In the month since federal authorities announced an outbreak of bird flu on dairy farms, they have repeatedly reassured the public that the spate of infections does not impact the nation’s food or milk supply, and poses little risk to the public.
Yet the outbreak among cows may be more serious than originally believed. In an obscure online update this week, the Department of Agriculture said there is now evidence that the virus is spreading among cows, and from cows to poultry.
Officials in North Carolina have detected bird flu infections in a cattle herd with no symptoms, The New York Times has learned — information the U.S.D.A. has not shared publicly. The finding suggests that the infections may be more widespread than thought.
Whether there are asymptomatic animals elsewhere remains unclear, because the U.S.D.A. is not requiring farms to test cattle for infection. It has been reimbursing farmers for testing, but only for 20 cows per farm that were visibly ill. This week, the department said it would begin reimbursing farms for testing cows without symptoms.
Federal officials have shared limited genetic information about the virus with scientists and with officials in other countries, which is important for learning how the virus might be evolving as it spreads.
They are not actively monitoring infections in pigs, which are famously effective hosts for evolving flu viruses, and which are often kept in proximity to cattle. And officials have said they have “no concern” about the safety of milk, despite a lack of hard data.
In joint statements in March, the U.S.D.A., the Food and Drug Administration and the Centers for Disease Control and Prevention assured the public that pasteurized milk was safe. But the F.D.A. is still conducting tests to ascertain whether the process eliminates the virus. The agency declined to say when results from those tests would be available.
Some experts said the agencies should not have asserted that the milk is safe before they had the data in hand, even though there is only a slim chance of risk to people.
“I understand that the milk market is very concerned about a loss of even a few percent of milk consumption,” said Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota.
But, he added, “the idea that you can avoid this kind of discussion by just giving absolutes is not going to serve them well.”
The federal response so far echoes early missteps during the pandemic, he and other experts said. “It seems they learned little from the communication lessons that Covid taught us,” Dr. Osterholm said.
In an interview this week, Dr. Rosemary Sifford, the U.S.D.A.’s chief veterinarian, said that more than a dozen federal epidemiologists, roughly twice as many laboratory employees, field staff members and academic and state collaborators were all involved in the investigations.
“Please recall that we’ve been engaged in this for less than a month,” she said. “We are working very hard to generate more information.”
U.S.D.A. staff are analyzing only viral genetic sequences from sick cows, but will release information for outside experts “in the very, very near future,” Dr. Sifford said.
“We definitely recognize that we need to learn more about the overall picture,” she added.
If the department were more forthcoming, scientists outside the government could already be helping to contain the virus, Dr. Tom Inglesby, director of the Johns Hopkins Center for Health Security at the Bloomberg School of Public Health, said.
“The days when it was seen as a good plan or acceptable for a government agency to keep all data to manage on its own are gone long ago,” he said.
Part of the problem, some experts said, is that the U.S.D.A. has long been in the position of both regulating and promoting the business of agriculture.
“We all want farms to succeed, and we want to have that steady food supply for the American consumer,” said Donn Teske, president of the Kansas Farmers Union. “But then when you are also tasked with the oversight, it’s a little bit of an issue there.”
The current version of the bird flu virus has been circulating since 2020 in poultry, wild birds and more recently, a wide range of mammals.
As of Friday afternoon, the outbreak in dairy cows had spread to 32 herds in eight states: Texas, New Mexico, Michigan, Kansas, Idaho, Ohio, North Carolina and South Dakota.
It is unclear how the outbreak began on dairy farms. Early data suggest that there were at least two spillovers of the virus from bird to cow, in the Texas Panhandle and New Mexico, Dr. Sifford said.
So far among cattle, the virus, called H5N1, seems only to affect lactating cows, and only temporarily. There have been no diagnoses in calves, pregnant heifers or beef cows, and no deaths. But the virus appears to have spilled back, from cows to poultry, in at least one instance in Texas.
That infected herd and poultry flock were on different farms. But the virus may have been transported between them by people or animals that had contact with objects contaminated with virus-laden milk, according to the Texas Animal Health Commission.
Infected cows appear to carry large amounts of the virus in their milk. (The U.S.D.A. has tested relatively few animals by nasal swab, however, and is not testing feces, a common repository for viruses.)
Milking equipment on dairy farms is typically deep-cleaned, but not sterilized, at least once a day. People milking cows are encouraged to wear safety glasses, or masks or face shields, but the recommendations are often ignored.
In cows sickened by H5N1, milk production drops sharply, and the milk becomes viscous and yellowish. “We’ve never seen something like this before,” said Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory.
(Milk from infected but asymptomatic cows seems unchanged, according to a spokeswoman for the North Carolina agriculture department.)
In interviews, some experts criticized the U.S.D.A.’s testing recommendations, which until this week promised reimbursement only for a pool of animals that were obviously ill. Farmers may not have found many infections simply because they were not looking for them.
Widespread testing of animals with and without symptoms is crucial early in outbreaks to understand the scale and the possible mechanisms of viral transmission, said Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security.
Pigs are a linchpin in flu surveillance, many experts noted, as they are susceptible to both bird and human flu. They might act as “mixing bowls,” enabling H5N1 to acquire the ability to spread efficiently among people.
The U.S.D.A. is not testing pigs or asking farmers to do so, Dr. Sifford said.
Testing cows for H5N1 infection requires approval from a state official. Milk samples obtained by an accredited veterinarian are typically packaged in tubes, packed in insulated coolers, and shipped to a U.S.D.A.-approved lab, along with a unique identifier. Positive tests are then confirmed by the U.S.D.A.’s national lab in Iowa.
Each step slows the speedy response needed to contain an outbreak, Dr. Inglesby said. Testing should be easy, free and accessible, he said.
Dr. Sifford said the U.S.D.A. has already received a “small number” of samples from cows without symptoms. The department is “strongly recommending testing before herds are moved between states, which includes asymptomatic herds,” an agency statement said.
Already some state health departments and farmers have grown frustrated with the federal approach. Several farms in Minnesota — not one of the eight states with known cases — are sending samples of cow blood to private labs to test for antibodies to the virus, which would indicate a current or past infection, said Dr. Joe Armstrong, a veterinarian at the University of Minnesota Extension.
Other dairy farmers are reluctant to test, worried that fears about bird flu could hurt their business, said Dr. Amy Swinford, director of the Texas A&M Veterinary Medical Diagnostic Laboratory.
“I think there’s many more dairies that have had this going on than what we’ve gotten samples from,” she said.
Dairy farmers are grappling with low milk prices and high feed costs, said Rick Naerebout, chief executive of the Idaho Dairymen’s Association.
“It’s already a very difficult economic situation, and then to look at possibly losing 20 percent of your revenue for a period of two to four weeks — that’s really adding a lot of anxiousness to the situation,” he said.
Idaho barred the importation of cows from the Texas Panhandle after news of bird flu outbreak there, but a week too late. Having an infected herd in Idaho despite those precautions “was kind of a gut shot,” Mr. Naerebout said.
Matt Herrick, a spokesman for the International Dairy Foods Association, said that federal officials should provide more resources and equipment for farmers to protect themselves, and should publicize updates more widely, including through social media.
There is no mention of the bird flu outbreak on the U.S.D.A.’s homepage. The last outbreak-related announcement from the Animal and Plant Health Inspection Service, a division of the department, is dated April 2.
The U.S.D.A. is exploring vaccines to protect cattle from H5N1, but it is unclear how long it might take to develop them. Dr. Armstrong, of the University of Minnesota Extension, said many farmers and veterinarians hope the virus will “burn itself out.”
Instead, it may become a long-term problem. “The goal is to prepare for that,” he said. “Not for this wishful thinking of, ‘It’ll just go away.’”
