H5N1 avian flu detected in a pig for the first time in the U.S.

For the first time, H5N1 bird flu has been found in a pig in the United States, according to a statement from the U.S. Department of Agriculture on Wednesday.

The USDA and Oregon veterinary authorities are investigating bird flu cases at a farm where poultry and livestock, including pigs, were kept together, the agency reported.

“The farm’s livestock and poultry shared water sources, housing, and equipment; in other regions, this has led to cross-species transmission,” the release explained.

After H5N1 was detected in other animals on the farm, five pigs were euthanized for testing; two returned negative results, while tests are still pending for the other two. The farm is now under quarantine, with additional animals being monitored. However, since this was not a commercial farm, the USDA’s Animal and Plant Health Inspection Service emphasized that there is no risk to the nation’s pork supply due to this discovery.

H5N1 is a rare strain of influenza in humans, but it is highly contagious and deadly in various animal species, including poultry and cattle. This raises concerns that it might mutate and become a virus capable of infecting humans.

Scientists have been worried about the possibility of H5N1 spreading to pigs, as they are considered a “mixing bowl” species for flu viruses, carrying similar receptors to those found in humans and birds. Past flu outbreaks in pigs, such as the 2009 H1N1 pandemic, are believed to have originated from a virus that mutated in pigs in Mexico before spreading to humans.

More than two dozen people in the United States have tested positive for H5N1 this year, with nearly all cases linked to exposure to infected dairy cows or chickens, according to the U.S. Centers for Disease Control and Prevention.

Some infectious disease experts have expressed a desire for more details regarding the Oregon pig case. Dr. Michael Osterholm questioned whether the virus was detected via a nasal swab or if there were signs of a more severe infection in the pig’s lungs.

“I believe they are jumping to conclusions by using the term ‘infection’ too quickly, as it could simply be environmental contamination on the pig’s nose. We need more data to confirm this,” said Osterholm, an expert in infectious diseases and director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

He pointed to a 2023 study where researchers attempted to infect pigs with H5N1 by swabbing their noses with the virus and feeding them contaminated food. The results were largely unsuccessful, with only one of eight pigs showing signs of the infection in their blood, indicating that the pigs had “high resistance” to the virus, according to the study authors.

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Osterholm expressed his approval of the ongoing studies on the animals involved in the current case, noting that additional research is necessary to gather more insights.

Veterinarians monitoring zoonotic infections said it’s not surprising that pigs on the same farm as infected birds might contract the virus.

“Virus sequencing will be crucial, but it's likely the bird strain circulating,” said Dr. Scott Weese, a veterinarian and infection control expert at the University of Guelph in Ontario, in an email to Dinogo. “My concern would be higher if it were dairy cows, as mammal-to-mammal transmission would be more alarming.”

“I believe this is a dead-end spillover, but it highlights the risks of cross-species contamination on farms,” Weese explained.

“These concerns would be more significant on larger commercial farms, where there’s a higher risk of pig-to-pig transmission and more opportunities for flu viruses to mix and exchange genes,” he added.