Has Epizootic Become Enzootic? Evidence for a Fundamental Change in the Infection Dynamics of Highly Pathogenic Avian Influenza in Europe, 2021

• Published in: mBio Vol. 13; no. 4; p. e0060922
• Main Authors: Pohlmann, Anne, King, Jacqueline, Fusaro, Alice, Zecchin, Bianca, Banyard, Ashley C., Brown, Ian H., Byrne, Alexander M. P., Beerens, Nancy, Liang, Yuan, Heutink, Rene, Harders, Frank, James, Joe, Reid, Scott M., Hansen, Rowena D. E., Lewis, Nicola S., Hjulsager, Charlotte, Larsen, Lars E., Zohari, Siamak, Anderson, Kristofer, Bröjer, Caroline, Nagy, Alexander, Savič, Vladimir, van Borm, Steven, Steensels, Mieke, Briand, Francois-Xavier, Swieton, Edyta, Smietanka, Krzysztof, Grund, Christian, Beer, Martin, Harder, Timm
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 30.08.2022
• Subjects: Animals; Animals Animals, Wild Birds Europe / epidemiology Influenza A Virus, H5N1 Subtype / genetics Influenza A virus / genetics Influenza in Birds / epidemiology Phylogeny Poultry; Animals, Wild; Birds; enzootic; Europe; Europe - epidemiology; evolution; high-pathogenicity avian influenza; Influenza A virus - genetics; Influenza A Virus, H5N1 Subtype - genetics; Influenza in Birds - epidemiology; Life Sciences; migratory birds; Opinion/Hypothesis; Phylogeny; Poultry; Virology; Europe; enzootic evolution; poultry; high-pathogenicity avian influenza; Europe; evolution; migratory birds; enzootic
• ISSN: 2150-7511; 2161-2129; 2150-7511
• DOI: 10.1128/mbio.00609-22

Phylogenetic evidence from the recent resurgence of high-pathogenicity avian influenza (HPAI) virus subtype H5N1, clade 2.3.4.4b, observed in European wild birds and poultry since October 2021, suggests at least two different and distinct reservoirs. We propose contrasting hypotheses for this emergence: (i) resident viruses have been maintained, presumably in wild birds, in northern Europe throughout the summer of 2021 to cause some of the outbreaks that are part of the most recent autumn/winter 2021 epizootic, or (ii) further virus variants were reintroduced by migratory birds, and these two sources of reintroduction have driven the HPAI resurgence. Phylogenetic evidence from the recent resurgence of high-pathogenicity avian influenza (HPAI) virus subtype H5N1, clade 2.3.4.4b, observed in European wild birds and poultry since October 2021, suggests at least two different and distinct reservoirs. We propose contrasting hypotheses for this emergence: (i) resident viruses have been maintained, presumably in wild birds, in northern Europe throughout the summer of 2021 to cause some of the outbreaks that are part of the most recent autumn/winter 2021 epizootic, or (ii) further virus variants were reintroduced by migratory birds, and these two sources of reintroduction have driven the HPAI resurgence. Viruses from these two principal sources can be distinguished by their hemagglutinin genes, which segregate into two distinct sublineages (termed B1 and B2) within clade 2.3.4.4b, as well as their different internal gene compositions. The evidence of enzootic HPAI virus circulation during the summer of 2021 indicates a possible paradigm shift in the epidemiology of HPAI in Europe.