For the first time in the U.S., the highly pathogenic H5N1 bird flu virus was detected in swine, sparking concerns about how the virus may be spreading across species. Officials are investigating the case on an Oregon farm where the virus was found in a pig.

Out of five pigs tested on an Oregon farm, one tested positive for H5N1 bird flu, two tested negative, and results are pending for the remaining two.

"Although the swine did not display signs of illness, the Oregon Department of Health and USDA tested the five swine for H5N1 out of an abundance of caution and because of the presence of H5N1 in other animals on the premises. The swine were euthanized to facilitate additional diagnostic analysis," the U.S. Department of Agriculture said in a news release.

The livestock on the farm shared the same water, lived in shared or close housing, and likely had contact with the same equipment. As a precaution, officials are keeping the farm under quarantine and the other animals on the farm, including sheep and goats, under close surveillance.

Since the farm was not part of the commercial food supply, these findings do not raise concerns about the safety of the country's pork supply, the officials said.

"USDA's National Veterinary Services Laboratories (NVSL) has conducted genomic sequencing of virus from the poultry infected on this farm, and that sequencing has not identified any changes to the H5N1 virus that would suggest to USDA and CDC that it is more transmissible to humans, indicating that the current risk to the public remains low," the news release stated.

However, the transmission of the H5N1 virus to pigs is concerning since the pigs can become infected with bird and human viruses at the same time, which can result in a more dangerous mutated virus that can easily infect humans. Despite this, there is currently no evidence that the bird flu virus is mutating into more easily transmissible forms.

Last week, the Oregon Department of Agriculture reported that the virus was detected in a backyard flock, prompting the humane euthanizing of 70 birds. The location is now under quarantine.

The new finding should prompt pig farmers to be alert about infections, said Marie Culhane, a professor of veterinary population medicine at the University of Minnesota who has researched flu viruses in swine.

"People need to start increasing their plans to deal with it if it should happen in another herd. Pigs are just really good at picking up influenza viruses," Culhane said.

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