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What would it take for the bird flu virus infecting cattle to start spreading between humans and causing a pandemic? A study published today in the journal Science offers some new and concerning clues. NPR's Will Stone reports.
WILL STONE, BYLINE: A bird flu infection starts when a protein on the virus binds to a receptor on the cell it wants to take over. Luckily, the version of H5N1 spreading in cattle has not evolved to target the receptors that dominate upper airways in humans. For that to change, there would need to be mutations affecting the viral protein so that if someone were infected, the virus could easily spread.
JIM PAULSON: When you sneeze on someone, you have a very small amount of virus that's being transferred through the air.
STONE: That's Jim Paulson at Scripps Research Institute.
PAULSON: In that context, it becomes extremely important for the virus to have success - to be able to latch on strongly to the receptors that it encounters.
STONE: For many years, Paulson and his collaborator, Ian Wilson, also at Scripps, have tracked how other dangerous influenza viruses have made this leap. They wanted to know - could this happen with the latest bird flu virus?
IAN WILSON: We looked at these mutations one at a time.
STONE: This was in the lab using proteins, not actual viruses. They did a handful of experiments. Most mutations did not lead the viral proteins to switch from an avian-type receptor to a human-type, but there was one.
WILSON: It was completely switched.
STONE: Wilson says all it took was one mutation in the right spot. They were expecting from previous research it might take three.
WILSON: That was really quite surprising.
STONE: And concerning because it raises the odds of this happening. Paulson says one mutation was enough in some previous influenza pandemics to allow the virus to switch to human-type receptors, triggering some of the early infections. That said, he's quick to point out...
PAULSON: ...We don't want to lead with the - that we think that this is going to happen tomorrow.
ANICE LOWEN: I think it's significant, but it shouldn't cause alarm.
STONE: Anice Lowen is a virologist at Emory University who wasn't involved in this new research.
LOWEN: There's other requirements - other changes a virus would need to go through to efficiently transmit in humans and cause a pandemic.
STONE: Some of these we know about, others we may not. And, Lowen says, with so many cattle carrying the virus, she worries there will be more cases in people.
LOWEN: There's just a lot of potential human exposure there, and so that's where the great risk lies.
STONE: Because every spillover into a person gives the virus more chances to pick up this mutation.
Will Stone, NPR News.
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