New analysis suggests that the H5N1 bird flu strain may have been spreading in US cattle farms since late 2023, prompting questions about America’s pathogen surveillance capabilities. This comes after the virus was detected in cows for the first time in March 2023, shortly before a human case was identified in Texas. The virus has since been identified in 36 dairy herds across eight US states, raising concerns about its ability to infect mammals.
The apparent ability of the virus to spread between cows is significant because it provides more opportunities for it to evolve and potentially infect other mammals, including humans. Of particular concern is whether H5N1 might now be able to infect pigs, which are often described as ‘mixing vessels’ for influenza and could increase the likelihood of the virus spilling 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.
Analysis of genomic data taken from the infected cattle indicates that the virus may have been circulating in the animals since late 2023. Professor Michael Worobey, a biologist at the University of Arizona who produced the analysis, said: “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.” He added: “The common ancestor may have existed around the end of 2023.”
The cattle outbreak demonstrates the need to improve pathogen surveillance in the US, according to Dr. Gerlad Parker, Associate Dean for Global One Health at the College of Veterinary Medicine & Biomedical Sciences. “The virus is more widespread than what has been reported … and has likely been circulating in cattle for some time before recognized in February, and it also tells us we must modernize surveillance systems in a one health manner that integrates animal and human health,” he said.
Currently, the World Health Organization considers the risk to humans from H5N1 to be low, but surveillance efforts must be maintained. However, experts say that the lack of accessible information released by the US Department of Agriculture (USDA) is hindering these efforts. After mounting pressure, the USDA released 239 genetic sequences of the H5N1 flu from poultry, wild birds, and dairy cows on Sunday evening, but 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,” said 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 that the 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.”
In another development, the American Association of Bovine Practitioners, a non-profit group of veterinarians, has urged government agencies and diagnostic labs to refer to the virus in cattle as ‘Bovine Influenza A Virus’, instead of H5N1. However, this move has been criticized by virologists as “unscientific and dangerous.”
The USDA has stated its commitment to the timely and transparent release of information related to the outbreak, but questions remain about the extent of the investigations conducted and the reasons behind the limited data release. Improved pathogen surveillance and collaboration between animal and human health sectors are essential to effectively monitor and mitigate the potential risks associated with the spread of H5N1.
