A highly infectious strain of bird flu has been circulating worldwide since 2020
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H5N1 bird flu The virus has already spread all over the world better to infect people than previous tensions. Also, a single mutation could allow it to infect the cells lining our nose and throat, making it more likely to reach us in the air.
This change alone is not enough for the virus to be able to cause a pandemic. However, if a virus with this mutation swaps genes with a human flu virus, it could almost immediately become a potential pandemic.
“The more people infected, the more likely something like this is going to happen,” he says Ian Wilson at the Scripps Research Institute in California. However, Wilson believes the risk remains low.
A particularly virulent form of H5N1 bird flu developed in the 1990s, probably in domestic poultry in China, and spread worldwide. Around 2020, a new variant of this virus emerged and spread even further, to America and Antarctica. It has also infected a lot of domestic birds Spreading among U.S. dairy cows, causing occasional human cases.
The team led by him Debby Van Riel He has infected human nasal and throat cells with the 2005 and 2022 H5N1 variants at the Erasmus University Medical Center in the Netherlands. They have shown for the first time that the 2022 variant is better at binding to and even replicating within these cells. . “It’s bad news,” says van Riel.
“I don’t think the chances of the virus becoming a pandemic are very high,” he says. But making the virus better at infecting humans will give it more opportunities to acquire additional mutations that increase its pandemic potential.
In the meantime, Wilson and his colleagues have been studying the crucial flu virus hemagglutinin protein. This protein binds to receptors on the outside of cells, determining which cells the virus can infect. Since it is released from the virus, it is also a prime target of the immune system.
Currently, H5N1 hemagglutinin binds primarily to receptors deep in the lungs in humans. This means that it can cause serious illness but is unlikely to leave the body and infect others. To do this, the virus must infect the cells lining the nose and throat, meaning the virus can be coughed or sneezed out to infect others.
Van Riel’s research suggests that the virus can do this to some extent, but it is not clear whether the virus binds to the main receptors on these cells. It was thought that multiple mutations would be required for H5N1 to bind strongly to these receptors, but Wilson’s team has now shown that with the current H5N1 variant, it would only require a single mutation.
This change alone would not create a pandemic-capable virus, the team says Jim PaulsonAlso at Scripps Research Institute. “We see this property as necessary, but not important enough, for transmission, for a pandemic virus,” he says.
Other changes are also necessary for the virus to start replicating and spreading from person to person, Paulson says, and these are not well understood. “There’s a lot of biology we don’t know,” he says.
Once an H5N1 virus infecting humans acquired the receptor-shifting mutation, however, it would have the potential to develop these other changes as well.
Also, in theory, he can acquire all the abilities he needs in one fell swoop by exchanging genes with a human virus that infects the same individual. Various previous influenza pandemics caused animal and human influenza viruses to exchange genessays Paulson.
“This is very disturbing,” he says Aris Katzourakis at Oxford University, who was not involved in both studies. “Each spill on a human gives the virus a roll of the dice.”
How deadly would an H5N1 pandemic be?
If the H5N1 bird flu manages to start spreading from person to person, the big question is how deadly it would be. Of the people confirmed to be infected with the virus since 2003, half have died. However, the actual death rate from infections could be lower, as many cases have probably gone undetected, and softer ones will be lost.
Of the 60 people infected since the milk outbreak began in the US, almost all have had only mild symptoms. why it is not understoodbut one explanation is that many were infected through the eyes. “That’s known to have much smoother results,” says Katzourakis.
It is also thought that when viruses bind to receptors deep in the lungs and move to those higher up in the airways, they become less dangerous. But the puzzling aspects of the US cases have left Paulson unsure whether that will be true with H5N1. “I don’t know what to think now, to be honest,” he says.
“I don’t think there’s any reason to be complacent on that front, and to anticipate ‘softness’ if this virus is easily transmitted from human to human,” says Katzourakis.
Wilson’s team analyzed the hemagglutinin protein in isolation, so there was no possibility of laboratory spillover of the mutant protein. “No viruses were used here at all,” he says.
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