Outbreaks of H5N1 bird flu in three California dairy herds located in the Central Valley have been confirmed by federal officials. The infections are believed to have resulted from interstate cattle transportation rather than exposure to infected wild birds, according to the LA Times.
Testing revealed that the virus strain in the California herds closely matches that found in Colorado dairy herds. The genetic sequence, identified as B3.13, strongly indicates human-facilitated movement of the virus between states.
While the California Department of Food and Agriculture (CDFA) reports no confirmed human cases of H5N1 in the state, four human infections linked to dairy have been reported in Texas, Colorado, and Michigan. Health officials consider the risk to humans low, with the primary concern being for dairy workers in close contact with infected cows.
The state’s milk supply remains unaffected, as contaminated milk is not permitted for sale, and pasteurization kills the virus. The CDFA said that the department had been preparing for this possibility since earlier in the year when bird flu was detected in dairy farms in other states.
To curb the spread of the virus, the U.S. Department of Agriculture (USDA) implemented restrictions on interstate cattle transfers in April. These measures include mandatory testing of lactating dairy cattle before transfer and reporting of positive cases prior to interstate movement.
The dairy industry’s practice of large-scale cattle movement, including sending calves to specialized rearing farms, has been identified as a potential factor in the virus’s spread. Research from Texas Tech University in 2022 found that 1 in 10 dairy-born calves were raised off-site, increasing to nearly 5 in 10 for farms with over 500 lactating cows.
According to the USDA, 197 herds across 14 states have been impacted since the virus was first detected in U.S. dairy cattle in March. California officials have quarantined the three infected herds, with all animal movement now requiring permits and adherence to strict biosecurity protocols.
The locations of the affected herds have not been disclosed due to privacy concerns. State and federal agencies are working closely with dairy farmers to monitor for signs of infection and implement best practices to contain the outbreak.
Food Poisoning News last wrote about bird flu in April. The U.S. Food and Drug Adminstration (FDA) confirmed that the nation’s milk supply was safe because of both pasteurization and the destruction of milk from sick cows.
Commenting on this story, one national food poisoning lawyer said, “Federal oversight is crucial to ensure the safety and integrity of our food supply. It is critical to both protect public health and maintain consumer confidence.”
