The U.S. Department of Agriculture (USDA) has identified a novel strain of H5N1 avian influenza in dairy cattle, marking the first documented occurrence of this genotype in bovines, according to the agency's Animal and Plant Health Inspection Service.
Before this detection, all 957 confirmed cases of H5N1 in dairy cattle reported this year had been caused by the same viral strain, according to USDA data.
The CDC has reported nearly 70 human cases of H5N1 avian influenza in the U.S. since April, primarily among farm workers with direct exposure to infected livestock.
The USDA's genomic analysis of milk samples from Nevada confirmed the presence of a genetically distinct H5N1 strain in dairy cattle for the first time. Reuters reported the detection of the second strain on Wednesday ahead of the agency's announcement.
That second strain was the predominant genotype among wild birds this past fall and winter, the agency said. It was identified through the USDA’s National Milk Testing Strategy, which began testing milk across the country for H5N1 in December.
On January 31, the Nevada Department of Agriculture reported that dairy herds in two counties were placed under quarantine following H5N1 detections. The specific strain was not disclosed, though it had been previously identified in wild birds. The state agency did not immediately respond to a request for comment.
The USDA on January 31 reported four dairy herds in Nevada with confirmed H5N1 infections, according to agency data.
Containment is critical to preventing further spread, said Gail Hansen, a veterinary and public health consultant. Last year, the virus spread across the country as infected cattle were transported from Texas after the virus first leapt to cows from wild birds.
“Previous outbreaks were not contained before infected cattle were transported across state lines, facilitating viral dissemination,” Hansen said. “We want to avoid that same scenario from happening in Nevada.”
The USDA requires lactating dairy cattle to be tested for H5N1 before crossing state lines.
“My suspicion is that cattle that had been infected with the earlier strain are not necessarily going to be protected against this strain,” Hansen added.
