Avian flu likely circulated in dairy cows for at least four months before it was confirmed to be the highly pathogenic H5N1 virus, according to a new analysis of genomic data by scientists at the U.S. Department of Agriculture’s Animal Disease Center.
The investigation also found infected cattle with no apparent connection; this suggests that “there are affected herds that have not yet been identified.”
This adds to growing evidence showing that the H5N1 virus had a months-long head start in the U.S. dairy industry before attracting the attention of scientists and government regulators.
The USDA study was published as a preprint on the BioRXIV server on Wednesday, ahead of peer review.
This follows a similar analysis by an independent international group of nearly two dozen evolutionary and molecular biologists who quickly analyzed raw genome sequences uploaded by the government to a server maintained by the National Library of Medicine. Despite the lack of critical background information on these samples, this group came to almost the same conclusion as the USDA: The virus jumped from wild birds to cows between mid-November and mid-January, meaning the virus had been circulating for months before anyone knew it.
The USDA officially confirmed the presence of the H5N1 virus in dairy cows in Texas on March 25. At least three dozen infected swarms have since been reported in nine states. At least one farm worker in Texas who was in contact with infected cows also tested positive for H5N1; This was the second human case of this type of flu ever reported in the United States. The worker was given antiviral medication and recovered.
Tests of milk purchased from retail stores showed dormant traces of the virus in about 1 in 5 samples, suggesting the infection was widespread, according to a U.S. Food and Drug Administration report last week. Further testing by the FDA confirmed that the virus in samples of pasteurized dairy products was inactive and did not make anyone sick, but experts strongly recommended against the consumption of raw milk.
D., chair of the Department of Ecology and Evolutionary Biology at the University of Arizona, who was part of the group of biologists who conducted the independent analysis. “We could have done a much better job” catching H5N1 in dairy cows, Michael Worobey said. Worobey studies how pandemics begin.
Worobey said that once cows become visibly ill from a mysterious disease, instead of testing for specific viruses and bacteria, ideally a lab would use a technique called metagenomic sequencing, which reads all the genetic material in a sample and uses computer assistance. Select relevant information.
“If this had been done, H5N1 would have emerged in January or even later,” he said.
If we’re serious about preventing outbreaks in animals that could lead to outbreaks in humans, regulators need to change their approach, Worobey said.
“We need to get out of the mentality of waiting for sick animals or sick people to be the tip of the iceberg.” Instead, he said, animals should be routinely tested “with modern techniques” to identify emerging pathogens.
New study reveals how USDA bird flu spread so quickly through flocks across the United States. Samples collected between March 7 and April 8 found very similar H5N1 viruses in 26 flocks in eight states and six poultry flocks in three states; This suggests that the virus passed between wild birds and cows in a single spillover event.
The study says “production veterinarians” first noticed changes in milk production and quality from poorly fed cows in late January.
H5N1 has been decimating wild and domestic bird populations in the United States since 2022 and infecting increasing numbers of mammals.
In addition to movement between cattle and wild birds, the study found evidence that infected cattle transmitted the virus to domestic poultry flocks “via multiple routes of transmission.” Researchers also found that the virus involved in the current outbreak was transmitted to a wild animal (a raccoon) and cats living near cows on dairy farms.
Interestingly, the virus sequenced from the infected farmer had significant differences from the cow genomes. USDA scientists concluded that the differences may mean samples from animals the farmer had contact with were missing or could be due to evolution of the virus from host to host.
Worobey says the study means H5N1 “seems to have a seemingly well-established foothold in the country’s dairy cattle population” and could be something we’ll have to deal with for years to come.
Although it’s by no means clear that this virus would mutate into the right combination of pathways to start a pandemic in humans, allowing a virus to gain a foothold in a population of domesticated animals would put everyone at risk, he said.
“It adds another species that has not previously contained influenza A virus, which is a very important species, to the list of species where these viruses may have the opportunity to find the right combination that allows them to cause damage to the environment. “It’s not just animals, it’s also the human population,” he said.
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