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. 2022 Aug 30;13(4):e0060922.
doi: 10.1128/mbio.00609-22. Epub 2022 Jun 21.

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

Anne Pohlmann #  1 , Jacqueline King #  1 , Alice Fusaro  2 , Bianca Zecchin  2 , Ashley C Banyard  3   4 , Ian H Brown  3   4 , Alexander M P Byrne  3 , Nancy Beerens  5 , Yuan Liang  6 , Rene Heutink  5 , Frank Harders  5 , Joe James  3   4 , Scott M Reid  3 , Rowena D E Hansen  3 , Nicola S Lewis  7 , Charlotte Hjulsager  8 , Lars E Larsen  6 , Siamak Zohari  9 , Kristofer Anderson  9 , Caroline Bröjer  10 , Alexander Nagy  11 , Vladimir Savič  12 , Steven van Borm  13 , Mieke Steensels  13 , Francois-Xavier Briand  14 , Edyta Swieton  15 , Krzysztof Smietanka  15 , Christian Grund  1 , Martin Beer  1 , Timm Harder  1
Affiliations

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

Anne Pohlmann et al. mBio. .

Abstract

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.

Keywords: Europe; enzootic; enzootic evolution; evolution; high-pathogenicity avian influenza; migratory birds; poultry.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

FIG 1
FIG 1
Time-scaled maximum clade credibility (MCC) phylogeny of hemagglutinin (HA) sequences of HPAIV collected between August 2020 and November 2021 (scale at the bottom) in wild birds (colored round tips), poultry (black square tips), and mammals (red triangle tips) of European countries. Country colors are ordered from northeast to southwest. Two distinct branches, B1 and B2, as well as the times and subtypes of different sublineages are depicted. The two arrows indicate a time gap during the summer period in branches B1 and B2.
FIG 2
FIG 2
Genotype-based panoramic scope of reassortant HPAIV H5N1 detected in Europe in 2021. Maximum likelihood (ML) trees of concatenated coding sequences of full genomes were generated with RAxML. A polar tree layout with proportional transformed branches was used for visualization. The genome composition is sketched with appropriately colored segments for each genotype; major genotypes are also shown as schematic virions.
See this image and copyright information in PMC

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