SALEM — Nearly 800,000 birds at two commercial poultry operations have been euthanized in the wake of the latest avian flu outbreak in Oregon, the state Department of Agriculture reports.

This is the largest outbreak of highly pathogenic avian influenza in the state, according to ODA statistics.

The two commercial poultry operations impacted are in Linn and Marion counties in the Willamette Valley. Two backyard operations in Marion and Deschutes counties were also impacted, according to ODA.

The Linn County business had 675,000 infected chickens, and the Marion County company had 123,500, USDA data shows.

The USDA’s National Veterinary Services Laboratory recently confirmed the presence of highly pathogenic avian influenza in the four flocks. There is no cure or vaccine for HPAI.

Dr. Ryan Scholz, the state veterinarian, has quarantined the commercial operations to prevent the transportation of poultry or poultry products to or from them, according to an ODA news release.

According to USDA updated figures on Nov. 20, 47 states have been affected by HPAI and 63.7 million birds nationwide have been euthanized.

Avian influenza does not affect poultry meat or egg products, which remain safe. HPAI is also considered low risk to human health, according to the U.S. Centers for Disease Control.

According to the World Health Organization, the avian flu outbreaks pose ongoing risk to humans as the virus has infected mammals more closely linked to people than birds.

The risk to mammals appeared linked to the scavenging of carcasses of wild birds that have died of HPAI, according to ODA.

HPAI has been detected in 32 backyard Oregon flocks, according to the USDA. Almost any and every poultry species imaginable has been infected since May 5, 2022, Scholz said.

Instances of infection were in Union, Klamath, Umatilla, Polk, Douglas, Josephine, Columbia, Yamhill, Tillamook, Coos and Lane counties.

All previous detections in Oregon were in backyard flocks, according to ODA.

These are the first avian influenza cases at commercial poultry facilities in Oregon, Scholz said.

“We don’t know why it happened. Sometimes it’s just a random, chance event. Most farms have strong biosecurity plans. We haven’t been focused too much on that piece yet. That will come. We’ve been focused on stopping the spread,” Scholz said.

Oregon’s cases are tied to a global outbreak of avian influenza that has been spreading for nearly two years and are a symptom of what’s happening with the nation’s wild waterfowl population.

“Lots of wild ducks and geese migrating through the state are carrying the virus,” Scholz said.

“This could happen any time domestic poultry are exposed to wild waterfowl, which is why biosecurity becomes so important,” he added.

Most western states have previously had commercial positives, and Oregon’s number of birds euthanized isn’t the top figure in the country this week, Scholz said.

There have been 371 commercial flocks and 558 backyard flocks throughout the United States that have had infections during the outbreak as of Nov. 20, according to USDA data.

Oregon has had roughly 800,500 birds euthanized during the outbreak.

Washington has had one commercial flock and 43 backyard flocks infected, with avian influenza in nearly 1.02 million birds.

California has had 17 commercial flocks and 20 backyard flocks impacted, with 836,000 birds euthanized.

Idaho has had one commercial flock and 32 backyard flocks infected, affecting 10,300 birds.

In one Oregon case, a hunter unknowingly brought an infected goose back to his home, exposing chickens on the property to the virus.

Residents could bring avian influenza back to their properties on hip waders or on shoes they wear at parks if they walk through duck or goose poop, Scholz said.

“Wash your hands, clean your boots. It makes a big difference. It can almost always be prevented with some basic steps,” Scholz said.

Biosecurity measures, he added, are why Oregon lasted this long through the national outbreak without a commercial positive.

This story has been updated.