The U.S. Department of Agriculture will begin testing the nation’s milk supply for the bird flu virus known as H5N1, nearly a year after the virus began circulating through dairy cattle, the department announced on Friday.
Under the new strategy, officials will test samples of unpasteurized milk from large storage tanks at dairy processing facilities across the country.
Farmers and dairy processors will be required to provide samples of raw milk on request from the government. And farm owners with infected herds will be required to provide details that would help officials identify more cases and contacts.
The rules were first floated in October and were supposed to be implemented in November. The first round of testing is now scheduled to begin the week of Dec. 16, according to the announcement on Friday.
The new strategy is a departure from the voluntary guidance that the department had issued during the outbreak. Many dairy farms have not complied with voluntary testing of milk or of dairy workers, leaving federal officials in the dark about how widely the virus might have spread.
“I have been absolutely frustrated that we do not know the extent of the outbreak in cattle,” Seema Lakdawala, a virologist at Emory University, said.
Many experts in the United States and elsewhere, including with the World Health Organization, have sharply criticized the lack of testing of cattle and of people who may be infected with the virus. The virus does not yet spread easily among people, but every untreated infection is an opportunity for it to gain the ability to do so, experts have said.
“This effort to expand milk testing is long overdue,” said Jennifer Nuzzo, director of the Pandemic Center at Brown University School of Public Health and a vocal critic of the federal response.
“Bulk milk testing is the primary way we are identifying outbreaks on farms, which is critical for preventing severe disease for farm workers who’ve been exposed,” she said.
The virus replicates easily in the udders of cows, and raw milk from infected animals contains very high levels of the virus. At least some farm workers are thought to have become infected from droplets of milk, perhaps through their eyes.
Robert F. Kennedy, Jr., President-elect Donald J. Trump’s pick to lead the health department, has been a proponent of raw milk. California, the nation’s biggest dairy producer, recently recalled some raw milk products and halted their production after the virus was detected in some samples.
“The positive H5N1 samples from raw milk sitting on the shelves in California highlights the potential risk for milk processors who interact with milk before it’s pasteurized, and also to members of the public who consume raw milk,” said Samuel Scarpino, director of A.I. and life sciences at Northeastern University.
No one has yet been known to become ill with bird flu from drinking raw milk, although farm animals, including cats, are thought to have died after consuming contaminated milk. Pasteurized milk sold to consumers has already been shown to be free of the virus.
The new rules are an attempt to gain control over the outbreak, Agriculture Secretary Tom Vilsack said in a statement.
The strategy “will give farmers and farmworkers better confidence in the safety of their animals and ability to protect themselves, and it will put us on a path to quickly controlling and stopping the virus’s spread nationwide,” he said.
It is unclear whether the incoming Trump administration will continue the program.
“Come Jan. 21, things could change again,” said Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory.
The virus has now been detected in 720 herds in 15 states, although experts believe that figure is a significant underestimate, given the lack of mandatory testing. At least 58 people, most of them farm workers, have also been infected.
The agency’s last major mandate on testing came in April, when it issued a federal order requiring that lactating dairy cows be tested for flu before being moved across state lines.
Under the new strategy, the Agriculture Department will monitor bulk milk samples from farms nationwide, and work with state officials to identify infected herds.
The new rules also apply to private laboratories and state veterinarians, who will be required to report raw milk samples that contain virus to the Agriculture Department.
The program will begin in six states: California, Colorado, Michigan, Mississippi, Oregon and Pennsylvania.
California is currently the center of the outbreak. Colorado and Michigan have also reported many infected herds. The virus has not yet been reported in cows in Mississippi, Oregon or Pennsylvania.
It will be important to test milk in more states that have not yet identified any infected herds in order to gauge spread across the country, said Dr. Nahid Bhadelia, director of the Boston University Center on Emerging Infectious Diseases.
“I hope U.S.D.A. can quickly expand beyond the initial states mentioned,” she said.
