First cases of deadly avian flu detected among California elephant seals
By Carlos E. Castañeda
Multiple elephant seal pups along the Northern California coast have tested positive for the deadly avian influenza, or bird flu, according to new research from the University of California.
Researchers from UC Davis and UC Santa Cruz collected samples from seven elephant seal weanling pups found dead last week at Año Nuevo State Park in San Mateo County, and also observed live weanlings with tremors and seizure activity, according to a press release on Wednesday.
Testing at the California Animal Health & Food Safety lab at UC Davis showed the samples were positive for the highly pathogenic avian influenza (HPAI) subtype H5N1. The findings were confirmed Tuesday evening by the U.S. Department of Agriculture’s National Veterinary Services Laboratory.
UC Davis said its scientists and researchers at UC Santa Cruz’s Beltran Lab have been screening seabirds and elephant seals at Año Nuevo State Park and other areas along the California coast, and have previously detected multiple seabirds with HPAI H5N1.
“This is exceptionally rapid detection of an outbreak in free-ranging marine mammals,” said Professor Christine Johnson, director of the UC Davis Institute for Pandemic Insights, in a prepared statement. “We have most likely identified the very first cases here because of coordinated teams that have been on high alert with active surveillance for this disease for some time.”
The researchers said that this outbreak is the first among marine mammals in California and the first detection in northern elephant seals, which range across the eastern and central North Pacific Ocean from Alaska to Baja California, Mexico. A similar outbreak decimated the population of southern elephant seals in Argentina in 2023.
H5N1 strains have been linked to severe illness and widespread mortality in marine mammals in other parts of the world. First discovered in 1996 in Southeast China on a domestic goose farm, strains were found in birds in North America in 2021, and in seals in Maine in 2022, researchers said. It has since spread to other wild birds, mammals, poultry flocks, and other livestock, with localized outbreaks of HPAI in marine mammals in Washington, Maine, and Florida.
The U.S. Centers for Disease Control and Prevention says there have been 71 human cases of bird flu in North America as of February 2026, with 38 of those in California. Nearly all the cases involved people in direct contact with infected livestock or poultry, the CDC said. Two of those people have died.
Researchers said their group was working with the National Oceanic and Atmospheric Administration, the California Department of Fish and Wildlife, and the West Coast Marine Mammal Stranding Network to continue monitoring marine mammals along the coast.
Health experts say that while the risk of infection to the general public is very low, bird flu can spread between animals and humans. People are advised not to touch live or dead seals or allow pets to approach them.
Anyone who encounters a sick, injured or dead marine mammal is asked to call the NOAA Fisheries West Coast Region stranding hotline at (866) 767-6114.
