First case of highly pathogenic H5N1 avian influenza virus infection in a black bear

An adult female black bear exhibiting unusual behaviour was reported by visitors in June at Forillon National Park in the Gaspésie region, Quebec. This bear was exhibiting strange behaviour early in the day on June 14.  It wandered between vehicles, went down to the water in a fishing harbour, began to swim around in circles, came out and hit a wall. Later that day, Parks Canada staff found the animal lying on its side in a ditch breathing shallowly and unresponsive to sound stimuli. Convulsions and spasms were also observed. Due to its condition, the animal was anesthetized by Parks Canada employees and then euthanized for humanitarian reasons. Various organs sampled by park employees were sent to the RCSF-Quebec for analysis.

Microscopic examination of the tissues revealed the presence of inflammatory lesions in the animal’s brain (meningoencephalitis). These lesions were characterized by a significant perivascular accumulation of lymphoplasmacytic cells. This same type of cell also infiltrated the meninges. Neuronal necrosis was also present. Molecular analyzes carried out by the MAPAQ laboratory revealed the presence of a highly pathogenic H5N1 avian influenza virus (H5N1 AIV) in the brain. This result was confirmed by the CFIA laboratory. The results of these examinations therefore indicate that the neurological signs observed in this bear were due to inflammation of the brain caused by an infection with the H5N1 AIV virus. This virus, which appeared in North America last winter, has so far been associated with significant mortalities in several species of wild birds. Three groups of birds have been particularly affected by this virus so far: waterfowl (geese and ducks), scavenger birds (gulls, vultures, corvids and bald eagles) and colonial seabirds (common eiders and gannets). Although much less common than infections in birds, fatal infections have also been reported in a few species of mammals, including red foxes, raccoons, striped skunks and harbour seals. The case described here is, to our knowledge, the first case of fatal infection by an H5N1 AIV in a bear. We can hypothesize that this animal became infected by consuming the carcasses of seabirds on the shores of the park. In fact, H5N1 AIV infections have been documented during the months of May and June in the region in several seabirds, including northern gannet, razorbill, surf scoter and common guillemot. This mode of infection (by ingestion) is the proposed mode of contamination for all mammalian species except seals.

The documentation of these cases of infection in mammalian species can help us better understand which genetic modifications can potentially promote infections in mammals, including humans.

Although the risk of transmission of this avian influenza virus to humans and domestic animals seems low, it is recommended not to approach, and especially not to touch a sick or dead animal. We will also prevent contact between our pets and dead wild birds or mammals. Additionally, although the risks are low, it is recommended that meat from game birds or mammalian species, which can potentially consume infected birds, be thoroughly cooked. Recommendations related to hunting and avian flu can be consulted on the following web page: https://www.canada.ca/en/public-health/services/flu-influenza/fact-sheet-guidance-on-precautions-handling-wild-birds.html

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