Last Friday, the inspectors of the American Food and Drug Administration (FDA) may have become restless. For weeks they had traveled across the country, visiting supermarket after supermarket – to buy milk and have it analyzed in their laboratories. What they found is also causing concern among experts: one in five samples contained components of the bird flu virus A/H5N1.
The alert has been increasing in the United States for several weeks. In March there were the first indications that the notorious pathogen A/H5N1 was spreading in domestic cattle herds. The World Health Organization’s situation report at the time referred to “isolated cases”.
But 34 herds in at least ten states are now affected. Since then, states have intervened in the cattle trade. At least 22 have imposed transport restrictions on dairy cows. No cattle are allowed to be imported there without a permit. As of Monday, April 29, 2024, any animal transported between states must be tested for bird flu beforehand.
There is great concern among US surveillance authorities. This is the virus that is currently rampant across the globe and is killing wild birds and farmed poultry by the millions. In summer it was raging on the coasts of the North and Baltic Seas. The Norwegian authorities counted 13,000 dead seagulls last August alone.
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Environmentalists have feared for penguin colonies in Antarctica since the virus was brought to the southernmost continent by skuas in February 2023. And in Germany last year alone, hundreds of thousands of chickens, geese, ducks and turkeys had to be slaughtered because the animals were infected by infected migratory birds.
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But mammals have also been falling ill for a long time – and every transmission harbors the possibility that the virus will adapt to humans. Spain experienced its first major outbreak in 2022, when bird flu suddenly spread among martens on a mink farm. More than 50,000 animals had to be slaughtered.
From then on, things happened quickly: scientists found the virus in foxes, bears and squirrels. They noticed with some horror that about a year ago, thousands of sea lions and young southern elephant seals died along the South American coasts.
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Time and again, people became infected from their infected livestock; in the USA, a farm employee has now fallen ill with bird flu. Most of the time the infections were mild. And these are still isolated cases. But if the virus gains the ability to jump from one person to the next, the next pandemic would be inevitable.
The situation in the USA worries experts primarily because cattle have not previously been considered hosts of the bird flu virus – and they live in close contact with humans. They are fed, mucked out, milked. And so the risk that more people will become infected and that the virus will continue to adapt increases.
It is not yet clear how wild birds could have transmitted the virus to the cows. But scientists have analyzed the genome of the virus – according to the Science Media Center, everything that is happening in the USA can be traced back to a single entry. This cow may have contaminated the milking machines and/or gloves of the farm employees via an inflamed udder.
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This assumption is supported by the observation that the pathogen multiplies rapidly, especially in the udders of infected cattle – unlike in the respiratory tract, where it could only be detected in small quantities. In their genetic analysis, researchers also found only a few mutations.
“The actually astonishing thing is: Apparently the H5N1 virus does not need many adaptations in order to be able to reproduce in dairy cows,” says Martin Schwemmle, research group leader at the Institute of Virology at the University Hospital of Freiburg, the Science Media Center. This may sound like a relief to many because it makes respiratory transmission less likely.
But the high viral load in the udders causes other problems. “This means that the virus is not only spread with every drop of milk that enters the environment, but that the entire equipment necessary for milk production can be contaminated with infectious virus,” says Schwemmle. It is very difficult to get such widespread contamination under control.
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According to the FDA, the milk sold in supermarkets poses no danger. The virus is killed by ultra-high heat, which is used to preserve milk. The remaining fragments are unable to cause an infection.
And the high number of positive detections would not mean that every fifth pack is affected – the particles could also be traced back to individual farms and a few cows, as the cows excrete so much virus. However, doctors and health authorities warn against consuming untreated milk, so-called raw milk.
“If I were in charge, I would ban the sale of raw milk at the moment,” said Thijs Kuiken, pathologist in the department of virology at the Erasmus Medical Center in Rotterdam, to the industry service “statnews”. Kuiken has been researching H5N1 and the damage it causes for about two decades. He doesn’t fear so much the possibility that the virus could mutate and trigger a pandemic.
But he believes people who drink raw milk from an H5N1-infected cow would likely become seriously ill. In studies, he experimentally infected animals with H5N1 to record the disease the virus causes. But the current reports about the amounts of virus in infected udders are higher than anything he has examined himself.