The H5N1 virus, also known as bird flu, has now spread around the world and is more capable of infecting humans than previous strains. Just one genetic mutation could allow the virus to infect cells in the nose and throat, increasing the likelihood of airborne transmission.
However, mutation alone is not sufficient to initiate the world. If the virus swaps genes with the human virus, it could quickly become a global threat. Ian Wilson “The more people that are infected, the more likely that change is going to happen,” he told New Scientist at the Scripps Research Institute in California. But he emphasizes that the risk of such a scenario is still low.
The H5N1 avian influenza virus first emerged in the 1990s, probably among domestic birds in China, and spread worldwide. In 2020, a new strain of the virus emerged and was able to spread more widely, even reaching the American and Antarctic continents. In addition to domestic birds, the new strain has also infected dairy cattle in the United States and has sometimes been transmitted to humans.
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A group of researchers under the supervision Debbie Fanrail from Erasmus University in the Netherlands, infected human nasal and throat cells with H5N1 strains from 2005 and 2022. The results showed that the 2022 strain not only has a greater ability to bind to cells, but also works more effectively in proliferation. Fanrail describes this finding as “bad news”, although he believes the probability of the virus spreading to the world is still low. “As the virus gets better at infecting humans, it provides more opportunity for dangerous mutations to occur,” he says.
On the other hand, Wilson’s group is also studying the hemagglutinin protein of the virus. This protein determines what type of cells the virus attaches to, and since it protrudes from the surface of the virus, it is also the main target of the immune system.
The virus causes severe illness, but the chance of transmission is low
Currently, the hemagglutinin of the H5N1 virus binds mostly to receptors deep in the lungs. This feature makes the virus cause severe disease, but reduces the chance of transmission to others. In order for the virus to be easily transmitted, it must infect cells in the nose and throat, as this allows transmission through coughing and sneezing.
The study by the Fanriel group shows that the virus has partially achieved the ability it needs. However, it is not yet known whether it binds to the main receptors of the cells. It was previously thought that the virus needed multiple mutations to do this. But Wilson’s group has shown that just one mutation is enough to create such a capability.
however, Jim Paulson From the Scripps Institute, one of the researchers in Wilson’s group warns that the mutation alone is not enough to cause the world. “This property is necessary for virus transmission, but it is not sufficient by itself,” he says. He adds that other changes are necessary for the virus to be transmitted between humans, but these changes are not yet fully understood.
Also, Paulson explains, if the H5N1 virus acquires the receptor-binding mutation to be able to infect humans, it may gradually find the other changes it needs. In addition, if a person is infected with the human virus and the H5N1 virus at the same time, the possibility of genetic exchange between the viruses also arises. Such a process can transfer to the virus all the features necessary for the world in one moment. According to him, some cases of influenza in the past started with this method.
Iris Katzourakis from the University of Oxford describes the current situation as “extremely worrying” and says: “Every time the virus spreads to humans, it can have dangerous consequences, like the roll of the dice.”
How deadly will the spread of the H5N1 virus be?
If the H5N1 virus is transmitted from human to human, the important question is how deadly it will be. Since 2003, half of the people infected with this virus have died. However, the actual death rate may be lower, as many mild cases are likely to be undiagnosed.
Half of the people infected with the H5N1 virus have died
In the United States, of the 60 or so people who have been infected since the H5N1 virus broke out among cattle, nearly all have had mild symptoms. The reason for this is not clear, but many may have been infected through the eye, and this route usually results in milder symptoms. “It’s clear that the virus has much milder symptoms,” says Katzourakis.
It seems that if viruses bind to receptors in the upper respiratory tract instead of deep in the lung, the severity of the disease is also reduced. However, Paulson is skeptical about the hypothesis, saying, “To be honest, I’m not sure what to think.”
But Katzourakis cautions, “There is no reason to be complacent. It should not be expected that the virus will be mild if transmitted from person to person.
Wilson also emphasizes that his group only studied the hemagglutinin protein in a safe environment and no virus was used in this research. “There was no risk of lab leaks in our lab,” he says.
The findings of Fanrail’s group have been published in the Bioarchive database and the study of Wilson’s group has been published in Science magazine.
