In early March, veterinarian Barb Petersen noticed the dairy cows she cared for on a Texas farm looked sick and produced less milk, and that it was off-color and thick. Birds and cats on the farm were dying, too. Petersen contacted Kay Russo at Novonesis, a company that helps farms keep their animals healthy and productive. “I said, you know, I may sound like a crazy, tinfoil hat–wearing person,” Russo, also a veterinarian, recalled at a 5 April public talk sponsored by her company. “But this sounds a bit like influenza to me.”
She was right, as Petersen and Russo soon learned. On 19 March, birds on the Texas farm tested positive for H5N1, the highly pathogenic avian flu that has been devastating poultry and wild birds around the world for more than 2 years. Two days later, tests of cow milk and cats came back positive for the same virus, designated 2.3.4.4b. “I was at Target with my kids, and a series of expletives came out of my mouth,” Russo said.
Now, 3 weeks into the first ever outbreak of a bird flu virus in dairy cattle, Russo and others are still dismayed—this time by the many questions that remain about the infections and the threat they may pose to livestock and people, and by the federal response. Eight U.S. states have reported infected cows, but government scientists have released few details about how the virus is spreading. In the face of mounting criticism about sharing little genetic data—which could indicate how the virus is changing and its potential for further spread—the U.S. Department of Agriculture (USDA) did an unusual Sunday evening dump on 21 April of 202 sequences from cattle into a public database. (Some may be different samples from the same animal.) And despite public reassurances about the safety of the country’s milk supply, officials have yet to provide supporting data.
The cow infections, first confirmed by USDA on 25 March, were “a bit of an inconvenient truth,” Russo says. Taking and testing samples, sequencing viruses, and running experiments can take days, if not weeks, she acknowledges. But she thinks that although officials are trying to protect the public, they are also hesitant to cause undue harm to the dairy and beef industries. “There is a fine line of respecting the market, but also allowing for the work to be done from a scientific perspective,” Russo says.
Only one human case linked to cattle has been confirmed to date, and symptoms were limited to conjunctivitis, also known as pink eye. But Russo and many other vets have heard anecdotes about workers who have pink eye and other symptoms—including fever, cough, and lethargy—and do not want to be tested or seen by doctors. James Lowe, a researcher who specializes in pig influenza viruses, says policies for monitoring exposed people vary greatly between states. “I believe there are probably lots of human cases,” he says, noting that most likely are asymptomatic. Russo says she is heartened that the Centers for Disease Control and Prevention has “really started to mobilize and do the right thing,” including linking with state and local health departments, as well as vets, to monitor the health of workers on affected farms.
As farms in more states began to report infected dairy cows last month, one theory held migratory birds were carrying the virus across the country and introducing it repeatedly to different dairy herds. But Lowe dismisses the idea as “some fanciful thinking by some cow veterinarians and some cow producers” who hoped to “protect the industry.”
Richard Webby, an avian influenza researcher at St. Jude Children’s Research Hospital, notes that available data on the virus’ genetic sequence show “no smoking guns”—mutations that could enable it to jump readily from birds to cows. At a 4 April meeting organized by a group known as the Global Framework for the Progressive Control of Transboundary Animal Diseases, Suelee Robbe Austerman of USDA’s National Veterinary Services Laboratory said “a single spillover event or a couple of very closely related spillover events” from birds is more likely. The cow virus—which USDA has designated 3.13—could then have moved between farms as southern herds were moved northward for the spring, perhaps spreading from animal to animal on milking equipment. Lowe notes that researchers at Iowa State necropsied infected cows and found no virus in their respiratory tracts, which could enable spread through the air.
USDA considers H5N1 in poultry a “program disease,” which means it is foreign to the country and subject to regulations to control it. But the agency has made no such determination for the cow disease, which means the federal government has no power to restrict movement of cattle or to require testing and reporting of infected herds or of the humans who work with them.
As a result, confusion is rife. A knowledgeable source who asked not to be identified says cattle that were healthy when they left a Texas farm appear to have brought the virus to a North Carolina farm. That raises the possibility that many cattle are infected but asymptomatic, which would make the virus harder to contain. Evidence suggests it has spread from cattle back to poultry, USDA says. Another source told Science that birds tested positive for the 3.13 strain and were culled at a Minnesota turkey farm right next to a dairy farm that refused to test its cattle.
The industry and veterinarians bear some responsibility for the confusion, Lowe says. “We didn’t even try to get ahead of this thing,” he says. “That’s a black mark on the industry and on the profession.”
Webby also faults USDA for not releasing data more quickly. The agency made six sequences from cattle—plus six related ones from birds and one from a skunk—available on the GISAID database on 29 March, 1 week after learning that cows were infected. It released one more sequence on 5 April, but then shared nothing else until the data dump 16 days later. Webby suspects the agency has moved cautiously because of the potential impact on the dairy industry. “There are a lot of people who are vested in this, and their livelihoods, at least on paper, can be impacted by whatever is found.”
Thijs Kuiken, an avian influenza researcher at Erasmus Medical Center, says the “very sparse” information released by the U.S. government has international implications, too. State and federal animal health authorities have “abundant information … that [has] not been made public, but would be informative for health professionals and scientists” in the United States and abroad, he says, “to be able to better assess the outbreak and take measures, both for animal health and for human health.” He notes that even the new sequences released by USDA do not include locations of the samples or the date they were taken. The release appears to include data from only 39 cows.
USDA said in a statement to Science that it will continue “to provide timely and accurate updates” and that its staff “are working around the clock” on a thorough epidemiological investigation to determine routes of transmission and help control spread. With its Sunday evening release, USDA made the unusual move to bypass GISAID—which requires a login and restricts how data can be used—and instead posted on a database run by the National Institutes of Health that everyone can access and do with as they please. USDA explained it did this “in the interest of public transparency and ensuring the scientific community has access to this information as quickly as possible to encourage disease research.”
The dairy industry is particularly worried that sales could suffer because of unwarranted fears that milk might infect people with the virus. The Food and Drug Administration (FDA) has said it has “no concern” that pasteurized milk presents risks because the process “has continually proven to inactivate bacteria and viruses, like influenza, in milk.”
But Lowe says for this specific virus, there are no data to back that claim. That’s “shocking,” he says. “It should not be that hard to get that data. I do not know why the foot dragging is occurring there.”
In a statement to Science, FDA said the agency is working to “reinforce our current assessment that the commercial milk supply is safe” and will share data as soon as possible. “U.S. government partners are working with all deliberate speed on a wide range of studies looking at milk along all stages of production, including on the farm, during processing and on shelves,” the statement said.
Daniel Perez, an influenza researcher at the University of Georgia, is doing his own test tube study of pasteurization of milk spiked with a different avian influenza virus. The fragile lipid envelope surrounding influenza viruses should make them vulnerable, he says. Still, he wonders whether the commonly used “high temperature, short time” pasteurization, which heats milk to about 72°C for 15 or 20 seconds, is enough to inactivate all the virus in a sample.
Lowe predicts that with increased safety precautions at farms, including more rigorous cleaning of milking equipment, and the end to the seasonal movement of cattle, this outbreak likely will die out—as often happens when bird influenza viruses infect mammals that do not make particularly good hosts.
But he and other researchers say to truly assess the continuing threat of H5N1 in cattle, they need to understand how this virus succeeded at infecting dairy cows in the first place. “Which cells is the virus replicating in? How is it getting around the body? What receptor is it using to get into cells?” Lowe wonders. “Those are the really interesting questions.”
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