In the last 30 days, seven commercial poultry operations in California have been confirmed with highly pathogenic avian influenza (HPAI), five of which have been in the last week. According to USDA’s Animal and Plant Health Inspection Service (APHIS), approximately 1.57 million birds have been affected in California during the 30-day period.

Three commercial broiler operations were depopulated in Kings County while another was depopulated in Fresno County. In Sacramento County, a commercial turkey operation of 48,300 birds was the latest poultry operation to report the virus.

“The source of infection in these flocks is currently unknown and under investigation. Testing of other farms in the area will be conducted over the next several weeks to determine the extent of spread,” the California Department of Food and Agriculture (CDFA) stated in an Oct. 30 update. “We strongly urge all poultry owners in California to protect their flocks by increasing their biosecurity practices.” 

According to CDFA, clinical signs of HPAI include sudden death, trouble breathing, clear runny discharge (from nose, mouth, and eyes), lethargy, decreased food and water intake, swelling (eyes, head, wattles, or combs), discolored or bruised comb, wattles, or legs, stumbling/falling, or a twisted neck.

The state has also been a hotbed for the virus in dairy farms, logging 150 dairy herds with the virus over the past 30 days.

USDA builds on actions

APHIS recently announced last week that it is planning to enhance testing and monitoring for H5N1, building on measures taken by USDA since the beginning of the avian influenza outbreak. In partnership with state veterinarians, USDA said will implement a tiered strategy to collect milk samples to better assess where H5N1 is present, with the goal to better inform biosecurity and containment measures, as well as to inform state-led efforts to reduce risk to farm workers who may be in contact with animals infected with H5N1. 

Since this disease was first detected in dairy cattle in March 2024, the USDA and state and federal partners have taken several steps to better understand the virus in order to eliminate it from dairy herds. In May 2024, USDA implemented a Federal Order to require the testing of cattle before interstate movement, which has helped to limit H5N1’s spread to new states; in the past 30 days, the number of states with known avian influenza detections in dairy herds has dropped from 14 to two. However, USDA believes that additional steps are needed to proactively support effective biosecurity measures.

USDA has precedent with successful bulk milk testing approaches, including the use of bulk milk testing to eradicate brucellosis from dairy herds. In addition, Colorado implemented statewide bulk milk testing after H5N1 was detected in dairy herds in two counties, and the most recent statewide testing has not detected any evidence of H5N1 in any herds in the state. In the coming weeks, USDA will work with regions and states that are ready to assist in expanding bulk milk testing.  

The plan is to first sample milk in bulk at the regional level, with additional testing at the farm level, if necessary, until herds in an area are determined to be free of the virus. The agency said it will continue to work with state and private veterinarians on the final details of implementation and will share guidance documents soon. 

In the meantime, biosecurity remains the best weapon against the spread of H5N1, and farms should practice good biosecurity even if the virus has not been detected in their state or vicinity, USDA said. “Data collected over the past seven months has shown that H5N1 can be transmitted on equipment, people, or other items that move from farm to farm, including between dairies and poultry facilities.”

USDA continues to support the rapid development and timely approval of an H5N1 vaccine for dairy cows, in addition to other species. Two vaccine candidates for use in dairy cows are currently undergoing field trials.