Outbreak and Monitoring Overview
Initial outbreak investigation and H5N1 detection at Año Nuevo State Park
On 2/19/2026 and 2/20/2026, multiple northern elephant seal weanling pups (recently weaned from nursing) were observed dead at Año Nuevo State Park in San Mateo County, California. Live elephant seal weanlings were also observed with tremors and seizure activity. In collaboration with University of California, Davis, researchers from University of California, Santa Cruz responded to collect samples from 7 sick and dead animals for testing at the California Animal Health & Food Safety Laboratory System (CAHFS) laboratory at UC Davis. Initial screening revealed that the samples were positive for influenza A, subtype H5. The USDA National Veterinary Services Laboratory (NVSL) later confirmed infection with influenza A subtype H5N1 (Highly Pathogenic Avian Influenza, HPAI).
At this time, Año Nuevo had an elephant seal rookery with about 1,350 seals still on site, nearing the end of the breeding season. Scientists at the University of California, Davis have been screening seabirds and elephant seals at Año Nuevo State Park and other regions across the California coast since 2024. While dead seabirds have been detected with HPAI H5N1 at Año Nuevo State Park and other California locations in the winters of 2025 and 2026, this is the first detection in northern elephant seals or California marine mammals to date.
Sustained long-term collaborative monitoring
This outbreak was detected immediately due to the collaborative efforts of scientists at UC Davis and UC Santa Cruz who have increased disease surveillance of this population in recent years given concerns about the spread of HPAI. This elephant seal rookery has been closely monitored for decades by researchers at UC Santa Cruz including the Beltran Lab who are highly committed to long-term demographic observations of this population. Año Nuevo State Park does regular guided elephant seal tours for visitors, which are one of the highlights of the Park.
Together with UC Davis, research teams have monitored seals for signs of illness, screened dead seabirds and marine mammals, and ramped up surveillance once the virus was detected in seabirds earlier this winter. California has a robust stranding network that reports possible HPAI cases for testing at UC Davis and participates in the monitoring and collection of dead seabirds for testing, often the first indicator of a potential outbreak. Since the detection of this outbreak, scientists have been working closely with the National Oceanic and Atmospheric Administration (NOAA) Fisheries, California State Parks, California Department of Fish and Wildlife (CDFW), California Department of Public Health (CDPH), local health officials, The Marine Mammal Center (TMMC), the West Coast Marine Mammal Stranding Network, and other marine mammal researchers that monitor wild elephant seal populations.
Ongoing outbreak investigations activities
Research teams at UC Santa Cruz and UC Davis continue to intensively monitor the situation at Año Nuevo, including conducting regular drone flights and surveys to evaluate animal health, collect samples, and screen for HPAI activity in birds and mammals. Año Nuevo State Park has temporarily closed public access to elephant seal viewing areas and halted public tours for the season to protect the animals and minimize any potential for disease spread. Our priority is to safeguard the health of both animals and people. In addition, surveillance teams and the network of marine mammal responders are expanding investigations to neighboring areas and keeping an eye out for suspected new cases throughout the state.
Catalyzing innovation
The NSF Center for Pandemic Insights at UC Davis, with collaborators at 12 other institutions, including UC Santa Cruz and The Marine Mammal Center (TMMC), has been working to develop new technologies and methodologies to facilitate HPAI surveillance in populations that are less monitored and often harder to access. These include the use of drones, thermal cameras, and novel chemical sensors.
H5N1 Background
The detection of an outbreak of H5N1 in elephant seals in California is concerning because H5N1 strains have been linked to severe illness and widespread mortality in marine mammals in other regions of the world. The currently circulating strains of HPAI were detected in birds in North America in the early winter of 2021, and in seals in Maine in 2022. Since then, HPAI has spread to numerous wild birds, wild mammals, poultry flocks, and other livestock. The severity of infection in animals varies widely, from little or no illness to severe disease and death, depending on the host species and the specific viral strain. Throughout 2023, large die-offs in southern elephant seals, sea lions, and other marine mammals due to HPAI were detected in South America (overview here). There have been localized outbreaks of HPAI in marine mammals in the United States in Washington (2023), Maine (2022), and Florida (2022).
There have been 71 human cases in North America to date (02/22/2026), nearly all occurring in people with direct contact with infected livestock or poultry, and two of those cases have been fatal. More information on human cases can be found here.
Avoid contact with wildlife
People and their pets should avoid all contact with sick or dead wildlife. HPAI is a “zoonotic disease” that has the potential to spread between animals and people (and their pets). Although the risk of infection to the general public remains low, beachgoers should not touch live or dead seals or birds, or allow pets to approach seals or birds. They should maintain a safe distance of 150 feet. See the California Department of Public Health (CDPH) news release from 3/6/2026 here.
FAQs
- What is HPAI H5N1?
Avian influenza (a.k.a. “bird flu”) is a zoonotic disease that has the potential to spread between animals and people. However, the health risk posed by the current avian flu to the general public is low. Based on recent experiences in both North and South America, it is believed that the virus is most often transmitted from wild birds to seals (e.g. link) although there is evidence in South America for direct mammal-to-mammal transmission (e.g. link).
There are three main types of influenza viruses: A, B and C. Avian influenza A viruses, which include the virus that has been detected in this outbreak, are mostly carried by birds and can occasionally cross over the species barrier from birds to mammals. They cause clinical disease of varying severity and epidemics in people and other mammals, including seals. These are known as “zoonotic diseases,” meaning they have the potential to spread between animals and people. Both Influenza A and Influenza B viruses have been documented in seals in North America and Europe previously.
Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and the neuraminidase (N). There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes. Influenza A viruses can be further broken down into different strains. Learn more about flu viruses.- What can I do to help the investigation and the animals?
- The most important step members of the public can take to assist investigators is to immediately report any sightings of dead or distressed marine mammals. Do not approach or touch the animal and keep your pets far away. For sightings on the West Coast (CA, OR, WA) call the NOAA Fisheries West Coast Region Stranding Hotline: (866) 767-6114.
- Is this HPAI outbreak in seals associated with the larger outbreak in North America?
- The current outbreak of highly pathogenic avian influenza in North America was first detected in early winter 2021 in Newfoundland and Labrador, Canada. It has now been confirmed in nearly all U.S. states and Canada provinces, in commercial poultry, dairy cows, backyard flocks, many species of wild birds, and several species of terrestrial and marine mammals (including pets). More information can be found at USDA, NWHC, and CDC.
- What do I do if I find a sick or dead bird or mammal in California?
- Do not attempt to move sick wild animals to a veterinarian or rehabilitation center, or to your home, as this can spread the disease. Members of the public who find sick or dead animals should report them immediately. Birds should be reported here, marine mammals should be reported here. As feasible, authorized personnel may respond to remove carcasses and, if in an area or species where avian influenza has not been confirmed, test for the virus.
- What is the risk to humans from the avian influenza virus?
- Influenza A viruses especially have a relatively high rate of mutation, or change, which may allow them to cross species barriers and may cause severe disease in their new hosts. The Centers for Disease Control, the National Wildlife Health Center, National Institute of Health, state agencies, and other organizations like NOAA monitor events involving animal influenza viruses very closely. The public should take appropriate precautions for themselves and their pets. According to the CDC, the health risk posed to the general public is low; however, they recommend precautions. People and their pets should avoid all contact with sick or dead wildlife because HPAI can spread between animals and people (and their pets). Although the risk of infection to the general public remains low, beachgoers should not touch live or dead seals or allow pets to approach seals. They should maintain a safe distance of 150 feet or more away. And please respect closures and follow guidance at sites where special precautions are implemented.
- Are there any risks to pets?
- Yes. Dogs and cats also share infectious diseases with marine mammals. Cats are highly susceptible to HPAI H5N1 infections. They should not be allowed to approach live or dead marine mammals, birds or other wildlife or to sniff, consume or roll in dead marine mammals or birds or other wildlife or their parts. NOAA Fisheries recommends contacting your pet’s veterinarian to discuss the potential risk to pets in your local area, or if your pet bites or is bitten by a seal.
- What should I do to protect myself and my pets against these viruses?
- You should never approach or allow a pet to approach a live or dead marine mammal or seabird or other wildlife. Seals, like other marine mammals (dolphins, whales, and sea lions), are protected under the Marine Mammal Protection Act. People and their pets must maintain a safe distance (we recommend 150 feet) so as not to disturb the animal, which may be just resting on the beach, and to avoid injury to themselves, their pets, or the seals or other wildlife.
While marine mammals look cute, they are wild animals and can respond aggressively to threats and potentially transmit disease. Here are some safe viewing tips:
- Stay at least 150 feet away from seals or other marine mammals
- Keep dogs on a leash and don’t allow them to approach seals—seals and dogs can easily infect each other with diseases since they are closely related species
- Call NOAA Fisheries’ stranding hotline at (866) 767-6114 or a local marine mammal stranding network member if you detect a sick or dead seal or sea lion. - How do seals catch influenza A?
- While this is still an area of active investigation, most cases likely initiate from waterfowl or seabirds, which are the natural reservoirs for a diverse range of Influenza A variants and can be infected by HPAI with varying severity. Seals can be exposed by being close to birds through respiratory droplets or exposure to infected bird feces. Once a new variant of influenza has entered into a seal population, then there is potential for it to spread from seal to seal.
- How do influenza viruses affect seals?
- Sick animals may appear to have respiratory symptoms such as coughing or difficulty breathing, foam from mouth or nostrils, and may exhibit weakness, not respond to human presence, and/or abnormal behavior (such as tremors or convulsions or other involuntary movement) due to a brain infection. The organs most affected by HPAI H5N1 are the lungs and brain, though the infection is generalized across all body organs.
- What are the conservation implications for seals of this kind of outbreak?
- Some outbreaks are highly localized, and limited in both space and time while others are much more extensive. See this recent statement from the World Organisation for Animal Health regarding overall global impacts in wildlife.
- Who should I reach out to for more information?
- For media inquiries regarding how UC Davis is assisting with this outbreak, please contact Kat Kerlin at [email protected] or 530-750-9195.
For all other inquiries, visit the respective agency or institution page for contact details.