strike, developing the remaining mutations or genetic substitutions in birds that would make the avian virus transmissable to humans.
"I mean it's a bit like saying, 'could it ever snow in the Sahara?' I mean, could it ever happen? I mean, what we show is that (with) these remaining substitutions, it is absolutely within the realm of possibility that they evolve in a human host or some other mammalian host. We see no fundamental hurdle to that happening," Smith said.
Researchers say more experimental research is needed to predict the transmissibility of the avian virus.
Another manuscript just published in Science lays out strategies to prepare for a bird flu pandemic, including vaccinating as many people ahead of time with existing H5N1 vaccines to prime their immune systems and lessen the severity of a pandemic. Research is underway to make large quantities of a vaccine specifically against the deadly flu strain.
Ron Fouchier is a virologist at Erasmus University in the Netherlands who co-authored the paper on the transmission of H5N1.
Commenting on the researchers' decision last year to honor the government request not to publish their findings until now, Foucher says would-be terrorists could have gotten information any time on other pathogens that are more deadly and more easily transmissable than the bird flu virus.
"So anybody with access to the scientific literature can read all about dangerous pathogens that are more interesting to terrorize the world with than our particular virus," Foucher said.
A separate paper was published in May in the journal Nature by Japanese researchers identifying other genetic mutations that could lead H5N1 to jump the species barrier and become a threat to humans.