Virologists hold their breath for bird flu

In the US, bird flu is sweeping through dairy farms. Experts are wary of a scenario where the virus learns to spread among people. “We also have to monitor cows here so that we don’t miss anything.”

No, it is not certain that the next pandemic is imminent. But virologists are very alert to bird flu. They are looking with great concern at the US, where the H5N1 bird flu virus is spreading like wildfire among dairy cows. The first reports of dairy farms where bird flu had been detected came in mid-March. There are now more than a hundred of them, spread across twelve states. Three people who had contact with infected cattle fell ill. They suffered from an eye infection or a respiratory infection, but recovered. And, at least as important, they did not pass the virus on to other people. Because that is the worst-case scenario: that the virus changes in such a way that people pass it on to each other. No one can predict today whether that will happen, but no one can rule it out either.

Kristien Van Reeth, a professor of virology at Ghent University specializing in influenza viruses, says that an outbreak in cattle with the H5N1 bird flu virus is unprecedented and unexpected. “The virus has broken through a new barrier between animal species, which usually requires changes in the genetic code of the virus. It creates concern, because no one knows whether the virus will change further and then spread widely among other mammal species. This again requires many genetic changes and the chance of this happening is small. But it cannot be ruled out.”

According to Steven Van Gucht, virologist at the health institute Sciensano, it is not a good sign that the virus is spreading more and more in the US. “The more cows are infected, the more opportunity the virus has to infect people, for example during milking. And the more people get the virus, the greater the chance that it will adapt to humans. So everything must be done to get the outbreak in the US under control. I think that is still possible, but I see no signs of that at the moment.”

In the US, calls are now being made to prepare hospitals for patients with the H5N1 flu virus. “Although there is no evidence yet of human-to-human infections with the H5N1 virus, such a contamination could come to light at any time,” says an opinion piece in Statnews , which was signed, among others, by the Chief Biopreparedness Officer of the municipal health care system in New York City. Virologists also warned in The New York Times this week about the scenario in which the virus spreads among people. “If it gets into the general population, it’s too late,” said Erin Sorrell, a virologist at Johns Hopkins University.

“Then we have missed the boat.”

Testing cow’s milk

The H5N1 bird flu virus is not new. Since 2003, it has spread rapidly from Asia via migratory birds, first to Africa and Europe and eventually to America. “Over the years, the virus has undergone a major evolution,” says Van Reeth. “It is present in many bird species on all continents. Occasionally, infections have also been found in mammals, including minks and cats.”

In 2021, H5N1 bird flu reached America. The strain that is now circulating in cattle there is related to the H5N1 strain that caused major bird mortality in the years 2020 to 2023. “The virus has adapted further in America,” says Steven Van Gucht. “There has been an exchange of genes with other strains that are typically found there.”

The H5N1 bird flu virus has not yet been detected in cattle in Europe. But Van Gucht advocates monitoring via cow’s milk whether infections also appear in our country. In Germany, such studies have been launched in regions where bird flu is ravaging poultry. The virus can be found in unpasteurized cow’s milk. “We traditionally monitor bird flu via birds. But from Sciensano we propose to now extend this monitoring to cow’s milk. If we only have negative results, so much the better.”

Professor of biostatistics Niel Hens (UHasselt, UAntwerp), who coordinates a large European consortium that must prepare us for the next pandemic, fully agrees. “We have to keep an eye on how great the pressure from animals on humans is and how it evolves.”

The Federal Food Agency (FASFC) reports through its spokeswoman that the method for testing milk for bird flu is ready. But they do not plan to conduct analyzes with this “in the near future”. “Because there are currently no cases of bird flu in cattle in Europe and because the virus strain in America has never been detected in the EU.”

Seriously ill

What it would mean if H5N1 bird flu spreads to humans is anyone’s guess. The mild course of the three people infected in the US via cattle is somewhat reassuring. But H5N1 has a reputation for being very pathogenic. Since 2022, a number of infections of humans (mainly via birds) have been reported with the same virus strain. More than half of the patients with symptoms became seriously ill and there was also one death.

Nothing meaningful can now be said about the possible spread of the bird flu virus – how quickly it would occur. “That depends on many factors that we don’t know,” says Hens. “Such as the question of whether someone can pass on the virus before the first symptoms.”