California Declares an Emergency Over Bird Flu in Cattle

Officials have discovered the virus in 645 dairy herds, more than in any other state so far.

In a stark acknowledgment of the increasing seriousness of bird flu’s spread, Gov. Gavin Newsom of California declared on Wednesday that the outbreak of infections among the state’s dairy cattle constituted an emergency.

The announcement followed news earlier in the day that an individual in Louisiana had been hospitalized with bird flu, the first infected American to become severely ill.

The virus, H5N1, cannot yet spread easily among people, and it still poses little danger to the average American. Pasteurized dairy products are still safe to consume.

But the past few weeks have brought a steady drumbeat of cases in people, dairy cattle, birds and other animals. Each infection gives the virus a chance to take on a form that could cause a pandemic, experts warned.

“All these infections in so many species around us is paving a bigger and bigger runway for the virus to potentially evolve to infect humans better and transmit between humans,” said Dr. Nahid Bhadelia, the director of the Boston University Center on Emerging Infectious Diseases.

“That represents an escalation in the situation, even if risk to general population remains low,” she said.