More cattle are being tested and tracked for avian influenza. What does that mean?

U.S. health and agriculture officials are ramping up testing and tracking of avian influenza in dairy cattle in an urgent effort to understand and contain the growing outbreak.

So far, the risk to humans remains low, officials said, but scientists are wary that the virus could change and spread more easily between people.

The virus, known as H5N1 type A, has been detected on nearly 30 dairy farms in eight states. Inactive virus remains have been found in milk at grocery stores. Testing also shows the virus is spreading among cattle, including those that do not show symptoms, and between cattle and birds, according to the USDA.

Starting Monday, under the terms of a new federal order, hundreds of thousands of lactating dairy cows in the United States will have to be tested and receive a negative result before they can be moved between states.

Here's what you need to know about the ongoing bird flu investigation.

This strain, known as highly pathogenic avian influenza, has been circulating in wild birds for decades. In recent years, it has been detected in numerous mammals around the world. Most of them were wild animals such as foxes and bears that ate sick or dying birds. But it's also showing up in farmed mink. It is also found in aquatic mammals such as harbor seals and porpoises. The virus has also been found in polar bears 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 been studying the virus for years.

“When you think about influenza A, cows don't usually come up in the conversation,” said Richard Webby, an influenza expert at St. Jude Children's Research Hospital.

Influenza viruses are notorious for adapting to spread among new strains, so the detection in dairy cows raises concerns that it could spread to humans, Webby said.

Scientists confirmed the virus in cattle in March, after weeks of reports from dairy farms that their cattle had become ill. Symptoms include fatigue, a sudden decrease in breast milk production, and changes in the milk, which becomes thick and yellow in color.

Matthew Aliota, a veterinary researcher at the University of Minnesota, said the discovery of virus remnants in milk on the market suggests that “this situation has been going on for longer and is more widespread than previously realized.” This suggests that there is.”

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 omitted some information about when and where the samples were taken, but the virus likely spread from birds to cattle late last year. He said that it was shown that.

Since then, the infection has spread among cows and between farms, likely through contact with physical objects such as workers' shoes, trucks and milking machines, Worobey said.

The cows then spread the virus to the birds.

“The genetic evidence is as clear as it can be,” Worobey said. “The birds sampled at these farms clearly have mammalian-adapted viruses.”

Experts said the USDA's plan to require testing of cattle is a good start.

“We need more surveillance to know what's going on,” said Thomas Friedrich, a professor of virology at the University of Wisconsin School of Veterinary Medicine.

Worobey said the ideal would be to test every herd. He said agricultural authorities not only need to check for active infections, but also whether cattle that show past infection have antibodies to the virus.

“This is a very accessible and quick way to find out how widespread this is,” he said.

Experts said further testing of workers who have been exposed to infected animals is also important. Experts say some farm owners and some independent workers are reluctant to cooperate with public health officials during the outbreak.

“Increased surveillance is essentially an early warning system,” Aliota said. “It helps characterize the scope of the problem, but also helps avoid potential negative effects.”

Scientists will now 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 Center for Food Safety. They say they are working on it. Those results are expected soon.

While the general public does not need to worry about drinking pasteurized milk, experts said raw or unpasteurized milk should be avoided.

Dairy farm workers should also consider special precautions such as masks, hand washing and changing work uniforms, Aliota said.

CDC officials said 23 people have been tested for the virus during the dairy cow outbreak, with one person testing positive for a mild eye infection. At least 44 people who had contact with infected animals in the current outbreak are being monitored for symptoms.

David O'Connor, a virology expert at the University of Wisconsin-Madison, compared the recent bird flu outbreak to tornado watches and warnings.

“There are some elements that need to exist for there to be a threat, and we're not there,” he said. As with Tornado Watch, “it won't change anything about how you go about your daily life, but it might make you a little more aware that something is going on.”

Mr Worobei said this was “the kind of epidemic that we were hoping would not be ignored after COVID-19”. But it happened. ”

He said ambitious testing was needed “to potentially catch something like this quickly and nip it in the bud.”

___

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute's Science and Education Media Group. AP is solely responsible for all content.