The tragic losses we've seen in South America, with well over 20,000 sea lion deaths, are a grim reminder that avian H5N1 continues to spillover into mammals, and that given enough time, it could learn to better adapt to non-avian hosts.
Once again, severe neurological symptoms were noted, which have been increasingly linked to HPAI H5 infections (see Cell: The Neuropathogenesis of HPAI H5Nx Viruses in Mammalian Species Including Humans).
Due to its length, and technical nature, I've only posted some excerpts. Follow the link to read the report in its entirety.
Influenza A(H5N1) Virus Infections in 2 Free-Ranging Black Bears (Ursus americanus), Quebec, Canada
Benjamin T. Jakobek, Yohannes Berhane, Marie-Soleil Nadeau, Carissa Embury-Hyatt, Oliver Lung, Wanhong Xu, and Stéphane Lair
Wholly Eurasian highly pathogemic avian influenza H5N1 clade 18.104.22.168b virus was isolated from 2 free-ranging black bears with meningoencephalitis in Quebec, Canada. We found that isolates from both animals had the D701N mutation in the polymerase basic 2 gene, previously known to promote adaptation of H5N1 viruses to mammal hosts.
Since its arrival in North America during December 2021, the Eurasian highly pathogenic avian influenza (HPAI) virus subtype H5N1, clade 22.214.171.124b, has been associated with a high mortality rate for wild birds all over the continent (1). Affected bird species include mainly waterfowl and colonial nesting marine birds, as well as scavenger birds, such as gulls, eagles, vultures, and corvids (2,3). As with several other subtypes, HPAI H5N1 can potentially infect persons, although clinical cases in humans have been limited (4). However, this virus has been shown to be pathogenic for different species of wild mammals, including red fox, striped skunk, mink, raccoon, and seals (5–7). Infections with influenza A(H1N1) viruses have been described in captive sloth bears (8). We report and describe infections by HPAI H5N1 virus in 2 black bears (Ursus americanus) found in Quebec, Canada, during the summer of 2022.
Two young-of-the-year black bear cubs (likely born in January‒February) were observed wandering on a road within the Forillon National Park in Gaspé, Quebec, Canada (48°51′39′′N, 64°13′26′′W), on June 14, 2022. The cubs, which were active and quite vocal, were not attended by their dam. Shortly afterward, an adult female bear with unusual behavior was reported ≈200 m from the cubs. This female was wandering between vehicles, fell into a river, and began circling. Upon the arrival of park officials, the animal was in lateral recumbency and convulsing in a ditch.
Because of the severity of the neurologic signs present and concern for public safety, the bear was anesthetized and then euthanized. The 2 cubs, presumed to be orphaned, were also euthanized. The carcasses of the adult female and 1 of the cubs were subsequently frozen. The adult female was thawed a few days later and examined on site. Different organs were sampled, refrozen and shipped, along with the originally frozen cub, to the Canadian Wildlife Health Cooperative Quebec regional center for further macroscopic examination, which was performed on July 7, 2022.
The described black bears were within the Atlantic Americas avian flyway, where Eurasian lineage H5N1 viruses were detected in 2021 (1). The global epizootic of the HPAI H5N1 virus belonging to clade 126.96.36.199b has led to an exceptional number of animal deaths, particularly in domestic poultry and wild birds (12).
As opportunistic omnivores, black bears might be found scavenging on carcasses of dead animals, including birds. Within 5 km and in the 3 weeks preceding the euthanasia of both bears, several dead wild birds tested positive for the Eurasian lineage of HPAI H5N1, including common murre (Uria aalge), American crow (Corvus brachyrhynchos), northern gannet (Morus bassanus), and razorbill (Alca torda) (Canadian Wildlife Health Cooperative internal database, https://www.cwhc-rcsf.caExternal Link).
Suspected deaths of seals caused by HPAI H5N1 had occurred around the same time that the bears were found; however, those seal carcasses were >300 km away, and no suspected or confirmed seal deaths caused by HPAI H5N1 have been reported in seal populations in the Gaspé Peninsula (13). Therefore, it is suspected that the adult female black bear in this study was infected through spillover directly from infected bird carcasses because black bears in the Gaspé Peninsula share habitat with marine birds for which there have been confirmed deaths caused by HPAI H5N1 (13; Canadian Wildlife Health Cooperative internal database) during the same period.
Although H5N1 virus transmission has been documented in mink and ferrets, transmission of the virus between mammals is generally inefficient (14). Therefore, the possibility that the virus that affected these black bears was transmitted from 1 bear to another, or from another mammal species, is much less probable than transmission from birds. Although HPAI virus infections in mammals might occur secondary to other infections, no other infectious agents were identified in either of the black bears.
Dr. Jakobek is a veterinary resident in wildlife health management with the Canadian Wildlife Health Cooperative and the Faculté de Médecine Vétérinaire at the Université de Montréal, Saint-Hyacinthe, Quebec, Canada. His primary research interests are wildlife disease epidemiology and conservation medicine.