“A mutation occurs in the avian flu virus that makes it easy to spread to humans.”

After testing the virus in the body of a Canadian teenager hospitalized with avian flu, it was discovered that mutations occurred in key areas that made it easier to spread to humans. This is what CNN reported on the 21st (local time) based on the analysis of American scientists who examined this virus.

Fortunately, it has been confirmed that no one other than this teenager has been infected so far. British Columbia’s provincial health officer, Dr. Bonnie Henry, said after monitoring dozens of potential contacts among the teen’s friends, family and health-care providers, “no additional cases were identified.” This means that the mutant virus does not spread or pose a threat to other people.

The H5N1 avian flu virus that infected this teenager, who is in critical but stable condition, is not the same mutation as the avian flu virus prevalent in dairy cattle in the United States. It is more closely related to the H5N1 variant prevalent in wild birds such as geese in the Pacific Northwest. Both mutations are H5N1, but there are genetic differences, as Delta and Omicron were different versions of the COVID-19 virus (SARS-CoV-2) that causes COVID-19.

Disease investigators investigating the case do not yet know how the teen became infected because he had no known contact with wild birds. “This is certainly the first time we have seen evidence of this type of adaptive mutation in H5,” said Dr. Jesse Bloom, a computer virologist at the Fred Hutchinson Cancer Center in the US who tested the virus extracted from the teenager.

Dr. Bloom and other scientists discovered three mutations at locations in the virus genome that they determined made it easier to attach to human cells. The flu virus penetrates by attaching to a sugar that protrudes from the cell surface, called sialic acid. Birds are rich in alpha-2 and alpha-3 sialic acids, while humans have alpha-2 and alpha-6 sialic acids, mainly in the nose, throat, and lungs.

Scott Hensley, a professor of microbiology and immunology at the University of Pennsylvania who specializes in flu virus research, explained that it has been possible to know what mutations of interest are through decades of basic research. On the 16th, he analyzed the base sequence of a Canadian adolescent patient posted to the International Organization for Sharing Influenza Information (GISAID) and found that the virus preferred alpha 2 and alpha 3 receptors, which are abundant in birds, but preferred alpha 2 and alpha 3 receptors, which are abundant in the nose, throat, and lungs of humans. It was revealed that the change that can be converted to alpha-6 sialic acid was accurately confirmed.

He pointed out that one of the places in the human body with many alpha 2 and alpha 3 receptors is the eyes. Most human H5N1 infections reported in the United States have red and inflamed eyes as the initial symptom, suggesting the virus has entered the body.

One of the Canadian teenagers’ first symptoms was bloodshot eyes. Professor Hensley pointed out that this suggests that the virus may have entered through the eyes. Additionally, the Canadian teen developed a serious breathing disorder called acute respiratory distress syndrome (ARDS). He explained that this could be the result of mutations that the virus began to acquire as it mimicked itself in the body.

Dr. Bloom explained that this can happen when a virus evolves in a host and exists in various forms in the body. “When looking at sequence analysis of how the virus is evolving within a single host, it is generally observed that symptoms disappear for several weeks after infection and then various mutations become mixed,” he said.

The Canadian teen began showing symptoms a week before being admitted to the hospital. This may have been the time the virus needed to better infect the cells it was trying to infiltrate.

Dr. Bloom noted that this specific mutation was not found in the H5N1 viruses found in infected birds in Canada and the United States. In that sense, the mutation in question may be a mutation that must be passed in order to survive in the human host. In other words, even if the Canadian teenager’s infection was an external infection without additional infection, the same mutation may occur again if infection occurs again in another person.

In the United States, 53 cases of bird flu have been confirmed in humans. Infections occur consistently in dairy cattle, sporadically in poultry, and widely in wild birds. “The H5N1 flu virus is circulating a lot out there,” said Dr. Bloom. “Flu viruses have a high mutation rate, so if this virus is in an evolutionary space suitable for acquiring mutations once, it may acquire mutations again in another infection, although it is not certain. “You can,” he said.