Bird flu appears to be slowly mutating to better infect humans. Experts warn now is the time to act

In late March, a worker at a commercial dairy farm in Texas came down with pink eye. He eventually tested positive for the highly pathogenic avian influenza type A H5N1, also known as bird flu. Scientists were shocked to discover that cattle, not birds, were the host — and that high levels of H5N1 were found in the infected cattle.

So far this year, there have been four confirmed human cases after exposure to a dairy cow, with at least 143 dairy herds affected in a dozen states. For years, scientists have warned that bird flu could become another pandemic like COVID-19 (which isn’t quite over yet). In other species, scientists have watched H5N1 decimate populations of seals and cats. Now, a new study published in the journal Nature takes a closer look at the virus that infects cows, and sheds light on the risk it poses to human populations.

The study found that the H5N1 virus spread to the mammary glands of mice and some ferrets after the virus was isolated from an infected cow.

“There’s good news and bad news,” study co-author Keith Poulson, director of the Wisconsin Veterinary Diagnostic Laboratory, told Salon. The good news is that scientists have a model for infecting lab animals and having them shed the virus in their mammary glands. In the study, scientists specifically found that when mice and ferrets were infected with the virus, it spread to the brain, intestines, kidneys, heart and lungs. It also spread to the mammary glands of mice and some ferrets. While transmission didn’t occur through direct contact between mice, the female mice did pass it to their young through their milk.

Typically, influenza viruses—like the kind that spikes every winter but is considerably more benign than bird flu—spread among mammals via airborne droplets when an infected person coughs, sneezes or talks. This is known as respiratory transmission. The study’s findings suggest that the current strain isn’t great at respiratory transmission. On the surface, that’s good news. But the final part of the study has scientists concerned.

“The bad news is that this is going to attach to both sets of sialic acid receptors,” Poulson told Salon. These receptors are widespread in the upper respiratory tract of humans. In birds, H5N1 strains typically target different sialic acid receptors. But now it has clearly adapted to mammalian receptors, which could give the virus greater capacity for transmission between humans.

One of the main reasons H5N1 hasn’t become a pandemic yet — emphasis on yet — is that it’s pretty bad at spreading from person to person. If it ever develops that ability, a distinct possibility, it could easily sweep through a population and create a textbook pandemic. In fact, that’s exactly what SARS-CoV-2, a virus that first appeared in bats, did in 2019.

“So we really need to pay attention to this virus; we cannot allow it to remain endemic in our dairy herds,” Poulson said.

“We really need to pay attention to this virus.”

In the final part of the study, scientists found that unlike older strains of H5N1, this one has the capacity for ‘double binding’, suggesting it could be possible for people to become infected in their respiratory tract. However, the scientists said they need more information.

Poulson said that in light of the findings, he welcomes the announcement last week by Human Services of a contract with vaccine developer Moderna to produce an mRNA vaccine targeting bird flu. “We have successfully taken lessons learned during the COVID-19 pandemic and used them to better prepare for future public health crises,” HHS Secretary Xavier Becerra said in a statement. “As part of that, we continue to develop new vaccines and other tools to address influenza and strengthen our pandemic response capabilities.”

“We don’t want to be behind the curve like we were with COVID,” Poulson said. “It’s worth preparing for, so if this were to change, even if it’s a very small chance, if it were to change, we’re ready.”


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Professor Ian Brown of the Pirbright Institute, who leads a research consortium investigating similar questions about receptor binding, said in a press statement that the “predicted binding to cells provides new evidence for broader adhesion, including to cells lining the upper airways of humans, but more research is needed to understand the underlying factors.”

“Overall, the study’s findings are not unexpected, but this report provides further scientific insight into an evolving situation,” he said. “That highlights the need for strong monitoring and surveillance of affected or exposed populations, both animals and humans, to identify future risks.”

Dr. Rajendram Rajnarayanan, of the New York Institute of Technology’s Jonesboro, Arkansas, campus, told Salon that he is concerned about the latest study’s findings, but that the concerns are not yet “alarming.”

“There are things that we expect to happen if we don’t get the spread under control,” Rajnarayanan said. “There’s a possibility that if it binds now, it will try to bind better. It’s always going to mutate, and that’s a major concern.”

According to Rajnarayanan, genomic surveillance is crucial to achieve efficient human-to-human transmission through the respiratory tract.

“Typically, the potential for anything that infects the upper respiratory tract to spread from person to person is quite high,” Rajnarayanan said. “So far, we haven’t seen that, but what we have seen is that this can bind to both receptors. That’s the information we have now.”

How efficiently they bind is what scientists now need to look at. “Once it’s transmitted from person to person, it’s going to spread like we’ve seen with other viruses that can cause a pandemic,” he said.

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