tetano
Editor, Senior Moderator
Emerg Microbes Infect
. 2026 Dec;15(1):2686474.
doi: 10.1080/22221751.2026.2686474. Epub 2026 Jul 8.
Characterization of oseltamivir-resistant A(H5N1) clade 2.3.4.4b, genotype D1.1 variants identified in poultry farms of British Columbia, Canada
Maxime Cochin[SUP] 1 2 [/SUP], Yacine Abed[SUP] 2 [/SUP], Robert Vendramelli[SUP] 3 [/SUP], Katrina Dionne[SUP] 4 5 [/SUP], Catherine Bourassa[SUP] 5 [/SUP], Geneviève Laroche[SUP] 6 [/SUP], Rose Chan[SUP] 3 [/SUP], Thang Truong[SUP] 3 [/SUP], Anthony Signore[SUP] 7 [/SUP], Yohannes Berhane[SUP] 7 8 9 10 [/SUP], Marceline Côté[SUP] 6 [/SUP], Andres Finzi[SUP] 4 5 [/SUP], Darwyn Kobasa[SUP] 3 11 [/SUP], Guy Boivin[SUP] 1 2 [/SUP]
Affiliations
Highly pathogenic avian influenza A(H5N1) viruses of clade 2.3.4.4b, genotype D1.1, are responsible for widespread outbreaks in poultry and continue to cause sporadic, sometimes severe, human infections. Herein, we characterized a wild-type (WT) influenza A(H5N1) D1.1 isolate (BC-H5N1-WT) and its H275Y neuraminidase (NA) variant (BC-H5N1-H275Y), both of which emerged on farms in British Columbia, Canada, during the fall 2024 outbreak. In vitro analysis assessed replication kinetics in MDCK cells, with supernatants collected at different days post-infection (p.i.) and titrated by TCID[SUB]50[/SUB] and qRT-PCR. Neuraminidase inhibitor (NAI) susceptibility was determined by NA inhibition assays, whereas susceptibility to baloxavir acid (BXA) was evaluated by plaque reduction assay. In vivo virulence was evaluated in BALB/c mice infected with serial 10-fold dilutions of each virus to monitor weight loss and mortality. Viral titers in lungs, brain, nose, kidney, spleen, and heart were quantified at day 4 p.i. The BC-H5N1-WT virus was susceptible to the four antivirals tested, whereas BC-H5N1-H275Y displayed resistance to oseltamivir and peramivir but remained susceptible to zanamivir and BXA. The BC-H5N1-WT exhibited significantly higher viral replication titers than BC-H5N1-H275Y at all tested time points and showed larger plaque sizes. In mice, BC-H5N1-WT was more virulent with LD[SUB]50[/SUB] values of 1.78 × 10[SUP]3[/SUP] PFUs compared to 8.71 × 10[SUP]4[/SUP] PFUs for BC-H5N1-H275Y, and produced higher viral titers in lungs and other organs. Despite the reduced fitness of the resistant H5N1 D1.1 variant, its emergence in the absence of viral selection pressure underscores the need for continued surveillance.
Keywords: A(H5N1); Avian Influenza; H5 clade 2.3.4.4b; NA H275Y; oseltamivir resistance.
. 2026 Dec;15(1):2686474.
doi: 10.1080/22221751.2026.2686474. Epub 2026 Jul 8.
Characterization of oseltamivir-resistant A(H5N1) clade 2.3.4.4b, genotype D1.1 variants identified in poultry farms of British Columbia, Canada
Maxime Cochin[SUP] 1 2 [/SUP], Yacine Abed[SUP] 2 [/SUP], Robert Vendramelli[SUP] 3 [/SUP], Katrina Dionne[SUP] 4 5 [/SUP], Catherine Bourassa[SUP] 5 [/SUP], Geneviève Laroche[SUP] 6 [/SUP], Rose Chan[SUP] 3 [/SUP], Thang Truong[SUP] 3 [/SUP], Anthony Signore[SUP] 7 [/SUP], Yohannes Berhane[SUP] 7 8 9 10 [/SUP], Marceline Côté[SUP] 6 [/SUP], Andres Finzi[SUP] 4 5 [/SUP], Darwyn Kobasa[SUP] 3 11 [/SUP], Guy Boivin[SUP] 1 2 [/SUP]
Affiliations
- PMID: 42419257
- DOI: 10.1080/22221751.2026.2686474
Highly pathogenic avian influenza A(H5N1) viruses of clade 2.3.4.4b, genotype D1.1, are responsible for widespread outbreaks in poultry and continue to cause sporadic, sometimes severe, human infections. Herein, we characterized a wild-type (WT) influenza A(H5N1) D1.1 isolate (BC-H5N1-WT) and its H275Y neuraminidase (NA) variant (BC-H5N1-H275Y), both of which emerged on farms in British Columbia, Canada, during the fall 2024 outbreak. In vitro analysis assessed replication kinetics in MDCK cells, with supernatants collected at different days post-infection (p.i.) and titrated by TCID[SUB]50[/SUB] and qRT-PCR. Neuraminidase inhibitor (NAI) susceptibility was determined by NA inhibition assays, whereas susceptibility to baloxavir acid (BXA) was evaluated by plaque reduction assay. In vivo virulence was evaluated in BALB/c mice infected with serial 10-fold dilutions of each virus to monitor weight loss and mortality. Viral titers in lungs, brain, nose, kidney, spleen, and heart were quantified at day 4 p.i. The BC-H5N1-WT virus was susceptible to the four antivirals tested, whereas BC-H5N1-H275Y displayed resistance to oseltamivir and peramivir but remained susceptible to zanamivir and BXA. The BC-H5N1-WT exhibited significantly higher viral replication titers than BC-H5N1-H275Y at all tested time points and showed larger plaque sizes. In mice, BC-H5N1-WT was more virulent with LD[SUB]50[/SUB] values of 1.78 × 10[SUP]3[/SUP] PFUs compared to 8.71 × 10[SUP]4[/SUP] PFUs for BC-H5N1-H275Y, and produced higher viral titers in lungs and other organs. Despite the reduced fitness of the resistant H5N1 D1.1 variant, its emergence in the absence of viral selection pressure underscores the need for continued surveillance.
Keywords: A(H5N1); Avian Influenza; H5 clade 2.3.4.4b; NA H275Y; oseltamivir resistance.