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Cats suffer H5N1 brain infections, blindness, death after drinking raw milk

bird flu, Cats, cows, dairy cows, H5N1, health, herds, infectious diseases, influenza, milk, Science / /

Spillover —

Mammal-to-mammal transmission raises new concerns about the virus’s ability to spread.

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Farm cats drinking from a trough of milk from cows that were just milked.

Enlarge / Farm cats drinking from a trough of milk from cows that were just milked.

On March 16, cows on a Texas dairy farm began showing symptoms of a mysterious illness now known to be H5N1 bird flu. Their symptoms were nondescript, but their milk production dramatically dropped and turned thick and creamy yellow. The next day, cats on the farm that had consumed some of the raw milk from the sick cows also became ill. While the cows would go on to largely recover, the cats weren’t so lucky. They developed depressed mental states, stiff body movements, loss of coordination, circling, copious discharge from their eyes and noses, and blindness. By March 20, over half of the farm’s 24 or so cats died from the flu.

In a study published today in the journal Emerging Infectious Diseases, researchers in Iowa, Texas, and Kansas found that the cats had H5N1 not just in their lungs but also in their brains, hearts, and eyes. The findings are similar to those seen in cats that were experimentally infected with H5N1, aka highly pathogenic avian influenza virus (HPAI). But, on the Texas dairy farm, they present an ominous warning of the potential for transmission of this dangerous and evolving virus.

The contaminated milk was the most likely source of the cat’s fatal infections, the study authors concluded. Although it can’t be entirely ruled out that the cats got sick from eating infected wild birds, the milk they drank from the sick cows was brimming with virus particles, and genetic data shows almost exact matches between the cows, their milk, and the cats. “Therefore, our findings suggest cross-species mammal-to-mammal transmission of HPAI H5N1 virus and raise new concerns regarding the potential for virus spread within mammal populations,” wrote the authors, who are veterinary researchers from Iowa, Texas, and Kansas.

The early outbreak data from the Texas farm suggests the virus is getting better and better at jumping to mammals, and data from elsewhere shows the virus is spreading widely in its newest host. On March 25, the US Department of Agriculture confirmed the presence of H5N1 in a dairy herd in Texas, marking the first time H5N1 had ever been known to cross over to cows. Since then, the USDA has tallied infections in at least 34 herds in nine states: Texas, Kansas, Michigan, New Mexico, Idaho, Ohio, South Dakota, North Carolina, and Colorado.

The Food and Drug Administration, meanwhile, has detected genetic traces of H5N1 in roughly 20 percent of commercial milk samples. While commercial milk is still considered safe—pasteurization is expected to destroy the virus and early testing by the FDA and other federal scientists confirms that expectation—the finding suggests yet wider spread of the virus among the country’s milk-producing cows.

Cows are only the latest addition to H5N1’s surprisingly broad host range. Amid a global outbreak over the past several years that has devastated wild bird populations and poultry farms, researchers have documented unexpected and often deadly outbreaks in mammals. Since 2022, the USDA has found H5N1 in over 200 mammals, from big cats in zoos to harbor seals, mountain lions, raccoons, skunks, squirrels, polar bears, black bears, foxes, and bottlenose dolphins.

“The recurring nature of global HPAI H5N1 virus outbreaks and detection of spillover events in a broad host range is concerning and suggests increasing virus adaptation in mammals,” the authors wrote. “Surveillance of HPAI viruses in domestic production animals, including cattle, is needed to elucidate influenza virus evolution and ecology and prevent cross-species transmission.”

In the meantime, it’s definitely not the time to start drinking raw cow’s milk. While drinking raw milk is always dangerous because it carries the threat of various nasty bacterial infections, H5N1 also appears to be infectious in raw milk. And, unlike other influenza viruses, H5N1 has the potential to infect organs beyond the lungs and respiratory tract, as seen in the cats. The authors of the new study note that a 2019 consumer survey found that 4.4 percent of adults in the US consumed raw milk more than once in the previous year, suggesting more public awareness of the dangers of raw milk is necessary.

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

avian influenza, bird flu, CDC, cows, dairy cows, fda, H5N1, herds, infection, milk, outbreak, Science, USDA, virus / /

Rapidly evolving —

Experts say the US is not sharing as much data on the outbreak as it should.

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Greylag geese sit on a field and rest while a cow passes by in the background.

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

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

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

Spread of the virus via cattle movements indicates that there is cow-to-cow transmission occurring, the USDA said. But it’s unclear how the virus is spreading between cows. Given that even the most symptomatic cows show few respiratory symptoms, the USDA speculates that the most likely way it is spreading is via contaminated milking equipment.

Adding to the uncertainty of the virus’s spread, The New York Times on Friday reported that the one herd found infected with H5N1 in North Carolina showed no symptoms of the virus. This raises the possibility that the virus could be silently spreading in unknown numbers of other asymptomatic herds and states. In its most recent FAQ document, the USDA encouraged testing for H5N1 if herds show clinical symptoms, such as lethargy, fever, low milk production, and loose stools. But the Times noted that the agency has begun reimbursing farms for testing asymptomatic cows.

Meanwhile, the USDA also reported that it has evidence that H5N1 from dairy farms has spread back into birds in nearby poultry farms, but how this is happening is also unknown.

Data gaps

All the uncertainty and widespread transmission raises concern about how the virus is evolving to infect mammals and whether it is heading for humans. Last week, the chief scientist for the World Health Organization, Jeremy Farrar, told reporters in Geneva that the spread of the virus in US dairy cows is an “enormous concern,” according to CNN.  “The great concern, of course, is that in doing so and infecting ducks and chickens—but now increasingly mammals—that that virus now evolves and develops the ability to infect humans. And then critically, the ability to go from human-to-human transmission.”

In particular, experts are wary that the dairy cow outbreaks could spill over to nearby pig farms as it’s doing with nearby poultry farms. Pigs can be infected with both bird flu viruses and human flu viruses, making them potential melting pots for new recombinant flu strains.

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

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

On Sunday, facing mounting criticism, the USDA announced the release of 239 genetic sequences to GISAID. It noted it is also adding raw data to a US federal database “in the interest of public transparency and ensuring the scientific community has access to this information as quickly as possible.” The agency said it will continue to make such data available on a rolling basis.

Dr. Rosemary Sifford, the USDA’s chief veterinarian, told the Times, “Please recall that we’ve been engaged in this for less than a month. We are working very hard to generate more information,” she said.

Overall, the USDA and the US Centers for Disease Control and Prevention continue to consider the risk to the public to be low. Farmworkers and others who have direct contact with infected animals are encouraged to take precautions, however.

While deadly to birds, H5N1 in cows is relatively mild, rarely if ever causing deaths. Milk from sick animals contains high levels of virus, but it is being destroyed. Even if some infected milk makes its way into the milk supply, the Food and Drug Administration is confident that the virus would be killed in the pasteurization process. “Pasteurization has continually proven to inactivate bacteria and viruses, like influenza, in milk,” the agency said in an FAQ Friday. Some experts have called for data confirming this, though.

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