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.
