The California Department of Food and Agriculture confirmed two weeks ago that a pair of commercial farms in Stanislaus County experienced highly pathogenic avian influenza outbreaks. The fast-spreading virus — also known as avian flu or bird flu — has forced the two farms to quarantine and euthanize their birds to prevent further spread of the disease.
The names of the two farms were not released, although the CDFA shared that they each raise an estimated 250,000 chickens.
The outbreaks in Stanislaus County came just four days after an outbreak was reported in Sonoma County and a week after the disease was detected in Fresno County.
In late October, Canada geese were found dead in Sacramento County and submitted to the California Department of Fish and Wildlife’s (CDFW) Wildlife Health Laboratory for testing. It was confirmed in November that they died from the Eurasian strain of Highly Pathogenic Avian Influenza (HPAI) H5N1.
Detections in waterfowl during hunter-harvest surveillance have been reported from Fresno, Glenn, Kern and Yolo counties.
This strain of Eurasian HPAI H5N1 has been circulating in the United States and Canada since the winter of 2021-22, arriving in California in mid-July 2022. In total, 354 confirmed detections of the virus were made in wild birds collected from 44 California counties during mortality surveillance conducted between July 2022 and June 2023. Detections of the virus appeared to subside during spring and summer in California, as well as more broadly in the United States. Now, as waterfowl and other water birds are undertaking fall migration, cases again are on the rise.
Like with humans, there is a flu season for birds, with some forms worse than others. The bird flu is found in some populations of wild waterfowl that can infect chickens, turkeys, pheasants, quail, ducks, geese and guinea fowl, as well as a wide variety of other domesticated and wild birds. Spread is normally caused by domestic bird-to-bird contact or through contact with contaminated people, feed or equipment once it is introduced into domestic avian populations.
According to the Centers for Disease Control and Prevention, the strain detected in Stanislaus County is considered of low risk to affect human health however, avian influenza is highly contagious and often fatal for birds.
The CDFA notes that, with the avian flu being widespread across California, it may also be present in other counties that are not yet flagged due to there being no laboratory submissions from the counties. The agency stressed that enhanced biosecurity is critical in the face of ongoing disease outbreaks, and urged farms to practice good avian biosecurity protocols.
Anyone may report any unusual or suspicious sick or dead domestic birds immediately through the CDFA Sick Bird Hotline at (866) 922-2473. Any unusual or suspicious wild bird deaths can also be reported online to the Department of Fish and Wildlife (CDFW) at www.wildlife.ca.gov/Conservation/Laboratories/Wildlife-Health/Monitoring/Mortality-Report.
