Start mass testing dairy workers for bird flu
Given how devastating another global pandemic would be, the US should start mass testing of dairy workers for the bird flu virus that’s spreading fast through cows. If necessary, either the Centers for Disease Control and Prevention or the US Department of Agriculture should pay people to get tested. The USDA’s recent call to test more cows isn’t going far enough.
This week, scientists announced they’d found viral fragments in milk on supermarket shelves, with an alarming 58 of 150 samples testing positive. Scientists initially thought that milk from infected cows was always thick and discoloured, but these results show it can look deceptively normal.
These fragments are unlikely to infect consumers because the pasteurization process heats milk enough to destroy the live virus. But the prevalence of viral fragments shows this disease is much more widespread than thought in cows, said Andrew Bowman, an expert in animal influenzas at The Ohio State University and leader of this latest milk testing effort. And it’s spreading stealthily, with many of the infected cows not visibly sick.
Could the same silent spread be happening in people — starting with dairy workers and putting us all at risk of a new pandemic? It’s possible, and while this probably hasn’t happened yet, every jump to a human gives the virus a new chance to stumble on the combination of mutations that give it pandemic potential. And this won’t be the last animal virus to threaten us.
Farm workers represent a critical conduit through which animal viruses can get i nto humans, but monitoring them falls through the cracks, said biologist Laura Kahn, a physician who had studied biological threats at Princeton University before co-founding the One Health Initiative aimed at pandemic prevention.
The USDA focuses on animals, while the National Institute for Occupational Safety and Health does other kinds of occupational studies. Occupational exposures haven’t been in the province of the CDC, she said. “There’s a gap in the federal government in who is monitoring the workers.”
On Tuesday, the USDA announced it is finally requiring that dairy cows be tested for this virus before being moved to other farms. That should have happened weeks ago since the virus is already in at least 33 farms across multiple states. Milking equipment that was used on infected cattle should be destroyed, said Dr Kahn, and the animals quarantined. Raw milk represents another risk, she said.
Assoc Prof Bowman told me that any given carton of milk can be made up of milk pooled from different sources. Just because a third of milk samples show signs of the virus doesn’t necessarily mean a third of US dairy cattle are infected. But because the milk they tested came from diverse parts of the country, it shows that the disease is surprisingly widespread. “There are definitely animals that don’t show any clinical signs of disease,” he said. He said researchers still don’t know how it got into cattle or how it’s spreading from one animal to another.
At the beginning of April, officials announced the first human case linked to these dairy outbreaks. Dairy workers are routinely exposed to milk that sprays or is aerosolised, and there could be many more infected people who haven’t been tested.
This kind of flu virus, called H5N1, was first discovered among domestic birds in China in the 1990s. After dying down, it re-emerged in 2003, spreading to Europe, Africa and the Middle East and acquiring a variety of new mutations.
In 2021, a new, fast-spreading version exploded across wild and domestic birds around the world, killing millions of chickens and turkeys, including more than 50 million in the US in 2022. Crowded conditions helped fuel its spread, and many chickens are bred to be genetically identical, making them vulnerable to infectious diseases.
This new version of the virus has also been versatile, infecting and killing foxes, seals, bears, dolphins, porpoises and other mammals. In 2023, it broke out in a mink farm in Spain, and good surveillance led to testing of the workers and containment of the threat.
“The scope and breadth and flavour of different mammals infected with this virus are quite remarkable,” said Richard Webby, a specialist in influenza at St Jude’s Children’s Research Hospital in Memphis. Before the 1990s, H5N1 had a natural host in wild waterfowl, but this new version has been causing large die-offs, especially in wild birds and sea mammals, Dr Webby said. “It’s quite horrifying.” He’s particularly worried the virus will find its way into pigs. They’re known to incubate new flu variants that can be suited to infecting humans.
Although humans have been sporadically picking up this bird flu virus over the last 20 years, and some have died, it has yet to mutate into something that spreads easily from person to person. But if that happens, it could become widespread before it causes enough severe disease to be noticed — just as Covid-19 did.
Testing people where they’re most likely to get infected could help us keep it contained. And every day counts.