Avian Flu Diary: Quebec: Seal Deaths Linked To Avian H5N1

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A little over a week ago, in Maine: Seal Deaths Linked To Avian H5N1, we looked at the ongoing unusual mortality event occurring along the rocky shores of Maine (see chart below), which has been attributed to spillover infection of avian H5N1 to harbor seals.

Yesterday, Healthy Wildlife - the blog of the Canadian Wildlife Health Cooperative - reported on an unusual mortality event among seals in the St. Lawrence Estuary, which - by sea - is roughly 1,000 nautical miles from the event in Maine.

First the report from Quebec, then I'll return with a postscript.

Mortalities of harbour seals in the St. Lawrence Estuary in Quebec associated with infections by a highly pathogenic H5N1 avian influenza virus

BY CAROLYN BLUSHKE · 2022-07-12

Over the last few weeks, the Réseau québécois d’urgence pour les mammifères marins has reported an unusually high number of dead or sick harbour seals in the St. Lawrence Estuary. In fact, the number of harbour seals found dead so far this year represents an increase of about 8 times of the annual average of recent years. In order to determine the cause of this exceptional situation, seal carcasses and samples taken in the field were sent for analysis to the Quebec regional centre (CQSAS) for the Canadian Wildlife Health Cooperative.

The results obtained so far indicate that the increase in mortalities observed in these harbour seals are associated with infections by a highly pathogenic Eurasian H5N1 avian influenza virus. In fact, although these results remain to be confirmed by the Canadian Food Inspection Agency, the results obtained by the molecular biology laboratory of the Ministère de l’Agriculture, des Pêcheries et de l’Alimentation du Québec indicate that this virus is present in the majority of seals analyzed. Microscopic lesions characteristic of this viral infection have also been demonstrated in one of the seals autopsied so far. For now, all the positive cases come from the Bas-Saint-Laurent region. These results should be confirmed by Fisheries and Oceans Canada shortly.

The highly pathogenic Eurasian H5N1 avian influenza virus has been circulating in North America since the beginning of the year and has been associated with mortalities in several species of wild birds. It is believed that this virus was transported from Europe by seabirds. In Quebec, this virus has caused the death of several species, including snow geese, Canada geese, common eiders and northern gannets. Several species that feed on dead infected birds, such as turkey vultures, bald eagles, corvids and gulls, have also been affected.

In addition, cases of avian flu have also been diagnosed in North America in mammalian species, including red foxes, striped skunks and raccoons. Cases of harbour seal infections with the H5N1 virus have also recently been reported on the US east coast. It can be hypothesized that seals become infected following contact with infected seabirds, such as common eiders, with which they share the habitat. It is not surprising that harbour seals are susceptible to this virus. Indeed, avian flu epidemics have already been documented in the past in seals on the American east coast as well as in Europe. The impact these mortalities will have on the seal population remains to be determined.

Although the risk of transmission of this influenza virus to humans and domestic animals appears to be low, it is recommended not to approach, and especially not to touch, a sick or dead seal. We should also prevent contact between our domestic animals and dead seals or birds.

Stéphane Lair – RCSF Quebec, Faculté de médecine vétérinaire, Université de Montréal

While the HPAI H5Nx clade 2.3.4.4b virus causing our North American and European avian epizootic remains primarily a threat to birds, over the past couple of years it has increased its ability to infect both terrestrial and marine mammals, raising concerns around the globe (see Nature Why unprecedented bird flu outbreaks sweeping the world are concerning scientists).

At the same time is has increased its ability to spread via some migratory birds (see HPAI Detected In Arctic (Svalbard) For the First Time), while causing high mortality among many other avian species (see DEFRA: The Unprecedented `Order Shift' In Wild Bird H5N1 Positives In Europe & The UK).

HPAI H5 has also developed more persistence, lingering deeper into the summer than in previous years, raising concerns that it could become an enzootic, rather than an epizootic, threat. Human infections remain very rare, and quite mild, but many of spillovers into other mammals have produced severe, often fatal, disease.

Where all of this will lead is unknowable.

We've seemed to be on the precipice with HPAI H5 before - in Southeast Asia, Indonesia, Egypt, and briefly in parts of Europe - and against all expectations the virus sputtered and receded before it could spark a major public health event.

We might get lucky again.

But the HPAI H5 viruses of today are far more diverse, and more widespread (geographically and by species), than they were during the first and second decades of the 21st century.

Which means the usual caveat; that past performance is no guarantee of future results, firmly applies.

For more background on the recent evolution of HPAI H5Nx, you may wish to revisit: