Bird Flu Hits Over Half of California Dairies, Spurring More Containment Efforts

California agriculture and public health officials are taking steps to contain a rapidly spreading bird flu outbreak as the virus tears through the state’s dairies.

The spread was enough to prompt Gov. Gavin Newsom to declare a state of emergency this week, aiming to bolster the efforts of state and local officials to monitor the virus and keep it in check. The declaration will also help provide critical resources to affected communities, Newsom said.

“The emergency declaration allows us to expand our workforce to continue to monitor it closely and respond to the situation nimbly,” Dr. Erica Pan, California’s state epidemiologist, said at a briefing about the state’s response on Friday. “Helps us mitigate disease in animals, protect those at risk, and ensure we continue to learn about this bird flu virus.”

The proclamation follows infections rising among dairy cows in Southern California, which is concerning because the outbreak began elsewhere, in the Central Valley. The virus has been detected at 679 of the state’s 1,100-plus dairies, 51 commercial poultry farms and nine backyard flocks across the state, according to the California Department of Food and Agriculture (CDFA).

The virus is likely spreading between facilities via sick cows, equipment and trailers. CDFA is working with farmers to limit visitors from accessing their ranches, requiring workers to wear masks, gloves and other protective gear, as well as monitoring cattle for fevers, loss of appetite and other symptoms of bird flu. The agency is also testing the state’s 1.7 million cows weekly.

Agricultural officials do not expect the current outbreak to impact the milk supply from California, the nation’s leading milk producer.

Meanwhile, the U.S. Department of Agriculture continues to test the national milk supply for potential contamination. State officials have already issued recalls of raw milk linked to bird flu exposure. The founder of Fresno-based Raw Farm, the target of the recall, acknowledged that potentially contaminated milk may have reached up to 90,000 customers.

Experts have cautioned people against consuming milk products that are not pasteurized. Research shows the process effectively eliminates harmful pathogens.

She said the virus is a death sentence for poultry, which is why farmers usually euthanize birds that are exposed, said Dr. Annette M. Jones, state veterinarian and director of Animal Health and Food Safety Services. The symptoms are not as severe in cows, but the animals are stressed by the disease and may not recover completely.

“This is the third wave of [bird flu] infection since 2022 that our poultry flocks have experienced,” Jones said. “And the first time they have gotten a virus from cows.”

While human-to-human transmission has not been reported in California, public health officials are monitoring for signs that is happening. Most human cases in the state have been linked to people who were in direct contact with infected cattle.

California has recorded 36 human bird flu infections this year, underscoring the virus’s ability to jump from animals to humans. Nationwide, the U.S. has reported 61 cases in 2024, primarily among dairy and poultry workers.

Last month, a case in Alameda County involving a child with mild respiratory symptoms raised alarms when no clear exposure pathway was identified. The case, however, did not result in further spread within the family or school, aligning with trends seen in other human infections, which have generally caused mild symptoms such as conjunctivitis and nasal congestion. However, the confirmation this week of the first severe human case of bird flu in the U.S., reported in Louisiana, demonstrates that certain strains of the virus can lead to worse illness.

Wastewater surveillance has revealed the virus’ presence across the Bay Area, including in San Francisco, Napa and San José. Despite this widespread detection, health officials maintain that the risk to the general public remains low.