Dairy cattle in the United States have tested positive for a particular strain of bird flu that was not previously found in cows, the US Department of Agriculture said, on Wednesday.
According to CNN, in Nevada, six herds have been detected with a newer strain (D1.1) of the H5N1 bird flu virus has previously been detected only in birds and in people who had contact with infected birds.
The D1.1 strain has been linked to two severe human infections: a teenager in British Columbia who was hospitalised in critical condition last fall but later recovered, and a senior in Louisiana who succumbed to the infection in January. In Washington state, farmed also tested positive for D1.1 after culling infected poultry but their symptoms were described as milder.
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The D1.1 strain has recently emerged as the dominant variant, spreading among wild birds and poultry flocks across North America, the report said. It was identified in dairy cattle through an agency program that began testing milk for bird flu in December.
“We’re seeing the H5N1 virus itself be smarter than all of us,” said Beth Thompson, South Dakota’s state veterinarian told Reuters.
“It’s modifying itself so it’s not just staying in the poultry and the wild waterfowl. It’s picking up a home in the mammals,” she added.
According to CNN, scientists are studying the D1.1 strain to understand its capabilities and how it appears to be spreading so aggressively. “D1.1 was initially found, I believe, in August of 2024 in the Pacific Flyway. It’s now in all four flyways, and so we know it’s in the environment, but this is the first time it’s been documented that D1.1 has been in a dairy cow,” said J.J. Goicoechea, director of the Nevada Department of Agriculture, was quoted by CNN.
He stated that the affected dairies have given the Nevada Department of Health contact information for their workers, who are being monitored for any signs of infection. Additionally, they are being provided with personal protective equipment. So far, no human cases have been reported in connection with the infected herds. Notably, the D1.1 infections in cows do not appear to be more severe than B3.13 infections, Goicoechea said.
Some symptoms to notice according to Goicoechea, are that cows would lose their appetite, and their milk production would drop.
Last year, bird flu spread across the country as infected cattle were shipped from Texas after the virus first leapt to cows from wild birds.
