H5N1 has killed 60% of the 650 humans it's known to have infected in nearly two decades, making it an incredibly deadly but difficult to transmit virus. A new study tries to answer the question of how little it would take to make bird flu easily spreadable. The conclusion: 5 gene mutations. Controversial Dutch virologist Ron Fouchier in 2011 found the virus could go airborne—something health officials fear could mean an overwhelming pandemic—with nine or more mutations in ferrets, whose immune systems react to H5N1 much as our own do. He and his fellow researchers set out to find the minimum number of mutations needed to make that happen, the Los Angeles Times reports.
A ferret was infected with a genetically altered version of the virus and made to share air with another ferret—who eventually became sick. The researchers then uncovered the five mutations at play, two of which made the virus' ability to adhere to respiratory tract cells more robust. The other mutations bolstered the virus' stability and ability to replicate. Two big things to keep in mind: One, it's not known how likely these mutations are to occur outside a lab setting. "This certainly does not mean that H5N1 is now more likely to cause a pandemic," says Fouchier. Second, the altered virus wasn't as deadly as H5N1; Fouchier suggests this is because it hit upper, not lower, airway cells. But critics still say toying with H5N1 is dangerous. It could be some time before we see any benefit from the research, a microbiologist tells NPR, "and we have, meanwhile, just bought ourselves even more risk." (Read more bird flu stories.)