New reports saying that dairy herds in Nevada, U.S. have been infected by a version of the H5N1 bird flu not previously seen in cows, has put virologists and researchers on high alert. Among other things, the news from the Nevada Department of Agriculture, suggests that driving the virus out of the U.S. cattle population won’t be nearly as simple as federal officials once suggested — or perhaps hoped.
On 7 February 2025, there came a second and potentially more serious blow: A technical brief by the U.S. Department of Agriculture reported that the genotype, known as D1.1, contains a genetic mutation that may help the virus more easily copy itself in mammals — including humans.
This D1.1 version of the virus is the same variant that killed a man in Louisiana and left a Canadian teen hospitalized in critical condition. It is not the B3.13 genotype widely found in sick cattle dating to early last year.
"This can be of significant concern if this virus continues to spread among cows and infects more people," immunologist and former federal health official Rick Bright tells Fortune.
"This mutation has not been associated with improved human transmission, so there are no telling signs of enhanced spread yet. But when this virus gets into people, it is ready to cause a much more serious disease than the (B3.13) virus that has been circulating in cows before now.
"We have never been closer to a pandemic from this virus," Bright adds. "And we still are not doing everything possible to prevent it or reduce the impact if it hits."
The D1.1 genotype has been detected in wild birds in all North American flyways, as well as mammals and poultry, so it isn’t surprising that it’s made the leap to cows. But its newfound presence in the Nevada dairy herds is considered by many virologists to mark a sort of inflection point in the spread of H5N1, and it could spell more trouble for humans going forward.
"Given the fact that D1.1 seems to be more virulent in humans, this could indicate a major change in terms of public health risks from the earlier scenario with the B3.13 strain," veterinary science pioneer Juergen Richt, a former director at the National Institutes of Health, tells Fortune.
In response to an emailed series of questions, a spokesperson for the federal Centers for Disease Control and Prevention (CDC) said the agency still deems the risk to human health for the general public to be low. "However, people with close, prolonged, or unprotected exposures to infected birds or other animals (including livestock), or to environments contaminated by infected birds or other animals, are at greater risk of infection," the spokesperson said.
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