In the month from the federal authorities declared an outbreak of bird flu on dairy farms, have repeatedly reassured the public that the wave of infections is not affecting the nation’s food or milk supply and poses little risk to the public.
However, the outbreak among cows may be more serious than first thought. In a dark online update This week, the Department of Agriculture said there is now evidence that the virus is spreading between cows and from cows to poultry.
Officials in North Carolina have detected bird flu infections in an asymptomatic herd of cattle, The New York Times has learned — information the USDA has not publicly shared. The finding suggests that infections may be more widespread than previously thought.
Whether there are asymptomatic animals elsewhere remains unclear because the USDA does not require farms to test cattle for infection. It has reimbursed farmers for testing, but only for 20 cows per farm that were visibly sick. This week, the department said it would begin compensating farms for testing asymptomatic cows.
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 may evolve as it spreads.
They do not actively monitor infections in pigs, which are notoriously efficient hosts for the evolution of influenza viruses, and which are often kept near cattle. And the employees have he said They are not worried about the safety of the milk, despite the lack of hard data.
In joint statements in March, the USDA, the Food and Drug Administration and the Centers for Disease Control and Prevention assured the public that pasteurized milk was safe. But the FDA is still conducting tests to determine 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 argued that the milk was safe before they had the data, even though there was only a small possibility of risk to humans.
“I understand that the milk market is very concerned about losing even a few percent of milk consumption,” said Dr. Michael Osterholm, an infectious disease specialist at the University of Minnesota.
But, he added, “the idea that you can avoid these kinds of conversations by just giving absolute terms is not going to serve them well.”
The federal response so far echoes early mistakes during the pandemic, he and other experts said. “They seem to have learned few of the communication lessons that Covid taught us,” Dr Osterholm said.
In an interview this week, Dr. Rosemary Sifford, the USDA’s chief veterinarian, said more than a dozen federal epidemiologists, about twice as many laboratory workers, field staff members and academic and state partners were all involved in the investigations.
“Remember we’ve been at this for less than a month,” he said. “We are working very hard to generate more information.”
USDA staff are only analyzing viral genetic sequences from sick cows, but will release information to outside experts “in the very, very near future,” Dr. Sifford said.
“We certainly recognize that we need to learn more about the big picture,” he added.
If the department were more imminent, scientists outside the government could already be helping to contain the virus, said Dr. Tom Inglesby, director of the Johns Hopkins Center for Health Security at the Bloomberg School of Public Health.
“The days when it was considered a good plan or acceptable for a government agency to keep all the data to manage on its own are long gone,” he said.
Part of the problem, some experts said, is that the USDA has long been in the position of both regulating and promoting agricultural operations.
“We all want farms to succeed and we want to have that steady supply of food for the American consumer,” said Donn Teske, president of the Kansas Farmers Union. “But when you’re also entrusted with oversight, it’s a 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 in 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 not clear how the outbreak started on the dairy farms. Early evidence suggests there have been at least two transmissions of the virus from bird to cow, in the Texas Panhandle and New Mexico, Dr. Sifford said.
So far in cattle, the virus, called H5N1, appears to affect only lactating cows and only temporarily. There were no diagnoses in calves, pregnant heifers or veal cows, and no deaths. However, the virus appears to have spread back, from cows to poultry, in at least one case in Texas.
This infected flock and flock of poultry were on different farms. However, the virus may have been transferred between them by humans or animals that came into contact with items 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 USDA has tested relatively few animals with nasal swabs, however, and does not test feces, a common reservoir for viruses.)
Milking equipment on dairy farms is usually thoroughly 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 infected with H5N1, milk production drops sharply and the milk becomes thick and yellowish. “We’ve never seen anything like this before,” said Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory.
(Milk from infected but asymptomatic cows appears unaffected, according to a spokeswoman for the North Carolina Department of Agriculture.)
In interviews, some experts criticized the USDA’s testing recommendations, which until this week promised reimbursement only for a group of animals that were visibly sick. Farmers may not have found many infections simply because they weren’t looking for them.
Extensive testing of symptomatic and asymptomatic animals is critical early in outbreaks to understand the scale and potential mechanisms of transmission of the virus, said Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security.
Many experts noted that pigs are a linchpin in influenza surveillance, as they are susceptible to both avian and human influenza. They could act as “mixing cups,” allowing H5N1 to gain the ability to spread efficiently between humans.
The USDA does not test pigs or require farmers to do so, Dr. Sifford said.
Testing cows for H5N1 infection requires approval by a state official. Milk samples taken by an accredited veterinarian are typically tubed, packed in insulated coolers, and sent to a USDA-approved laboratory, along with a unique identifier. Positive tests are then confirmed by the USDA national laboratory in Iowa.
Each step slows down the rapid response needed to contain an outbreak, Dr Inglesby said. Testing should be easy, free and accessible, he said.
Dr. Sifford said the USDA has already received a “small number” of samples from asymptomatic cows. The department “strongly recommends testing before moving herds 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 cow blood samples to private labs to test for antibodies to the virus, which would indicate current or previous infection, said Dr. Joe Armstrong, a veterinarian at the extension University of Minnesota.
Other dairy farmers are reluctant to get tested, 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 are a lot more dairies that have had this happen than the ones we’ve sampled,” he said.
Dairy farmers are struggling with low milk prices and high feed costs, said Rick Naerebout, executive director of the Idaho Dairy Farmers Association.
“It’s already a very difficult financial situation and then to look at potentially losing 20 percent of your income over a period of two to four weeks — that really adds a lot of stress to the situation,” he said.
Idaho banned the importation of cows from the Texas Panhandle after news of the 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 federal officials should provide more resources and equipment to 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 USDA home page. The latest announcement about the outbreak from the Animal and Plant Inspection Service, a division of the department, is dated April 2.
The USDA is exploring vaccines to protect cattle against H5N1, but it is unclear how long it may take for them to develop. Dr. Armstrong, of the University of Minnesota Extension, said many farmers and veterinarians are hoping the virus will “burn itself out.”
Instead, it can become a long-term problem. “The goal is to prepare for that,” he said. “Not for that ‘it’ll just go away’ wishful thinking.”