Avian flu likely circulated in a limited way among U.S. dairy cows for about four months before federal authorities confirmed the disease has now spread to nine states, according to a new federally funded research paper.
The U.S. Department of Agriculture reported the first H5N1 virus infection in a dairy cow in Texas on March 25, following reports of declining milk yields in several states.
The USDA said it believed wild birds, which can carry the virus, introduced H5N1 into livestock. The outbreak then spread when cows were shipped to other states, according to the paper published Wednesday and funded by the USDA, the Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases ( National Institute of Allergy and Infectious Diseases).
“The data confirm the existence of a single event of introduction of the virus of wild avian origin into livestock, likely followed by limited local circulation for approximately four months before confirmation by the USDA,” states the article.
A team of university scientists led by Michael Worobey, an evolutionary biologist at the University of Arizona, assembled the raw genetic sequences released by the USDA on April 21, without dates or locations, and concluded a week ago that Only one transmission event had occurred by the end of 2023.
Scientists have criticized the USDA for failing to release details of data that would allow university researchers around the world to trace the evolution of the virus.
One person, a Texas farmworker, tested positive for H5N1 in the current outbreak, although his only symptom was conjunctivitis, believed to have been caused by contact with cow’s milk. The CDC said the risk of infection to the general public was low.
Avian flu has long been on the list of viruses with pandemic potential, and any extension to a new species of mammal worries scientists.
Carol Cardona, a bird flu specialist at the University of Minnesota, said the virus may have spread during the four months it went undetected.
“When it was recognized, we were no longer able to contain the epidemic,” she said.
According to the article, veterinarians observed that dairy cows showed unexplained reductions in milk production and changes in milk quality, as well as reduced feed consumption, starting in January. It was published on an open access preprint server for the biological sciences called bioRxivon.
Members of the USDA network of disease-monitoring laboratories identified the influenza A virus, which includes avian flu, in milk and nasal swabs from cows at a Texas dairy, the article said. without specifying a date.
They forwarded samples to the USDA’s National Veterinary Services Laboratories, which respond to animal health emergencies, for testing while epidemiological investigations continued elsewhere, according to the newspaper.
The USDA did not immediately respond to a request for comment.
“Overall, it’s great that this data has been shared,” said virologist Angela Rasmussen of the Vaccine and Infectious Disease Organization at the University of Saskatchewan, who worked on sequencing the virus with Worobey. , in an article published on X. (Reporting by Tom Polansek and Julie Steenhuysen in Chicago; Editing by Cynthia Osterman).
