Scientists have identified a mutation in the H5N1 “bird flu” virus that could enable it to infect and potentially transmit between humans. As the virus rapidly spreads among animals in the United States, researchers are on high alert for signs of human-to-human transmission. New studies indicate that the virus may only need one mutation to become transmissible among humans.
H5N1 is an extremely lethal virus, with a fatality rate of 50% in humans. Experts emphasize the importance of closely monitoring animal infections to prevent the virus from mutating further and jumping to humans, thereby averting a global outbreak.
While bird flu typically requires several mutations to pose a threat to humans, scientists at the Scripps Research Institute in California suggest that this time, the virus may evolve more rapidly, heightening concerns about a potential pandemic.
The findings, published in Science on December 5, 2024, underscore the need to track the virus’s evolution closely.
Currently, there are no confirmed cases of H5N1 transmitting between humans. Infections in people have been linked to close contact with contaminated environments or infected birds, poultry, cows, and other animals. However, health officials remain concerned about the possibility of the virus evolving to transmit efficiently between humans, which could spark a deadly new pandemic.
The flu virus attaches to its host through a protein called hemagglutinin, which binds to glycan receptors on the surface of host cells. Glycans are sugar molecule chains present on cell surface proteins and can serve as binding sites for certain viruses. Avian influenza viruses, such as H5N1, typically infect hosts with sialic acid-containing glycan receptors found in birds (avian-type receptors). Although these viruses rarely adapt to humans, if they evolve to recognize sialylated glycan receptors present in humans (human-type receptors), they could potentially gain the ability to infect and spread between people.
“Monitoring changes in receptor specificity—the way a virus identifies host cells—is crucial because receptor binding is a key step toward transmissibility,” explains Ian Wilson, DPhil, co-senior author and the Hansen Professor of Structural Biology at Scripps Research. “However, receptor mutations alone don’t guarantee that the virus will transmit between humans.”
“The findings show how easily the virus could evolve to recognize human-type receptors,” adds first author Ting-Hui Lin, a postdoctoral associate at Scripps Research. “However, our study does not suggest that this evolution has occurred, nor does it imply that the current H5N1 virus with only this mutation would be transmissible between humans.”
