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Avian Flu’s Recent Spread ‘Changes the Rules of the Game’

After Human Case Confirmed, UMD Expert Warns: Mammal-to-Mammal Infection Require More Safeguards

By Chris Carroll

bird stands in front of cows on a dairy farm

Dairy cows face off with a bird near Vado, N.M. Tests showed cows in the state have bird flu, the USDA announced Monday.

AP Photo/Rodrigo Abd, File

When the avian flu known as H5N1 spreads from birds to other species, the infected animal typically recovers or dies without passing on the virus. But in a surprising twist last week, scientists discovered that dairy cows in Texas apparently spread H5N1, or avian flu, to a farm worker who later tested positive, and might have been spreading it among themselves, the U.S. Department of Agriculture (USDA) announced on Monday.

Since then, cows in Kansas, New Mexico and Idaho have also fallen ill; the disease—which has killed millions of poultry animals worldwide since 2022—is also suspected in Idaho. No other human cases have so far been announced.

None of the affected mammals, bovine or human, appears to be seriously ill, and no infections have been reported in Maryland, but the development is still cause for worry, said Mostafa Ghanem, an assistant professor of veterinary medicine at the University of Maryland who studies infectious disease.

“If it’s proven this kind of lateral transmission is occurring in mammals, that changes the rules of game,” Ghanem said. “It’s very concerning, and it means more, and more complex, measures are going to be needed to guard against it.”

He spoke on Tuesday to Maryland Today about safety measures that farms can take, how avian flu has changed and whether our milk supply is at risk.

The latest infections put us in uncharted territory.

Prior to the March 25 announcement about the Texas farm, no dairy cows had ever been infected by bird flu, let alone transmitted it to other cows, according to the USDA. The as-yet unproven possibility that they spread it to a farm worker who came in contact with them pushes the case further beyond the norm, Ghanem said. In the United States, only one person had ever been infected by bird flu, in 2022, and the only other ruminant animal that contracted it was a baby goat. In addition, he said, while H5N1 is an RNA virus that’s “highly prone to evolution and changing all the time,” in the recent cases, analysis has shown no indication that a virus mutation made it better able to infect mammal hosts or spread more easily among people—a good thing, he said.

H5N1 is a killer—but rarely of cows or humans.

Avian influenza is most deadly to domestic poultry, where mortality can approach 100% in some outbreaks, and is generally spread by wild fowl, which can be infected and recover, or even remain largely asymptomatic. The infected dairy cows may have a fever, give less milk or poor-quality milk and eat less. The only symptom shown by the man infected in Texas, meanwhile, is a mild case of conjunctivitis, aka pink eye. Human infections with avian influenza A viruses, including H5N1, are uncommon but have occurred sporadically worldwide, and the risk of infection for general public remains low, Ghanem said.

Avian flu has changed
UMD-led research in recent years has shown that what used to be a seasonal flu is increasingly taking on a year-round character. “We’ve had avian flu over the summer the past two years, which means things are changing and the time of risk is lasting longer and longer,” Ghanem said. The avian flu outbreak that has been surging since 2022 has poultry farmers boosting biosecurity measures to keep chickens and other species away from wild birds—measures that in large part have proven effective, he said.

Farmers—and backyard chicken farmers—must boost their vigilance.

Cattle operations may now have to grapple with similar considerations as poultry operations, managing wild bird contact with herds and protecting water sources from contamination by birds—the route by which the Texas cattle are suspected to have been infected. Finally, farmers must closely monitor data on cows’ feeding, milk production and other behaviors. “It’s pretty easy to see when something is wrong,” he said. “But it will be crucial to quarantine that animal until you have test results to avoid spreading through the herd.”

In addition, the rising number of infected wild birds is increasing the chance that the heritage breed hens that provide your breakfast eggs could fall victim to the virus, meaning it’s time to take steps to avoid attracting wild birds to your property, and keep your poultry security enclosed.

Our food is safe.

Milk from sick cows isn’t allowed into the food supply, Ghanem said, and regardless, any milk that’s part of interstate commerce is required to be pasteurized. That treatment kills any potentially infectious microbes, just as cooking meat to a safe temperature does, he said. In addition, he said, the situation is being closely monitored nationwide, with health authorities taking necessary precautions to prevent further spread of the virus and protect animals and food supply.



Maryland Today is produced by the Office of Marketing and Communications for the University of Maryland community on weekdays during the academic year, except for university holidays.