An avian flu outbreak, which killed several elephant seals at California’s Año Nuevo State Park last month, has spread to two other mammal species, according to researchers.
Laboratory testing confirmed the virus had spread to nine additional elephant seals, a southern sea otter and a sea lion, Christine Johnson, director of the Institute for Pandemic Insights at the UC Davis Weill School of Veterinary Medicine, and other wildlife specialists said during a media briefing on March 12.
UC Santa Cruz researcher in Hazmat suit taking nasal sample from elephant seal pup, Ano Nuevo State Park, California, USA
Scientists estimated that more than 60 marine mammals may have been infected by the virus and are currently being tested.
In total, scientists have confirmed that 16 elephant seals are infected with the HPAI H5N1 virus, commonly known as avian flu; however, Johnson noted that these numbers reflect only animals that have undergone rigorous testing.
“We know there are more animals with signs of infection that we have sampled that are being tested across the different laboratory systems,” Johnson said. “There are likely more animals that will be updated on in the coming weeks.”
Although all confirmed cases were found in mammals in San Mateo County, Año Nuevo State Park and Año Nuevo Island Reserve, Johnson noted that scientists have detected some cases “slightly to the south and to the north” of Año Nuevo, specifically in dead animals found on public beaches.
Ravens feeding on elephant seal carcass, Ano Nuevo State Park, California, USA
“It’s not at all unusual that this outbreak is impacting additional species, like we are seeing in the new cases with a sea otter and a sealion,” Johnson said. “H5N1 outbreaks affect a wide range of birds and mammals, and these animals all share the near-shore ecosystem. It is especially tragic when infections impact less-common species (like) the southern sea otter.”
Patrick Robinson, the Año Nuevo Reserve director at UC Santa Cruz, shared that scientists have found about 47 dead seals — both pups and adults, particularly males — along the shoreline since the outbreak began.
“Although some mortality of weaned pups are expected, this year’s mortality rate has been about four times higher compared to last year’s,” Robinson said. “The death rate in large males is basically nonexistent in most years. We don’t typically see large males passing away on beaches.”
UC Santa Cruz researchers in Hazmat suits heading towards elephant seal colony, Ano Nuevo State Park, California, USA
Robinson also noted that the mortality rate of elephant seals living on the Farallon Islands off the coast of San Francisco appears to be about “three times higher” compared to the deaths along the shore, based on drone surveys.
But in some good news, Robinson said the virus appears to be nonexistent among adult female elephant seals. About 80% of female seals had left the region as part of their foraging migration before the avian flu outbreak in mid-February.
“To date, no female elephant seals have been observed to be symptomatic or dead,” Robinson said.
The risk of the avian flu transmitting to the general public is very low, though the disease can spread between animals and people. Scientists recommend avoiding areas with infected animals, not touching live or dead seals, and not allowing pets to approach them.
If a person encounters a sick, injured or dead marine mammal in California, Oregon or Washington, they can call the NOAA Fisheries West Coast Region Stranding Hotline at (866) 767-6114.
Noe Padilla is a Northern California Reporter for USA Today. Contact him at npadilla@usatodayco.com, follow him on X @1NoePadilla or on Bluesky @noepadilla.bsky.social. Sign up for the TODAY Californian newsletter or follow us on Facebook at TODAY Californian.
This article originally appeared on USA TODAY: Bird flu outbreak in California park spreads to sea otter, sea lion
