A highly pathogenic avian influenza has been spreading among cow herds over the country since February and has jumped species, infecting humans and chickens. Most recently, particles of the virus have been detected in pasteurized milk, but it’s not a cause for worry, according to the Food and Drug Administration, the U.S. Department of Agriculture, and several experts in food safety and risks.
The presence of the virus, even in pasteurized milk, doesn’t necessarily signify safety concerns to people, according to a statement by the FDA, due to the pasteurization process, which very likely inactivates infectious qualities of the virus, and the agencies’ work to divert and destroy milk from infected cows.
The FDA has been working closely with several other entities, including the Centers for Disease Control and Prevention and state veterinary and public health officials, to investigate the virus, which now affects 33 cow herds in eight states, according to the Department of Agriculture. Several of the entities do not anticipate significant disruptions to the supply chain of milk, including factors like availability and price, but some states are still responding to the developing virus situation by imposing restrictions and requiring veterinary clearances on cows before they cross state lines.
In a statement, the FDA explained how pasteurization, a process that uses heat to kill harmful bacteria in milk and cheese, is very likely to kill the infectious qualities of the virus and is one of the biggest reasons that even milk with a virus present can be regarded as safe to consume. “There continues to be no concern that this circumstance poses a risk to consumer health, or that it affects the safety of the interstate commercial milk supply,” the FDA wrote, “because products are pasteurized before entering the market.”
The FDA uses two different methods to test samples of milk, according to Donald Schaffner, a professor of food science at Rutgers University. To test for viral presence, the agency uses a quantitative polymerase chain reaction (qPCR) test. It uses a process called egg inoculation to test if a virus is infectious.
In the PCR test, Schaffner told Fortune, “the FDA is looking for the nucleic acid from the virus, but just because something contains viral nucleic acid doesn’t mean that it contains infectious virus.” To figure out if it’s infectious, he said, the FDA identified egg inoculation tests as the gold standard. The process involves taking a sample of milk that contains the virus and putting it into an egg. “If the virus is infectious, it will grow in the egg,” Schaffner said. According to the FDA’s statement, these tests are currently underway and those results will be made available in the “next few days to weeks,” but still, the department added, “we have seen nothing that would change our assessment that the commercial milk supply is safe.”
While research on how pasteurization effects this particular avian virus is limited, largely because this disease has never been detected in cattle before, several federal agency staff and food science experts agree that pasteurization is very likely to neutralize any infectious quality of the virus since the process has been previously studied in chicken eggs. From those prior experiments, Schaffner confirmed, “egg pasteurization gets rid of the virus in eggs,” adding that dairy milk is subjected to “a more severe pasteurization process than for eggs.”
The FDA concurred, writing that inactivation of infectious qualities of the avian flu has been “successful during the pasteurization process for eggs, which occurs at lower temperatures than what is used for fluid milk,” and that the process has “proven effective for decades against a wide range of pathogens.”
The impact and scope of the avian virus on cattle
As of today, strains of the virus have been detected in 33 herds of cows from eight states including Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota and Texas, according to the Agriculture Department.
In Texas, the virus has been widespread, affecting around 40% of cattle herds in the state’s panhandle in March. Since then, according to Sid Miller, the commissioner of Texas’s department of agriculture, about 10% of the state’s cows were at one point infected with the virus, and most recovered within a week. Disinfecting milking machines after each use, he said, has now helped his state’s farmers report zero cases of infections in the last four weeks.
“That’s just cowboy logic,” Miller said, but stated the extra cleaning has been instrumental in reducing the state’s case count of infected cows.
The cause of the virus in cows is not clear yet, according to several of the agencies. The virus situation is “very much still emerging,” Nicole Martin, an assistant research professor in dairy foods microbiology at Cornell University, told Fortune, adding that there are many unanswered questions dairy industry experts and infectious disease scientists are trying to answer. The symptoms of infected cows are analogous to a person with a cold or flu virus and cows often recover within a week or two, Martin said.
The avian virus is a much more common, and deadly, issue for poultry flocks–and can be so dangerous that infected birds are often killed to prevent its spread. Between 2022 and 2023, almost 60 million chickens and turkeys were killed on American farms for prevention purposes, but there’s no such recommendation to kill cattle since they experience much milder symptoms. The disease has also spread to other species in the past, including seals and sea lions, but infections in humans are exceedingly rare.
The most serious symptom in cows, Martin said, is decreased milk production–and in rare cases, a permanent depletion of milk.
On an individual small farm, she explained, if 20% of cows “have clinical signs of this disease, which would mean a temporary reduction in the amount of milk they’re making,” that could make a big impact. However, she said, “we don’t anticipate a major supply chain issue.”
More concerning, she said, is the virus spreading between cows in transport across the country. Moving animals from one herd to another is “somewhat commonplace across the industry,” Martin said, “and there’s a lot of states now implementing restrictions of cautionary steps prior” to the animals’ travels.
On Monday, New York State announced new temporary import requirements for dairy cattle coming in from other states. The requirements prohibit the entry of cows from areas with confirmed cases of the avian flu or areas under investigation in relation to the flu, and requires cows from affected states to have a certificate of clearance of the avian flu, issued by a veterinarian within 10 days of its entry into the state.
The certificate, Martin said, “has to include specific language that relates to this highly pathogenic avian influenza.” In her view, the mild nature of the illness, in combination with these protocols, suggest “it does not appear that there will be a major impact on the milk production overall,” across the country.
New York joins 21 other states that have implemented avian flu-related restrictions, namely Alabama, Arizona, Arkansas, California, Delaware, Florida, Hawaii, Idaho, Kansas, Kentucky, Louisiana, Maryland, Mississippi, Nebraska, North Carolina, Oregon, Pennsylvania, South Dakota, Tennessee, Utah, and West Virginia, according to the American Veterinary Medical Association.
The FDA asked farmers to monitor dairy cows for signs of illness “to ensure that milk from sick cows does not enter into interstate commerce,” and called for those who identify sick cows to work with state animal health officials to test milk samples.
Across the board, FDA officials and professors say, there is little cause for concern over nation-wide milk shortages, price hikes, or another widespread pandemic.
“For a consumer, there’s no reason to be concerned about consuming milk in the marketplace,” Martin said. “I continue to do so, and all of my colleagues continue to do so.”
