Cow photo via maxpixel.freegreatpicture.com

Cows at three dairies located in the Central Valley have tested positive for highly pathogenic avian influenza (HPAI), reported the California Department of Food and Agriculture last week.

When the herds began showing clinical signs consistent with HPAI on August 23-25, samples from these three sites were submitted to the California Animal Health and Food Safety  laboratory network for preliminary determination, then submitted to the National Veterinary Services Laboratory, where the test results were confirmed.

The locations of the dairies were not disclosed.

No human cases of HPAI have been confirmed in California related to this incident. The California Department of Health  will provide official confirmation of any human cases associated with this incident.

“We have been preparing for this eventuality since earlier this year when HPAI detections were confirmed at dairy farms in other states,” said CDFA Secretary Karen Ross. “Our extensive experience with HPAI in poultry has given us ample preparation and expertise to address this incident, with workers’ health and public health as our top priorities.”

According to CDPH and the Centers for Disease Control (CDC), this influenza virus is not considered a significant public health threat and the risk to humans is considered to be low. The primary concern is for dairy workers who come into close contact with infected dairy cows. The CDC has confirmed four human cases of HPAI in dairy workers in other states since April: one each in Texas and Colorado, and two in Michigan.

CDFA is working with public health officials and dairy owners to inform and monitor workers at the affected dairies in California, and to assist the dairies with providing personal protective equipment.

California’s supply of milk and dairy foods is safe and has not been impacted by these events, according to CDFA. As a precaution, and according to longstanding state and federal requirements, milk from sick cows is not permitted in the public milk supply. Also, pasteurization of milk is fully effective at inactivating the virus, so there is no cause for concern for consumers from milk or dairy products. Pasteurized milk and dairy items, as well as properly handled meat and eggs, continue to be safe to consume.

The HPAI virus has been detected in North American wild birds in the U.S. since 2022, with occasional transmission into domestic poultry or wild mammals in almost all states, including California. In March, the first US detection in cattle was confirmed in Texas, most likely due to a single spillover event from wild birds. Since that time, the USDA has linked new detections in cattle to the interstate and regional movement of infected or contaminated livestock, people, and equipment.

The affected dairies have been placed under quarantine on the authority of CDFA’s State Veterinarian, and enhanced biosecurity measures are in place. Sick cows are isolated and are being treated at the dairies; healthy cows have been cleared to continue shipping milk for pasteurization. Animal movement is being tracked and evaluated, as are other potential introduction pathways. Additional testing will be prioritized according to epidemiologic risk. CDFA’s preliminary investigation has confirmed that cows have been moved among these dairies recently. The investigation and response are ongoing.