How worrying is bird flu's jump to dairy cows? Here's what experts say

In the meantime, the USDA and the FDA both say that pasteurization has proven to kill viruses and bacteria, and there is no risk of infection from drinking commercial milk. And so far, the limited number of cases, plus cows’ relatively quick recovery from infection means there’s no threat to the country’s milk supply, for now.

Raw milk from sick cattle, however, has tested positive for the virus, and the CDC has urged people not to consume raw, unpasteurized milk. Dairy advocacy groups, like the Dairy Alliance, which represents farmers in Georgia and other Southeastern states, are echoing that sentiment.

“With raw milk, it’s always a risk, regardless of this virus,” said Geri Berdak, CEO of the Dairy Alliance, which counts roughly 75 farms in Georgia among its members. “There are absolutely no safety concerns with pasteurized milk.”

Why are cow cases worrisome?

Most humans aren’t regularly in close proximity to wild birds or many of the other mammals that have contracted bird flu during the current outbreak.

But cows are a domesticated species regularly in close contact with people on farms. That is troubling to Seema Lakdawala, an associate professor of microbiology and immunology at Emory University.

“I’m always concerned when bird viruses are getting into mammals ... but the cows are concerning because like pigs, they have a really extensive contact network,” said Lakdawala.

Pigs, which are vulnerable to both avian and flu viruses, have long been identified as a potential “mixing vessel,” where bird and human influenza viruses could recombine to create a new strain that spreads more effectively from person-to-person. So far, there’s no evidence this is occurring.

While bird flu has appeared in many mammal species during the current outbreak, cows were not considered likely candidates to catch the disease, experts say. Virologists have long known cattle were vulnerable to influenza type D viruses, but not influenza A viruses like the current bird flu strain, Lakdawala said. Influenza A is one of two main subtypes that typically cause illness in humans.

David Skallnecht, a professor emeritus at the University of Georgia’s College of Veterinary Medicine, said he didn’t expect cattle to catch the virus, but was not terribly shocked that they had.

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