A highly lethal strain of avian influenza has been confirmed in US dairy cows in Texas and Kansas. Department of Agriculture announced on Monday.
This is the first time that infected cows have been identified.
Cows appear to be infected by wild birds, and some farms have reported dead birds, the agency said. The results were announced after several federal and state agencies began investigating reports of sick cows in Texas, Kansas and New Mexico.
The disease primarily affects older cows, causing loss of appetite, fever and a sudden drop in milk production. So far, the USDA said, there have been few or no deaths in affected herds.
In several cases, the virus was detected in unpasteurized samples of milk collected from sick cows. Experts said pasteurization was supposed to inactivate the flu virus, and officials insisted the milk supply was safe.
“At this point, there are no concerns about the safety of the commercial milk supply or that this situation poses a risk to consumer health,” the company said in a statement.
Outside experts agreed. “It's only been detected in very unusual milk,” said Dr. Jim Lowe, a veterinarian and influenza researcher at the College of Veterinary Medicine at the University of Illinois at Urbana-Champaign.
In those cases, the milk was described as thick and syrupy and discarded. The agency said it requires dairies to divert or destroy milk from sick animals.
The livestock outbreaks have come with the country's first detection of highly pathogenic avian influenza in goats. Minnesota officials announced last week.
So far, flu samples from sick cows do not contain genetic mutations that make the virus known to be more likely to infect humans, making the risk to the general public low, the agriculture agency said.
Stacey L., a virologist and influenza specialist at St. Jude Children's Research Hospital. Schultz-Cherry said. “It looks like another spillover event due to contact with sick wild birds.”
However, he noted, cows are not considered one of the species particularly susceptible to bird flu, and the cases are another worrying twist in the global bird flu outbreak that has decimated wild bird populations over the past few years.
The outbreak was caused by a new strain of bird flu virus known as H5N1 that emerged in Europe in 2020. Wild birds can transmit the virus to farmed poultry and other animals through their feces and oral secretions. Infections often flare up in the spring and summer when migratory birds move.
Although avian influenza viruses are primarily adapted for transmission among birds, the new version of H5N1 has become so widespread in wild birds that it has repeatedly spread to mammals, especially scavenger species such as foxes, which may feed on infected birds.
Mammalian infections provide new opportunities for the virus to evolve, which is always a cause for concern, said Andrew Bowman, a molecular epidemiologist and influenza expert at Ohio State University. Scientists have long worried that an avian flu virus that has evolved to spread more efficiently among mammals, including humans, could trigger the next pandemic.
At this point, Dr. Bowman said, it's not clear whether all the infected cows picked up the virus directly from the birds or whether the virus was spread from cow to cow.
“This is a question that needs to be resolved soon,” he said. “If we have cattle-to-cattle transmission, that's a different story. That definitely makes me a little more nervous.
Additional testing and analysis is ongoing. “This is a rapidly evolving situation, and USDA and federal and state partners will share additional updates as information becomes available,” the agency said.
