Although many marine mammal deaths from avian flu are never reported, in 2023 we've seen literally tens of thousands of sea lions, seals, and other marine mammals killed by H5N1 (see Avian Flu's New Normal: When the Extraordinary Becomes Ordinary).
As recently as last Saturday, in NOAA Fisheries NWFSC: Three Harbor Seals In Puget Sound Test Positive For HPAI H5N1, we saw reports from our own Pacific Northwest.
Today we have this report from Denmark.
Outbreak of bird flu in seals
Highly pathogenic bird flu virus H5N1 detected in several seals that were recently found dead at Avnø.
Last edited on September 11, 2023
At the end of August, the emergency department for marine mammals was notified of the discovery of several dead seals at Avnø in South Zealand. The discovery was reported to the Pathology Unit at the University of Copenhagen, which is in charge of wild game surveillance.
"It is very unusual, so we went down to Avnø and took samples from the seals to clarify the cause of death if possible," says veterinarian Tim K. Jensen from the University of Copenhagen.
The seals were lying at the water's edge, and they are estimated to have died over a shorter period. Along with the seals, there were also a large number of dead mute swans on the beach. Most were just feathers and legs, so they must have been there for a long time. One of the swans was suitable for examination and was taken home to the institute for examination for avian influenza virus. There were clear signs of pneumonia in the seals that were suitable for autopsy, and subsequently highly pathogenic avian influenza H5N1 was detected in both the seals and the mute swan, which is considered to be the cause of death.
The studies were carried out in collaboration between the University of Copenhagen and the Statens Serum Institut, and further characterization of the virus is now underway, i.a. with a view to investigating whether it is the same virus in both the seals and the swan.
"Bird flu has since the end of 2020 caused great mortality among wild birds and has also affected herds with poultry and other birds in captivity in Denmark. A large number of countries in Europe as well as in Asia, Africa, North and South America are also affected", says senior researcher Charlotte Hjulsager from the Statens Serum Institut.
In rare cases, the bird flu virus can be transmitted to humans, so you should avoid direct contact with dead or sick wild animals. The general risk of infection to humans is assessed by the European Center for Disease Control (ECDC) to be low for the general population and low to moderate for people with occupational or other contact with infected animals and their surroundings.
In recent years, avian influenza has increasingly been detected in mammals, especially in wild predators and marine mammals, although it is still a rare phenomenon. It is especially dead or sick foxes and seals that have been found infected with bird flu.
"When bird flu viruses jump from birds to mammals, we have seen indications that viruses mutate so that they become better at infecting mammals," says professor of virology Lars E. Larsen from the University of Copenhagen. Highly pathogenic avian influenza has previously been detected in two harbor seals from 2021 and four foxes in 2022 in Denmark.
The Statens Serum Institut and the University of Copenhagen are monitoring the situation closely, and in collaboration with the Danish Food and Drug Administration, are monitoring avian influenza virus in Danish birds and mammals. Everyone can contribute by reporting finds of dead wild birds to the Danish Veterinary and Food Administration via the "Avian Influenza Tip" app. It is especially finds of dead birds of prey, and for other species, finds of many dead wild birds in the same place, that are relevant.
Findings of dead stranded marine mammals can be reported to the Preparedness for Marine Mammals telephone 76122000 or e-mail email@example.com". "Questions about the submission and examination of dead wild animals can be addressed to the fall wildlife monitoring (Patologivagten) on telephone 93509280 or e-mail firstname.lastname@example.org", says Anne Sofie Vedsted Hammer, veterinarian and associate professor at the University of Copenhagen.
Read more about finding dead wild birds with bird flu and precautions when finding dead wild animals on the Danish Veterinary and Food Administration's website
Reports like these are becoming all too common, and each spillover provides the virus with another opportunity to better adapt to mammals. Between wildlife infections like these, and the incursion of H5N1 into fur farms, and swine herds, the virus is getting a lot of help along its evolutionary path.
While it is still possible there is some, as-yet undefined, species barrier that protects us from HPAI H5 pandemics, the momentum right now is with the virus.
And no one really knows how this will play out.