The new rules call for testing unpasteurized milk from dairies across the country and for farm owners to provide details that would help officials identify and track cases more easily.The U.S. Department of Agriculture announced new rules on Friday requiring the testing of the nation’s milk supply for the bird flu virus known as H5N1, nearly a year after the virus began circulating through dairy cattle.Under the new testing strategy, the department will begin testing bulk samples of unpasteurized milk from dairy processing facilities across the country.Farmers and dairy processors will be required to provide samples of raw milk on request from the government. The rules also require farm owners with infected herds to provide details that would help officials identify more cases and contacts.The rules are a departure from the voluntary guidance that the department has 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.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.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,” he said, “and it will put us on a path to quickly controlling and stopping the virus’s spread nationwide.”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 mandate farms to share raw milk samples upon request. The 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 first round of testing under the new rules is scheduled to begin the week of Dec. 16. The program will begin in six states: California, Colorado, Michigan, Mississippi, Oregon and Pennsylvania.

Two people sharing a home caught the virus without known exposure to animals. More than 30 human cases have been reported in the United States.A Missouri resident who shared a home with a patient hospitalized with bird flu in August was also infected with the virus, federal officials reported on Thursday.But symptomatic health care workers who cared for the hospitalized patient were not infected, testing showed. The news eased worries among researchers that the virus, H5N1, had gained the ability to spread more efficiently among people.Still, the number of human cases is rising in the United States. California said this week that it had confirmed 15 human cases of bird flu. Washington State has reported two poultry workers who are infected and five others presumed to be positive.There are 31 confirmed cases in the country, but experts have said the figure is likely to be an undercount. “Additional cases may be found as investigations continue,” Dr. Nirav Shah, the principal deputy director of the Centers for Disease Control and Prevention, said at a news briefing on Thursday.“The identification of these additional cases of H5 in people with exposures to infected animals does not change C.D.C. risk assessment for the general public, which continues to be low,” he said.The poultry workers in Washington State were infected with a version of the virus that is distinct from the one circulating in dairy cattle, he added.We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.

Seven people in contact with a patient hospitalized with bird flu also developed symptoms, the C.D.C. reported. Some are undergoing further tests.A possible cluster of bird-flu infections in Missouri has grown to include eight people, in what may be the first examples of person-to-person transmission in the United States, the Centers for Disease Control and Prevention reported on Friday.If confirmed, the cases in Missouri could indicate that the virus may have acquired the ability to infect people more easily. Worldwide, clusters of bird flu among people are extremely rare. Most cases have resulted from close contact with infected birds.Health officials in Missouri initially identified a patient with bird flu who was hospitalized last month with unusual symptoms. The patient may have infected one household member and six health care workers, all of whom developed symptoms, according to the C.D.C.Investigators have not yet confirmed whether any of those seven individuals were infected with the virus, called H5N1, leaving open the possibility that they had Covid or some other illness with flulike symptoms.Still, the news alarmed experts.“We should be very concerned at this point,” said Dr. James Lawler, co-director of the University of Nebraska’s Global Center for Health Security.“Nobody should be hitting the panic button yet, but we should really be devoting a lot of resources into figuring out what’s going on.”We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.

A close contact of someone with bird flu became ill on the same day, the C.D.C. reported. But the second person was not tested, and the cause of the illness is unknown.Someone who lived with a Missouri resident infected with bird flu also became ill on the same day, the Centers for Disease Control and Prevention reported on Friday.The disclosure raises the possibility that the virus, H5N1, spread from one person to another, experts said, in what would be the first known instance in the United States.On Friday night, C.D.C. officials said that there was “no epidemiological evidence at this time to support person-to-person transmission of H5N1,” but that additional research was needed.The coincidental timing of the illnesses, especially outside flu season, concerned independent experts. H5N1 has been known to spread between close contacts, including those living in the same household.And neither the initial patient nor the household contact had any known exposure to the virus via animals or raw milk.Neither patient has been identified, and details are scant. The household contact was not tested, so officials cannot be sure that the individual actually was infected with the bird flu virus.We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.

The new case, in a Michigan farmworker, did not suggest that bird flu was widespread in people, health officials said, adding that the risk to the general public remained low.A farmworker in Michigan has been diagnosed with bird flu, state officials announced on Wednesday, making it the second human case associated with the outbreak in cows.Officials said that the individual became infected with the virus, called H5N1, after exposure to infected livestock. The individual had only mild symptoms and has fully recovered, officials said. They did not provide additional details in order to protect the privacy of the farm and farmworker, they said.In 2022, a person in Colorado with direct exposure to infected poultry became the first confirmed human case of H5N1 in the United States. Last month, the Centers for Disease Control and Prevention reported an H5N1 infection in a Texas dairy farm worker.The detection of this latest case did not suggest that bird flu was widespread in people, officials said, adding that the risk to the general public remained low.“This virus is being closely monitored, and we have not seen signs of sustained human-to-human transmission at this point,” Dr. Natasha Bagdasarian, Michigan’s chief medical executive, said in a statement.According to the C.D.C., a nasal swab from the individual had tested negative for the H5N1 virus, but an eye swab sent to the agency tested positive. Like the infected person in Texas, the Michigan patient only reported eye symptoms, the C.D.C. said.We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.

A genetic analysis sheds light on when the outbreak began, how the virus spread and where it may be going.The bird flu virus sweeping across dairy farms in multiple states has acquired dozens of new mutations, including some that may make it more adept at spreading between species and less susceptible to antiviral drugs, according to a new study.None of the mutations is a cause for alarm on its own. But they underscore the possibility that as the outbreak continues, the virus may evolve in ways that would allow it to spread easily between people, experts said.“Flu mutates all the time — it’s what, sort of, flu does,” said Richard Webby, an influenza expert at St. Jude Children’s Research Hospital, who was not involved in the work.“The real key would be if we start to see some of these mutations getting more prevalent,” Dr. Webby said. “That would raise the risk level.”The virus, called H5N1, has infected cows in at least 36 herds in nine states, raising fears that milk could be infectious — concerns now largely put to rest — and highlighting the risk that many viruses might jump across species on crowded farms.The study was posted online on Wednesday and has not been peer reviewed. It is among the first to provide details of a Department of Agriculture investigation that has been mostly opaque until now, frustrating experts outside the government.We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.

In her three decades of working with elephant seals, Dr. Marcela Uhart had never seen anything like the scene on the beaches of Argentina’s Valdés Peninsula last October.It was peak breeding season; the beach should have been teeming with harems of fertile females and enormous males battling one another for dominance. Instead, it was “just carcass upon carcass upon carcass,” recalled Dr. Uhart, who directs the Latin American wildlife health program at the University of California, Davis.H5N1, one of the many viruses that cause bird flu, had already killed at least 24,000 South American sea lions along the continent’s coasts in less than a year. Now it had come for elephant seals.Pups of all ages, from newborns to the fully weaned, lay dead or dying at the high-tide line. Sick pups lay listless, foam oozing from their mouths and noses.Dr. Uhart called it “an image from hell.”In the weeks that followed, she and a colleague — protected head to toe with gloves, gowns and masks, and periodically dousing themselves with bleach — carefully documented the devastation. Team members stood atop the nearby cliffs, assessing the toll with drones.What they found was staggering: The virus had killed an estimated 17,400 seal pups, more than 95 percent of the colony’s young animals.

Testing for H5N1 infection has been limited, and the outbreak was thought to be confined. But asymptomatic cows in North Carolina may have changed all that.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 infection 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.We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.