Marie-Jeanne Pesant, Université de Montréal

Marie-Jeanne Pesant1, Valérie Grenier Saint-Sauveur2, Shannon Ferrell2,3, Lisa Lee6, Brian Stevens4,5, Stéphane Lair2,3,4, Carl A Gagnon1,2 1. Laboratoire des maladies infectieuses virales vétérinaires, Faculté de médecine vétérinaire, Université de Montréal, Québec, Canada 2. Centre de diagnostic vétérinaire de l'Université de Montréal (CDVUM), Faculté de médecine vétérinaire, Université de Montréal, Québec, Canada 3. Centre québécois sur la santé des animaux sauvages (CQSAS), Faculté de médecine vétérinaire, Université de Montréal, Québec, Canada 4. Canadian Wildlife Health Cooperative – Réseau canadien pour la santé de la faune (CWHS-RCSF), Canada 5. Department of Pathobiology, Ontario Veterinary College, University of Guelph, Ontario, Canada 6. Animal Health Center, Ministry of Agriculture and Food, British-Columbia, Canada

Discovering & Evolving

The American crow (Corvus brachyrynchos) is an important bioindicator species for West Nile virus and many Canadian disease monitoring programs call out to the general population to signal deceased animals. Many xases of orthoreovirus infection in crows have been reported in North-America. Between 2022 and 2025, 23 sick or deceased birds across Canada (on-site mortalities ranging from an individual to groups of 60) were reported by civilians and rapidly retrieved by respective wildlife health surveillance activities. 43,5% of the infected birds were found dead between January and April which fits the event referred as epizootic "winter mortalities of crows". The birds were necropsied at different wildlife disease Centers and those showing signs of orthoreovirus infection (necro-hemorrhagic enteritis, splenomegaly and fibrinecrotic splenitis) had intestine or spleen submitted to the CDVUM for molecular testing (inhouse corvid orthoreovirus-specific RT-qPCR). In most cases, intestine samples had higher viral loads than spleen samples. Of the 17 RT-qPCR positive cases (Ct <35), 15 (Ct <32) had their partial sigmaC (protein of the S1 segment) successfully sequenced (989 nt long). Fifteen new sequences were hence obtained from Quebec (n=7), Ontario (n=3) and British-Columbia (n=5). Phylogenetic analysis revealed high homology with older cases of orthoreovirus from American crows (United-States), from a Carrion crow (Japan) and from a Hooded crow (Finland). Interestingly, our Canadian cases clustered within regional locations even though these had > 89% nucleotide identity. These first Canadian Corvus brachyrynchos reovirus sequences strengthen the 2019 new Orthoreovirus neoavis species and even push towards a corvid-specific species demarcation.