and spillover to mammals
#19,167
Although H5N1 remains the overwhelmingly dominant HPAI H5 subtype reported around the globe, we continue to follow other H5 subtypes bubbling up around the globe.
- Last February, in South Korea: H5N9 Rising, we looked at concerns over the arrival this past winter of a triad of HPAI H5 viruses in Korea; H5N1, H5N6, and H5N9.
- In Mexico, HPAI H5N2 has recently emerged, infecting both humans and poultry (Preprint: Emergence of a Novel Reassorted HPAI A(H5N2) Virus Associated with Severe Pneumonia in a Young Adult).
- Earlier this month China reported their 93rd human infection with HPAI H5N6, which has resulted in 58 deaths (62.4% CFR)
- In both Europe and in Eastern Canada, we've seen sporadic reports of HPAI H5N5 (see Cell Reports: Multiple Transatlantic Incursions of HPAI clade 2.3.4.4b A(H5N5) Virus into North America and Spillover to Mammals) since 2023.
- Additionally, HPAI H5N5 infected and killed a resident of Washington State last November, via contact with backyard birds.
While running a distant 2nd place to H5N1, H5N5 has shown surprising tenacity as it expands its geographic range, and reassorts with other LPAI viruses (see March 2026's Viral Creep: H5N5 Update)
In the summer of 2022, the Norwegian Veterinary Institute reported both H5N1 and H5N5 for the first time in wild birds on Svalbard, which lies above the Arctic circle (see More HPAI (H5N5 & H5N1) Detected In Arctic (Svalbard).
In the summer of 2022, the Norwegian Veterinary Institute reported both H5N1 and H5N5 for the first time in wild birds on Svalbard, which lies above the Arctic circle (see More HPAI (H5N5 & H5N1) Detected In Arctic (Svalbard).
Since then we've been tracking a small - but growing - number of spillovers of H5N5 to mammals in both Europe and Canada, including seals in the UK, domestic cats in Iceland, and raccoons (and other small mammals) in Canada.
Two summers ago (2024) in Cell Reports: Multiple Transatlantic Incursions of HPAI clade 2.3.4.4b A(H5N5) Virus into North America and Spillover to Mammals, researchers reported finding the mammalian adaptive E627K mutation in a number of samples.
While we typically see a drop in HPAI reports over the summer, it is because many of their avian hosts have migrated to their high latitude roosting spots - where they may find new opportunities to reassort and evolve - before returning next fall.
All of which brings us to a new report from the Norway Veterinary Institute, which describes the recent detection of HPAI H5N5 virus in both a dead walrus and a polar bear on Svalbard Island.
Although no other animals were confirmed infected during this investigation, there are eye witness accounts of two other polar bears exhibiting potential neurological symptoms.
I've reproduced the NVI statement below. Follow the link for additional photos and references.
(Translation)
First detection of avian influenza in polar bears in Svalbard
Published 19.05.2026
The Norwegian Veterinary Institute has detected avian influenza in a one-year-old male polar bear and an adult walrus in Raudfjorden north of Spitsbergen. This is the first time the virus has been detected in polar bears in Norway and Europe.Avian influenza virus was detected in a brain sample from the polar bear.
The detected avian influenza virus (HPAI) is of the subtype H5N5, a type of the virus that has also been previously detected in Svalbard: In wild birds in 2022, in a walrus in 2023 and in mountain foxes in 2025. This latest detection is the first in polar bears in Norway and Europe. *
Avian influenza viruses have also previously been detected in carnivorous mammals such as red foxes, otters and lynxes on mainland Norway after infection from wild birds.
Sampled in the field
In mid-May, the Norwegian Veterinary Institute was notified by the Norwegian Polar Institute of the discovery of a dead polar bear and a dead walrus in Raudfjorden on Svalbard. The animals were first observed by tourist guides. Two polar bears were also observed in the area showing lameness in their hind legs. This may be a neurological sign, which has previously been observed in polar bears infected with rabies and predators infected with highly pathogenic avian influenza.
"This gave us suspicion of a serious infectious disease, and two of us from the Veterinary Institute traveled to Svalbard to assist the Governor with sampling the dead animals in the field. With the help of a helicopter, the carcasses were quickly found and we were able to take samples. We observed no more sick polar bears from the air," says veterinarian and wildlife health specialist Knut Madslien.Walrus carcass on the shore in Svalbard. Despite the walrus being very rotten, it was still possible to detect the bird flu virus in the brain.
The samples were then sent to the Veterinary Institute and tested for avian influenza virus and rabies virus. Highly pathogenic avian influenza (HPAI) virus was detected in the samples from both the polar bear and the walrus. Rabies virus was not detected.
Bird flu virus is circulating in the highlands
"The findings are part of a trend where highly pathogenic avian influenza virus is increasingly being detected in mammals in Europe. At the same time, the virus has spread to new areas in recent years, including the Arctic, where it may have consequences for vulnerable populations and ecosystems," explains Ragnhild Tønnessen, avian influenza coordinator at the Norwegian Veterinary Institute.
“It is important to monitor the situation to understand developments and manage risk,” says Madslien.
Increased infection pressure in mammals
Most avian influenza viruses are best adapted to be transmitted between birds. However, mammals can sometimes be infected with avian influenza through direct contact with birds or other mammals infected with the virus, either sick or dead.
The Veterinary Institute will conduct further investigations of the detected virus to check whether it shows signs of being specifically adapted to mammals.
First detection in polar bears in Europe
In other predators, such as red foxes and lynxes, avian influenza can cause clinical signs of brain disease similar to those seen in rabies. Neurological signs such as circling gait, tilted head position, paralysis, and decreased shyness towards humans are common.
Avian influenza virus in polar bears has been scientifically published once before, in a young male polar bear found dead in Alaska in August 2023. It is not known how the virus affects individual individuals and the polar bear population.
Report if you observe dead or sick animals and birds
Both highly pathogenic avian influenza and rabies are serious diseases that can be transmitted to humans. Therefore, it is important to avoid contact with sick animals.
If avian influenza is suspected in birds and other animals on the mainland, the Norwegian Food Safety Authority must be notified . If sick or dead animals are observed in Svalbard, it is important that the findings are reported to the Governor .
The Norwegian Veterinary Institute is the national reference laboratory for avian influenza and has molecular methods for the detection and characterization of avian influenza viruses.
