Concern grows as bird flu spreads further in US cows: 32 herds in 8 states

Enlarge / Greylag geese sit on a field and rest while a cow walks by in the background.

Researchers around the world are increasingly concerned about the spread of highly pathogenic avian influenza (H5N1) among dairy cows in the United States, as the virus continues to find its way into new herds and into new states. Several experts say the United States is not sharing enough information about the federal investigation into the unexpected and growing outbreak, including genetic information from isolated viruses.

To date, the U.S. Department of Agriculture has identified 32 affected herds in eight states: Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota and Texas. In some cases, movement of livestock between herds can explain the spread of the virus. But the USDA has not publicly clarified whether all herds are linked in a single outbreak chain or whether there is evidence that the virus spread to cows multiple times. The first infections in Texas were linked to dead wild birds (pigeons, blackbirds and grackles) found on dairy farms. But the USDA reportedly told Stat News that not all infections appear to be linked to the Texas cases.

The spread of the virus via livestock movements indicates cow-to-cow transmission exists, the USDA said. But it’s not clear how the virus spreads between cows. Since even the most symptomatic cows show few respiratory symptoms, the USDA assumes the most likely means of spread is via contaminated milking equipment.

Adding to uncertainty about the spread of the virus, The New York Times reported Friday that the only H5N1-infected herd in North Carolina showed no symptoms of the virus. This raises the possibility that the virus could spread silently into an unknown number of other asymptomatic herds and states. In its most recent FAQ document, the USDA encourages testing for H5N1 if herds exhibit clinical symptoms, such as lethargy, fever, low milk production and loose stools. But the Times noted that the agency had begun reimbursing farms that tested asymptomatic cows.

At the same time, the USDA also said it has evidence that H5N1 from dairy farms has spread to birds on neighboring poultry farms, but how this happens is also unknown.

Data Gaps

All the uncertainty and widespread transmission is raising concerns about how the virus evolves to infect mammals and whether it makes its way to humans. Last week, the World Health Organization’s chief scientist, Jeremy Farrar, told reporters in Geneva that the spread of the virus among U.S. dairy cows was a “huge concern,” according to CNN. “The big concern, of course, is that by infecting ducks and chickens in this way – but now increasingly mammals – this virus evolves and develops the ability to infect humans. And then, crucially, the ability to pass from human to human transmission.

In particular, experts fear that outbreaks in dairy cows could spread to nearby pig farms, as is the case with nearby poultry farms. Pigs can be infected with both avian influenza viruses and human influenza viruses, making them potential breeding grounds for new recombinant influenza strains.

So far, the USDA says genetic sequences of the H5N1 virus infecting cows have not revealed any mutations that “would make it more transmissible to humans and between humans.” But last Thursday, Stat reported that international experts had criticized the USDA for not sharing more genetic data from its investigation, among other information. Until this weekend, the agency had shared only a few genetic sequences in an international viral genome sequence database (GISAID).

“A country with capabilities like the United States should be able to generate this information within a few days,” Marion Koopmans, head of the viroscience department at the Erasmus Medical Center in the Dutch city of Rotterdam, told Stat last week. “I would expect very quick and very transparent updates, and it’s somewhat surprising to not see that happening.”

On Sunday, in the face of growing criticism, the USDA announced the release of 239 genetic sequences to GISAID. It said it was also adding raw data to a U.S. federal database “in the interest of public transparency and to ensure that the scientific community has access to this information as quickly as possible.” The agency said it will continue to make this data available on an ongoing basis.

Dr. Rosemary Sifford, the USDA’s chief veterinarian, told the Times: “Remember, we’ve been working on this for less than a month. We’re working very hard to generate more information.” she declared.

Overall, the USDA and the U.S. Centers for Disease Control and Prevention continue to consider the risk to the public to be low. Farm workers and others in direct contact with infected animals, however, are encouraged to take precautions.

Although deadly to birds, H5N1 in cows is relatively benign and rarely, if ever, causes death. Milk from sick animals contains high levels of virus, but it is being destroyed. Even if infected milk found its way into the milk supply, the Food and Drug Administration is confident the virus would be killed during the pasteurization process. “Pasteurization has continually been shown to inactivate bacteria and viruses, such as influenza, in milk,” the agency said in an FAQ Friday. Some experts, however, have called for data confirming this.

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Gn Health

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