By Leah Douglas and Tom Polansek, for Reuters
In December 2024 US authorities ordered a testing regimen for the nation's milk supply, amid increasing concerns over the H5N1 bird flu virus. Dairy cows in Ithaca, New York, on 11 December, 2024. Photo: AFP/ Michael M Santiago
- Second bird flu strain detected in dairy cattle for first time
- Detection came through US national milk testing program
- Containment is critical, veterinary expert says
US dairy cattle have tested positive for a strain of bird flu not previously seen in cows, the US Department of Agriculture says, ramping up concerns about the persistent spread of the virus.
The H5N1 virus has reduced milk output in cattle, pushed up egg prices by wiping out millions of hens, and infected nearly 70 people in the US since April, as it has spread across the country.
Genome sequencing of milk from Nevada identified the different strain, known as the D1.1 genotype, in dairy cows for the first time, the US Department of Agriculture (USDA).
Previously, all 957 bird flu infections among dairy herds reported since last March had been caused by another strain, the B3.13 genotype, according to the agency.
Reuters reported news of the detection of the second strain on Wednesday ahead of USDA's announcement.
The second strain was the predominant genotype among wild birds during America's last fall and winter, and has also been found in poultry, the USDA 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.
"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."
Wild birds likely transmitted the second strain to cattle in Nevada, said JJ Goicoechea, Nevada's agriculture director. Farmers need to ramp up safety and security measures to protect their animals, he said.
"We obviously aren't doing everything we can and everything we should or the virus wouldn't be getting in," he said.
The Nevada Department of Agriculture said on 31 January that herds in two counties had been placed under quarantine due to bird flu detections.
It is important for the USDA to contain the outbreak in the state quickly, so the strain does not spread to dairy cattle elsewhere, said Gail Hansen, a veterinary and public health consultant.
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.
"We didn't get a hold on it before," Hansen said. "We want to avoid that same scenario from happening in Nevada."
Dairy herds that were formerly infected may be at risk again from the second strain, experts said.
"Now it looks like we have new strains of virus that may escape some of the immunity associated with the other strains of viruses that could exacerbate the epidemics among animals and wildlife," said Gregory Gray, a University of Texas Medical Branch professor studying cattle diseases.
"It's alarming."
- Reuters
