Two papers published this week, and one last month, reveal the pandemic potential of
H5N1 “bird flu”. One identifies four, another identifies five, genetic changes the virus would have to undergo before it could spread easily in humans, and the third paper suggests some of these changes are already evident in circulating strains.
The papers were written last year, but were held back because of international concerns that making such data public would make it easier for terrorists to make bioweapons.
H5N1 Currently Not Pandemic in Humans
H5N1, or “bird flu“, is a subtype of the influenza A virus that can cause illness in humans and many other animals. It has killed tens of millions of birds and spurred the culling of hundreds of millions of others to stop it spreading.
Since 2003, more than half of the 606 cases of human infection of H5N1 reported to the World Health Organization worldwide, have resulted in death. Most of the cases in humans appear to have occurred as a result of contact with infected birds.
So far, H5N1 has not triggered a pandemic in humans because it does not spread easily among mammals, and some scientists believe it never will. To spread easily from one person to another, the virus would have to become airborne, that is develop the ability to spread via tiny droplets that people spray out of their mouths and noses when they cough and sneeze. That is how other flu viruses, like the H1N1, the “swine flu“, that caused a mild pandemic in 2009, spread.
Viruses like H5N1 and H1N1 are mutating all the time. If H5N1 were by chance to acquire some of the properties of H1N1 then it would spread more easily in mammals. One way it could do this is by accumulating chance mutations, another way is by swapping genes with other viruses, for instance while co-infecting an intermediate host (genetic “reassortment”).
Much of the focus of H5N1 research, amid concerns about the bioterrorism risk, has been to investigate how easy it might be for H5N1 to mutate into a readily transmissible form, and if so, which genes would be involved. This information is useful for surveillance, so researchers know what changes to look out for in emerging strains when assessing pandemic risk.