The bird flu, H5N1, infected dairy cows, and now fragments of the virus have been found in retail milk supplies

Most cows recover from H5N1 infections.
(Adobe Stock photo)

When remnants of the bird flu virus started showing up in U.S. retail milk supplies, dairy farmers and scientists were surprised. Now they are looking at how the virus affects cows and what its presence in drinking milk might mean for public health. "Colorado became the latest state to detect the bird flu virus spreading in dairy cattle. It follows revelations that viral fragments are turning up in retail milk," reports Will Stone for NPR. "Scientists don't view this as an immediate threat to human health. Genetic material is not the same as infectious virus, and pasteurization is expected to inactivate the virus in milk."

While the disease, also known as H5N1, is deadly to birds and some marine life, most infected dairy cows recover from bouts of bird flu. "The disease is primarily affecting older cows, which have developed symptoms that include a loss of appetite, a low-grade fever and a significant drop in milk production," report Emily Anthes and Apoorva Mandavilli of The New York Times. To treat infected cows, the Centers for Disease Control told farmers that "antiviral medications used against the seasonal flu would be effective against the H5N1 bird flu virus," reports Chuck Abbott of Successful Farming.

It's difficult for scientists to know how many cows were or are infected because, until recently, cows weren't considered at risk. Richard Webby, a virologist at St. Jude Children's Research Hospital, told Stone, "The fact that viral material is now being found in retail milk suggests this virus is probably spread around quite a bit." The fact that cows can have the disease but have no symptoms will make tracking its spread difficult. Stone reports, "Some unknown number of cattle could be shedding the virus without showing obvious symptoms. Federal health officials have confirmed this."

Does retail milk contains the infectious virus? "So far, it doesn't appear that way, but scientists who are studying this possibility acknowledge it's too soon to say that with absolute certainty," Stone explains. Lee-Ann Jaykus, a food microbiologist at North Carolina State University, told him, "There's evidence that the milk at one point in time may have had virus associated with it, but there is no evidence that that virus would be infectious, at least with the information we currently have."

"Jaykus and other scientists agree that finding viral material doesn't necessarily suggest an immediate threat to human health," Stone writes. "There is an important caveat though: There has been no direct research on how pasteurizing cow milk affects bird flu virus. Those studies are taking place right now."

When it comes to retail beef, the U.S. government is "collecting samples of ground beef at retail stores in states with outbreaks of bird flu in dairy cows for testing," reports Tom Polansek of Reuters. "But it remains confident the meat supply is safe. . . .The Department of Agriculture will analyze retail ground beef samples with PCR tests that indicate 'whether any viral particles are present,' and conduct two other safety studies, according to a statement. Some dairy cows are processed into ground beef when they grow old."