by US health and agriculture officials are testing and tracking bird flu in dairy cows in an urgent effort to understand – and stop – the growing outbreak.
So far, the risk to people is still low, officials said, but scientists are wary that the virus could change to spread more easily among 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 between cows, including those that do not show symptoms, and between cows and birds, according to the US Department of Agriculture.
Starting Monday, hundreds of thousands of lactating dairy cows in the US will be tested – with negative results – before they can be moved between states, under the terms of a new federal order.
Here’s what you need to know about the ongoing bird flu investigation:
WHY IS THIS REGION SO UNUSUAL?
This highly pathogenic strain of bird flu has been circulating in wild birds for many years. In recent years, it has been observed in scores of mammals around the world. Most were wild animals, such as foxes and bears, who ate sick or dying birds. But it also appears in cultivated minks. It has also been shown 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 ruminants – goats and then dairy cows – in the United States this spring, surprising many scientists who have studied it for years.
“When we think about influenza A, we don’t usually include cows in that conversation,” said Richard Webby, an influenza expert at St. John’s Children’s Research Hospital. Jude.
Influenza viruses are known for adapting to spread among new species, so detection in dairy cows raises concerns that it could spread to humans, Webby said.
HOW LONG DOES BIRD FLU LIVE?
Scientists confirmed the virus in cows in March after weeks of reports from dairy farms that the animals were sick. Symptoms included lethargy, a sharp decrease in milk supply and changes in the milk, which became thick and yellow.
Finding remnants of the virus in marketed milk “suggests that this is going on longer, and is more widespread, than we previously recognized,” said Matthew Aliota, a researcher on medicine of veterinary medicine at the University of Minnesota.
Under pressure from scientists, USDA officials released new genetic data about the outbreak this week.
The data left out some information about when and where samples were collected, but indicated that the virus was likely spread by birds to cattle late last year, said Michael Worobey, an evolutionary biologist at the University of Arizona.
Since then, it has spread among cattle and farms, likely through contact with physical objects such as workers’ shoes, trucks or milking machines, Worobey said.
And then the cows spread the virus back to birds, he said.
“The genetic evidence is as clear as it gets,” Worobey said. “Birds sampled on these farms have viruses with clear mammalian adaptations.”
WHAT DOES SCIENCE SAY ABOUT THE EFFORTS TO CONTROL PREGNANCY?
Some experts said the USDA’s plans to require testing of cows are a good start.
“We need to be able to do better surveillance so we know what’s going on,” said Thomas Friedrich, a professor of virology at the University of Wisconsin’s veterinary school.
Worobey said the ideal is to screen every herd. Rather than looking for active infections, agriculture officials should be looking to see if cows have antibodies to the virus, which indicate past infections, he said.
“That’s a really accessible and quick way to find out how widespread this is,” he said.
Further testing of workers exposed to infected animals is also critical, experts said. Some farm owners and some individual workers were reluctant to work with public health officials during the outbreak, experts said.
“Increased surveillance is essentially an early warning system,” Aliota said. “It helps to characterize the scope of the problem, but also to eliminate potentially harmful consequences.”
HOW BIG OF A RISK IS BIRD FLU TO HUMANS?
Scientists are working to analyze more samples of retail milk to confirm that pasteurization, or heat treatment, kills the H5N1 virus, said Dr. Don Prater, acting director of the FDA’s food safety center. Those results are expected soon.
While the general public need not worry about drinking pasteurized milk, experts said they should avoid raw or unpasteurized milk.
Also, dairy farm workers should take extra precautions, such as covering up, washing hands and changing work clothes, Aliota said.
So far, 23 people have been tested for the virus during the outbreak in dairy cows, and one person tested positive for a mild eye infection, CDC officials said. At least 44 people exposed to infected animals in the current outbreak are being monitored for symptoms.
WHAT DOES INTERNATIONAL KNOWN FOR THE FUTURE?
David O’Connor, a virology expert at the University of Wisconsin-Madison, compared recent bird flu developments to a tornado watch versus a warning.
“There are some of the ingredients that would be necessary for there to be a threat, but we are not there,” he said. As with a tornado watch, “you wouldn’t change anything about how you live your daily life, but you might have a little awareness that something is happening.”
Worobey said this is the type of outbreak that “we hoped, after COVID, would go unnoticed. But yes.”
He said that ambitious screening is needed “to detect things like this very quickly, and to be able to eliminate them.”
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The Associated Press Health and Science Section is supported by the Howard Hughes Medical Institute Science and Media Education Group. The AP is solely responsible for all matters.
