New Mutations Identified in Bird Flu Virus

The avian flu virus sweeping through dairy farms in several states has acquired dozens of new mutations, some of which could make it better able to spread between species and less susceptible to antiviral drugs, a new study suggests.

None of the mutations are alarming in themselves. But they highlight the possibility that as the outbreak continues, the virus will evolve in ways that allow it to spread easily between people, experts say.

“The flu mutates all the time — that’s kind of what the flu does,” said Richard Webby, an influenza expert at St. Jude Children’s Research Hospital, who was not involved in the work. .

“The real key would be if we start to see some of these mutations become more prevalent,” Dr. Webby said. “That would increase the level of risk.”

The virus, called H5N1, has infected cows in at least 36 herds in nine states, raising fears that the milk is infectious – concerns now largely dispelled – and highlighting the risk that many viruses can spread from species to species. the other in overcrowded farms.

The study was posted online Wednesday and has not been peer-reviewed. He is one of the first to provide details of an Agriculture Department investigation that has so far remained mostly opaque, frustrating experts outside the government.

The outbreak most likely began about four months before it was confirmed in late March and spread undetected through cows that showed no visible symptoms, the researchers found. This timing is consistent with estimates from genetic analyzes carried out by other scientists.

The virus has been detected in some dairy herds with no known links to affected farms, the authors said, supporting the idea of ​​transmission from cows without symptoms and suggesting there may be infected herds that do not. have not yet been identified.

The widespread nature of the outbreak also suggests effective spread among cows, according to the new paper. This can pose significant risks to people who interact closely with these animals.

“The fact that this has been transmitted to cows for some time is really concerning,” said Louise Moncla, an evolutionary biologist who studies avian flu at the University of Pennsylvania and was not involved in the work.

“I’m very concerned about being able to be sure that we find cases in humans,” she said.

In the new study, researchers collected samples containing the virus from 26 dairy farms in eight states. Cows are not generally susceptible to this type of flu, but H5N1 appears to have acquired mutations in late 2023 that allowed it to jump from wild birds to cattle in the Texas panhandle, researchers said.

The virus then appears to have spread to dairy farms from Texas to Kansas, Michigan and New Mexico. Since then, in at least a dozen cases, H5N1 has also spread from cows to wild birds, as well as poultry, domestic cats and a raccoon.

The findings should prompt widespread surveillance not only of affected farms, but also those without reported infections, said Dr. Diego Diel, a virologist at Cornell and author of the study.

Many other species were likely infected after coming into contact with contaminated milk, which can contain very high levels of virus, Dr. Diel said. A separate study published earlier this week reported that about a dozen cats fed raw milk died.

It is not uncommon for dairies to dump waste milk into manure pits or lagoons. This “could certainly serve as a source of infection for other susceptible species,” he said.

Researchers are closely monitoring H5N1 genetic sequences from cows for mutations that would allow the virus to more easily infect or spread among mammals, including humans.

The only person to be diagnosed with bird flu during the current outbreak carried a virus with a mutation that allowed it to infect people more effectively. One cow in the study also carried H5N1 with this mutation. More than 200 other people have been infected with versions of the virus carrying a different mutation providing the same benefit.

Veterinarians began observing unexplained drops in milk production in cows in late January and sent samples for analysis. The Ministry of Agriculture only confirmed the infections on March 25.

“The more H5N1 spreads, the more likely it is that it will encounter a combination of mutations that could increase its risk to humans,” said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Center in Seattle.

“On the other hand, H5N1 has been circulating in various species and causing sporadic human infections for more than two decades, and so far we have not had a pandemic,” he said. “It’s one of those situations where it could happen next week, but it also could never happen.”