Bird flu ‘likely spreading in cows since last year’ as concern grows over US virus detection systems

There is a “strong possibility” that bird flu has been spreading in US cattle farms since last year, new analysis suggests, prompting questions about America’s pathogen surveillance capabilities.

Last month, the H5N1 strain was spotted in cows for the first time, shortly before a human case was detected in Texas. The virus, which has killed tens of millions of birds worldwide since 2020, was subsequently identified in 36 dairy herds across eight US states, raising concerns about its ability to infect mammals.

US health officials released genomic data taken from the infected cattle on Sunday, having previously said there is evidence of H5N1 spreading between cows. However, analysis of the data now indicates the virus may have been circulating in the animals since late 2023.

“It looks to me like a strong possibility that this has been circulating in cattle for months under our noses, even before the first inkling there might be something new in February,” said Professor Michael Worobey, a biologist at the University of Arizona who produced the analysis.

“This common ancestor may have existed around the end of 2023,” he added on X (formerly Twitter). “The common ancestor may have been in cattle, with only a single intro into cattle and subsequent spread. But we can’t rule out multiple jumps, later, from a largely avian reservoir.”

The apparent ability of the virus to spread between cows is significant because it provides more opportunities for it to evolve to better infect other mammals, potentially including humans.

Of particular concern is whether H5N1 might now be able to infect pigs, often described as ‘mixing vessels’ for influenza and making it more likely that the virus could spill over into humans.

There have also been unconfirmed reports that the virus has jumped from cows back to birds, highlighting the potential threat of recombination – when different viruses merge and mix their properties together to create a new strain.

Dr Gerald Parker, Associate Dean for Global One Health at the College of Veterinary Medicine & Biomedical Sciences, said the cattle outbreak demonstrated the need to improve pathogen surveillance in the US.

“The virus is more widespread than what has been reported … and has likely been circulating in cattle for some time before recognised in February, and it also tells us we must modernise surveillance systems in a one health manner that integrates animal and human health,” he said.

Questions over cattle industry

At present, the World Health Organization has said the risk to humans is still considered low, but that surveillance efforts must be kept up – something that is being potentially hindered by the lack of accessible information released by the US Department of Agriculture (USDA), experts say.

After mounting pressure, USDA released 239 genetic sequences of the H5N1 flu from poultry, wild birds, and dairy cows on Sunday evening, which scientists hoped would allow them to look for new clues about the virus’s spread.

However, the data was released without any information indicating where and when each animal was infected.

“It creates unnecessary delays and further is likely not a complete set of all the sequence data USDA has collected so far,” Dr Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan, who was involved in the analysis by Prof Worobey’s team.

“It’s important to figure out how this got into the cattle and the mechanism by which it’s spreading in them, but the incomplete metadata is ultimately an obstacle to that goal.”

Some believe USDA is not being forthcoming with information to protect the cattle industry’s commercial interests.

Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy, said: “The USDA is primarily focused on protecting the animal production industry, and I think that’s a short-term goal, but a long-term mistake.”

At this stage, it is also unclear what investigations the USDA has carried out, further clouding any understanding over how the cows became infected, Mr Osterholm added.

Peter Bogner, the founder of GISAID, an international database that keeps track of dangerous new flu strains, said: “Given the pandemic potential posed by highly pathogenic avian influenza viruses, the timely sharing of data of the recent H5N1 outbreak reported in Texas is crucial.”

In another development, the American Association of Bovine Practitioners, a non-profit group of veterinarians, released a statement last week urging government agencies, diagnostic labs, and federal agencies to refer to the virus in cattle as ‘Bovine Influenza A Virus’, instead of H5N1.

In a public letter, the organisation said this is because they “believe it is important for the public to understand the difference to maintain confidence in the safety and accessibility of beef and dairy products for consumers,” a move that has been slammed as “unscientific and dangerous” by virologists.

The Telegraph approached the USDA for comment but did not receive a response.

However, a spokesperson told Stat magazine: “USDA has been committed to the timely and transparent release of information related to the outbreak as it becomes available. We will continue to work to provide timely and accurate updates to the public, our stakeholders, and the scientific community as we learn more.”

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