#16,897
We've known for decades that marine mammals (seals, whales, sea lions, otters, etc.) are susceptible avian, and other types, of influenza viruses.
- During the winter of 1979-1980 seals were found suffering from pneumonia on the Cape Cod. In that instance, the culprit turned out to be an H7N7 influenza. (see Isolation of an influenza A virus from seals G. Lang, A. Gagnon and J. R. Geraci)
- In 1984 influenza subtype H4N5 – a strain previously only seen in birds – was determined to be behind the deaths of a number of New England seals in 1982 and 1983 (cite Are seals frequently infected with avian influenza viruses? R G Webster et al.)
- In the mid-1980s 2 flu viruses (H13N2 and H13N9 subtypes) were isolated from Pilot Whales (cite Characterization of two influenza A viruses from a pilot whale R G Webster et al.)
- And in 1995, in the Journal of General Virology, authors R. J. Callan, G. Early, H. Kida and V. S. Hinshaw wrote of the The appearance of H3 influenza viruses in seals during the early 1990s.
- Seals have also been shown susceptible to influenza B (cite Influenza B virus in seals. Osterhaus AD, Fouchier , et al.).
But over the past decade - as avian influenza has increased it geographic range - we've seen an increasing number of seal die offs from the virus.
- In November of 2011 a die off of seals in New England that was eventually tied to an H3N8 avian Flu Virus. 2012's mBio: A Mammalian Adapted H3N8 In Seals, presented evidence that this virus had recently adapted to better bind to alpha 2,6 receptor cells, the type found in the human upper respiratory tract.
- In 2013 a report (and a study) from UC Davis showed the human 2009 pandemic H1N1 virus had jumped to wild California Elephant Seals just one year after that virus emerged (see The 2009 H1N1 Virus Expands Its Host Range (Again)).
- In 2017, during the HPAI H5N8 epizootic in Europe, that emerging subtype (clade 2.3.4.4.B) was found in Grey seals in the Baltic Sea (see EID Journal: Highly Pathogenic Avian Influenza A(H5N8) Virus in Gray Seals, Baltic Sea).
- The biggest incident in recent memory, however, came in northern Europe (mostly Denmark and Germany & Sweden) in 2014, when as many as 3,000 harbor seals reportedly died from avian H10N7 (see Avian H10N7 Linked To Dead European Seals), prompting warnings to the public not to touch seals.
- In 2017, during the HPAI H5N8 epizootic in Europe, that emerging subtype (clade 2.3.4.4.B) was found in Grey seals in the Baltic Sea (see EID Journal: Highly Pathogenic Avian Influenza A(H5N8) Virus in Gray Seals, Baltic Sea).
- Reports continued into 2021 (see Two Reports On HPAI H5N8 Infecting Marine Mammals (Denmark & Germany and H5N1 in seals in Sweden and the UK).
This year, we are seeing multiple reports of seal die-offs attributed to avian H5Nx, both here in North America (New England & Canada), and in Europe (UK, Denmark & Germany), along with numerous other reports of spillovers into terrestrial mammals (see here, here, here, and here).
Quebec: Seal Deaths Linked To Avian H5N1
Maine: Seal Deaths Linked To Avian H5N1
Two Reports On HPAI H5N8 Infecting Marine Mammals (Denmark & Germany)
The most recent update from NOAA Fisheries on seal deaths in New England (see below) shows that unusual mortality event continues.
2022 Pinniped Unusual Mortality Event along the Maine Coast
Since June 2022, elevated numbers of harbor seal and gray seal mortalities have occurred across the southern and central coast of Maine. This event has been declared an unusual mortality event (UME).
Since June 2022, elevated numbers of sick and dead harbor seal (Phoca vitulina) and gray seal (Halichoerus grypus) have been documented along the southern and central coast of Maine from Biddeford to Boothbay (including Cumberland, Lincoln, Knox, Sagadahoc and York Counties). This event has been declared an Unusual Mortality Event (UME).
Why are Seals Stranding?
Preliminary testing of samples has found some harbor and gray seals positive for highly pathogenic avian influenza (HPAI) H5N1. There is an ongoing HPAI H5N1 event North America that was first detected in early winter 2021. The first detections in Maine waterfowl were in February 2022. HPAI H5N1 has now been confirmed in 41 U.S. states and 11 Canada provinces, in commercial poultry, backyard flocks, nearly 90 species of wild birds, eight species of scavenging mammals, and now seals. NOAA Fisheries is working with our local, state, tribal, federal and international partners in the investigation of HPAI in seals. HPAI is a “zoonotic disease” that has the potential to spread between animals and people (and their pets).
While the risk to the public is considered low, avian H5N1 has demonstrated a limited ability to infect humans, and so we are seeing warnings from both sides of the pond (see CDC: A Reminder About Pets and Avian Flu) to avoid contact with sick or dead (marine or terrestrial) animals.
The health risk posed by avian flu to the general public is low; however, precautions are recommended. Please do not touch live or dead seals, don’t allow pets to approach the seal, and observe the animal from a safe distance of 150 feet (safe for you and the animal).
All of this increased activity, and prospects that H5Nx may become a more frequent visitor, have lead the UK's Human Animal Infections and Risk Surveillance group (HAIRS), to issue a risk assessment (below) on avian influenza in local seal populations.
As you will see, while this HAIRS report describes both the risk, and impact, of exposure to infected seals to be VERY LOW to LOW, it goes on to describe their confidence (based on limited data) of their assessment as Poor/Satisfactory.
First the link, and description of the report, followed by some excerpts. You will probably want, however, to follow the link and read it in its entirety:
Influenza of avian origin in UK seal populations: qualitative assessment of the risk to the UK human population
Published 19 July 2022
Details
Avian influenza viruses (AIV) have long been recognised in Europe where there is longstanding annual surveillance for poultry and wild bird infections. Whilst there is no routine surveillance for diseases including AIV specifically in marine mammals in the UK, sporadic findings of AIV infecting seals have been reported. These include subtypes A(H3N8) isolated from a juvenile grey seal in 2017, and A(H5N8) from a grey seal and 2 common seals (or harbour seal) in 2020.
Although the UK is home to 38% of the entire world’s population of grey seals and 30% of the European subspecies of common seals, there have never been reports of AIV transmitting from seals to humans, or vice versa, in the UK.
As the number of incidents involving AIV infections in terrestrial and marine mammals has increased, including in seal populations, this has warranted an assessment of the risk AIV in UK seal populations pose to people with whom they may come into contact.
(Excerpt)
Probability
General population: very low.
The probability of infection would be considered low for those working with infected seals.
Impact
Very low to low.
Level of confidence in assessment of risk
Poor/Satisfactory.
AIV outbreaks in seal populations have occurred sporadically over time. Due to the absence of routine disease surveillance in UK seal populations, the true extent of AIV infections in seal populations cannot be determined. There is a paucity of evidence on the susceptibility of humans to AIV’s infecting seals, and only 2 documented incidents of AIV transmission from seals to humans, both resulting in mild disease in human cases. Several questions relating to the viral ecology and adaptation to marine mammal hosts exist. Other evidence gaps include:
Actions and recommendations
- How does viral genetic diversity, particularly in recovering seal populations or subpopulations, impact disease maintenance and viral circulation?
- Are small host populations more highly impacted by disease events, even in the absence of high mortality?
- Do genetic differences between marine mammal hosts (for example seal species) impact the ecological role of those hosts in virus maintenance and circulation?
- Do marine mammal-adapted viruses share molecular signatures of other mammalian adapted viruses?
During April 2021, an information campaign was launched by the Seal Alliance and Defra to educate the public on keeping their distance from seals to protect human and seal health. The general public are advised against approaching and interacting with seals in the UK, even when the animals are in danger or distress.
If a member of the public observes a seal they deem in danger or distress, they should contact an appropriate helpline for advice and assistance (for example the RSPCA in England and Wales, the SSPCA hotline in Scotland and the USPCA in Northern Ireland).
Individuals who come into close contact with seals as part of their work should consider utilising appropriate personal protective equipment (PPE) including aerosol-related respiratory precautions, and seal-specific precautions such as thick gloves and wooden boards or barriers if direct contact with a seal is necessary (for example during a seal rescue), to avoid animal bites and reduce the exposure to potential zoonotic infections.
The APHA wildlife expert group maintains close interactions with non-governmental organisations (NGOs) including marine wildlife organisations and rescue centres. Where appropriate, NGOs should be encouraged to collect and submit samples from sick or dead seals to APHA Weybridge diagnostic laboratories for testing, of which AIV should be a considered differential, so to be alerted to changes in viral epidemiology and potential risk.
A review of seal health surveillance across the UK is recommended, with the long-term aim to establish routine disease surveillance in marine mammals in the UK.
Please note: this risk assessment provides an ecological perspective on AIV in seal populations globally and reviews the probability of AI exposure from infected seals to humans in the UK. The statement provides reference to multiple AIV subtypes that have been reported to infect marine mammals, including seals. It does not assess, in detail, the risk of individual AIV subtypes to human health, but more so on the potential transmission pathway of AIV from seals to humans. Existing risk assessments for specific AIV subtypes can be found at Avian influenza: guidance, data and analysis.
For those interested, the `2 documented incidents of AIV transmission from seals to humans' referred to in the above report come from a 1981 NEJM report called Conjunctivitis in Human Beings Caused by Influenza A Virus of Seals, and the avian subtype involved was H7N7.
You can find additional information in the 1991 Virology report Characterization of an influenza A virus from seals R G Webster et al.
While the risks currently appear low - over time, should these viruses become better adapted to mammalian hosts - those assessments may need to be changed.
