U.S. health and agriculture officials are increasing testing and tracking of bird flu in dairy cows in an urgent effort to understand and stop the growing epidemic.
Officials have said the risk to humans remains low so far, but scientists are cautious that the virus could change to spread more easily between people.
The virus, known as Type A H5N1, has been detected in nearly three dozen dairy herds in eight states. Inactive viral residues have been found in grocery store milk. Tests also show the virus is spreading among cows, including those showing no symptoms, and between cows and birds, according to the U.S. Department of Agriculture.
Starting Monday, hundreds of thousands of lactating dairy cows in the U.S. will need to be tested with negative results before being transported between states under the new federal order.
Here’s what you need to know about the ongoing bird flu investigation:
WHY IS THIS PANDEMIC SO EXTRAORDINARY?
This strain, known as highly pathogenic avian influenza, has been circulating in wild birds for decades. In recent years, it has been detected in many mammals worldwide. Most were wild animals such as foxes and bears that ate sick or dying birds. But it has also been seen in farmed minks. It is also seen in aquatic mammals such as harbor seals and porpoises. The virus was even found in a polar bear in northern Alaska.
The virus was discovered in ruminant animals (goats and then dairy cows) in the United States this spring, surprising many scientists who have been studying the issue for years.
St. “When we think about influenza A, cows aren’t usually in the conversation,” said Richard Webby, an influenza expert at St. Jude Children’s Research Hospital.
Flu viruses are notorious for adapting to spread among new strains, so their detection in dairy cows raises concerns they could spread to humans, Webby said.
HOW LONG DOES BIRD FLU SPREAD IN COWS?
Scientists confirmed the virus in cows in March, following weeks of reports from dairy farms of animals falling ill. Symptoms included lethargy, a sharply reduced milk supply, and changes such as the milk becoming darker and yellower.
Matthew Aliota, a veterinary researcher at the University of Minnesota, said the discovery of traces of the virus in commercial milk “shows that this has been around for longer and is more widespread than we previously realized.”
Under pressure from scientists, USDA officials this week released new genetic data on the outbreak.
Michael Worobey, an evolutionary biologist at the University of Arizona, said the data did not include some information about when and where the samples were collected, but it did indicate that the virus likely spread from birds to cattle late last year.
The disease has since spread among cattle and between farms, Worobey said, possibly through contact with physical objects such as workers’ shoes, trucks or milking machines.
The cows then spread the virus back to the birds, he said.
“The genetic evidence is as clear as it gets,” Worobey said. “The birds sampled on these farms contain viruses with distinct mammalian adaptations.”
WHAT ARE SCIENTISTS SAYING ABOUT EFFORTS TO TRACK THE OUTBREAK?
Many experts said the USDA’s plans to require testing in cows are a good start.
“We need to be able to do more surveillance so we know what’s going on,” said Thomas Friedrich, a professor of virology at the University of Wisconsin veterinary school.
Worobey said the ideal would be to scan every herd. In addition to looking for active infections, agricultural officials should also look to see if cows have antibodies to the virus, which indicates past infections, he said.
“This is a really accessible and quick way to find out how common this is,” he said.
More testing of workers exposed to infected animals is also vital, experts said. Some farm owners and some individual workers have been reluctant to work with public health officials during the outbreak, experts said.
“Increased surveillance is essentially an early warning system,” Aliota said. “It helps determine the scope of the problem but also eliminates potential negative consequences.”
HOW MAJOR RISK DOES BIRD FLU PRESENT TO HUMANS?
FDA’s acting director of the Center for Food Safety, Dr. Don Prater said scientists are trying to analyze more retail milk samples to confirm that pasteurization, or heat treatment, kills the H5N1 virus. These results are expected soon.
Although the public need not worry about drinking pasteurized milk, experts said they should avoid raw or unpasteurized milk.
Aliota said dairy farm workers should also consider extra precautions such as wearing masks, washing hands and changing work clothes.
CDC officials said 23 people have been tested for the virus so far during the outbreak in dairy cows, and one person tested positive for a mild eye infection. At least 44 people exposed to infected animals in the current outbreak are being monitored for symptoms.
WHAT ARE SCIENTISTS’ CONCERNS ABOUT THE FUTURE?
David O’Connor, a virologist at the University of Wisconsin-Madison, likened the latest bird flu developments to a hurricane watch rather than a warning.
“There are certain elements that are necessary for a threat to occur, but we are not there,” he said. As with a tornado watch, “you don’t change anything about how you live your daily life, but maybe your awareness of something going on increases a little bit more.”
Worobey said this is “the kind of epidemic that we hope will not go unnoticed after COVID.” But there is.”
Ambitious screening is needed “to detect things like this very quickly and potentially nip them in the bud,” he said.
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