H5N1 Bird Flu Confirmed in California Elephant Seals, Marking First Cases in Marine Mammals

The highly pathogenic avian influenza (HPAI) H5N1 virus, responsible for widespread outbreaks in birds and other animals globally, has been confirmed in northern elephant seal pups at Año Nuevo State Park in California. This marks the first detection of the virus in marine mammals in the state and the first cases ever identified in northern elephant seals, according to researchers from UC Davis and UC Santa Cruz.

First Detection and Rapid Response

Seven weaned elephant seal pups tested positive for the H5N1 virus, as confirmed by the U.S. Department of Agriculture’s National Veterinary Services Laboratory . Scientists noted the speed of detection was remarkable, attributing it to proactive surveillance efforts. “This is exceptionally rapid detection of an outbreak in free-ranging marine mammals,” said Professor Christine Johnson, director of the Institute for Pandemic Insights at the UC Davis’ Weill School of Veterinary Medicine .

Concerns and Prior Outbreaks

The outbreak raises concerns due to the devastating impact H5N1 has had on other elephant seal populations. In 2023, the virus decimated southern elephant seal populations in Argentina . Researchers are closely monitoring the situation, drawing on six decades of research on the Año Nuevo colony conducted by UC Santa Cruz .

Monitoring and Precautions

Researchers at UC Santa Cruz and UC Davis have been increasing disease surveillance in recent years due to concerns about the spread of avian influenza throughout North and South America . While most adult females had already begun their migrations before the outbreak, scientists are continuing to monitor the situation closely.

Authorities advise the public to maintain distance from seals, both living and deceased, and to retain pets away. Contact the NOAA Fisheries West Coast Region Stranding Hotline at (866) 767-6114 if you encounter a sick or dead marine mammal in California, Oregon, or Washington . Do not attempt to move sick animals, as this can spread the disease and cause further harm.

Ongoing Research and Collaboration

The scientific team is collaborating with NOAA Fisheries, the California Department of Fish and Wildlife, and the West Coast Marine Mammal Stranding Network to monitor marine mammals along the coast . UC Davis scientists have been testing samples from marine birds and mammals since 2024 , and the NSF Center for Pandemic Insights at UC Davis and UC Santa Cruz have been working together to increase surveillance at Año Nuevo State Park over the past two months .