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.”
Click here to see more...