Cows at three California dairies located in the Central Valley have tested positive for highly pathogenic avian influenza (HPAI), according to the California Department of Food and Agriculture. These are the first cases of avian flu in cattle for the state.

When herds began showing clinical signs consistent with HPAI on August 25, 2024, the dairy owners worked with their veterinarians and the CDFA to submit samples to the California Animal Health and Food Safety (CAHFS) laboratory network for preliminary determination. The samples were then submitted to the National Veterinary Services Laboratory (NVSL), where the test results were confirmed.

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; and 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.

No human cases of HPAI have been confirmed in California related to this incident.

“We have been preparing for this possibility 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. This is a tough time for our dairy farmers given the economic challenges they’re facing in a dynamic market, so I want to assure them that we are approaching this incident with the utmost urgency.”

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 low. The primary concern is for dairy workers who come into close contact with infected dairy cows. CDPH recommends that PPE (masks, gloves, caps, face shields, and safety goggles) be worn by farm workers and emergency responders when working with animals or materials that are infected or potentially infected with avian influenza.

Earlier this summer, CDPH supported a one-time distribution of protective equipment for dairy farm workers and others handling raw dairy products, as well as for slaughterhouse and commercial poultry farmworkers. CDPH will continue to support dairies with confirmed positive cases with PPE. Furthermore, affected farms can take advantage of a USDA grant that provides financial support for producers that supply PPE to employees. CDFA is working with public health officials and dairy owners to inform and monitor workers at affected dairies in California, and to assist the dairies with education and resources to protect their workers, including providing PPE.

CDFA also noted that California’s supply of milk and dairy foods is safe and has not been impacted by these events.

No California domestic poultry flocks are affected by the current incident.

Michigan, New Mexico report new cases

USDA’s Animal and Plant Health Inspection Service confirmed last week that one dairy herd in Michigan as well as one dairy herd in New Mexico have tested positive for the virus. The New Mexico case is the first since April for the state.

Since late March, a total of 197 cases of HPAI have been confirmed in dairy herds in 14 states.