Particles of highly pathogenic avian influenza A were detected in tissue from a dairy cow, the U.S. Department of Agriculture (USDA) announced on May 24.
The influenza, also known as the bird flu or H5N1, was found in muscle and other samples from the cow, according to the USDA.
The cow was one of 109 sent to be culled “for systemic disease,” the agency said. Testing has been completed on 96 of the cows, and the cow is the only one to have viral particles.
Authorities are working to figure out where the cow came from and plan to work with its former owner.
Government personnel at the slaughterhouse “identified signs of illness in the positive animal during post-mortem inspection and prevented the animal from entering the food supply,” the USDA said. The meat did not enter the food supply, which should “provide further confidence that the food safety system we have in place is working,” according to the USDA.
The avian influenza jumped from birds to cattle in late 2023 or early this year, and has since infected at least 58 herds across nine states, according to the USDA. The states are Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota, and Texas.
Two humans in America have experienced confirmed cases of the flu: one in Michigan and one in Texas. Both people suffered eye inflammation and have since recovered, authorities say. Transmission from cows to the people is suspected.
Worldwide, a majority of nearly 900 patients reported to the World Health Organization since 2003 have died.
Officials stress that the current form of the virus has not been transmitting between people but that if the virus evolves it could spark a pandemic.
“Currently circulating A(H5N1) viruses do not have the ability to easily bind to receptors that are most prevalent in the human upper respiratory tract and therefore are not easily transmissible to and between humans,” U.S. Centers for Disease Control and Prevention researchers said on May 24. “However, because of the widespread global prevalence of A(H5N1) viruses in birds and other animals, continued sporadic human infections are anticipated. Further, if a novel influenza A virus acquires the ability to infect and be transmitted easily between persons in a sustained manner, an influenza pandemic could occur. Thus, investigation of every novel influenza A virus case in humans and comprehensive worldwide surveillance is critical to public health preparedness efforts.”
New Paper
In a new paper, meanwhile, researchers with the University of Wisconsin–Madison and other institutions said laboratory experiments on milk from cows infected with the bird flu found high levels of the virus in raw milk, even after five weeks.The researchers also tested different levels of pasteurization and found that heating the milk at 145 degrees for at least five minutes left the virus indetectable.
Virus was still detectable, however, in milk heated to 181 degrees for just 15 seconds. That temperature and time are similar to the flash pasteurization used by some dairy producers.
Disclosures included funding for other projects from the USDA and the U.S. National Institutes of Health (NIH). Limitations included the lab conditions.
The researchers also infected mice with samples of milk with bird flu. All the mice survived four days, when they were euthanized. High levels of virus were detected in respiratory organs, and moderate levels were found in some other organs.
“Collectively, our data indicate that HPAI A(H5N1) virus in untreated milk can infect susceptible animals that consume it,” the researchers said.
The study was funded by the National Institute of Allergy and Infectious Diseases, which is part of the NIH. The agency said that the findings “suggest that consumption of raw milk by animals poses a risk for H5N1 infection.”
