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

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