Circumpolar spread of avian influenza H5N1 to southern Indian Ocean islands

Since 2020, the outbreak of high pathogenicity avian influenza (HPAI) H5N1 virus clade 2.3.4.4b has turned into the largest documented panzootic <sup>1,3</sup>. Here, we describe its arrival into the Indian Ocean sub-Antarctic archipelagos of Crozet and Kerguelen, where we first detected the virus in October 2024 in dead southern elephant seals. While the panzootic is ongoing, it has already caused unprecedented mortalities of marine mammals and seabirds. We collected brain swabs from seal and seabird carcasses and obtained 25 novel HPAI H5N1 2.3.4.4b sequences. Using phylogeographic analyses, we show that there have been independent introductions of the virus to Crozet and Kerguelen islands, most likely from the distant South Georgia islands in the Southern Atlantic, and not from the more nearby coasts of South Africa. Our results point to a year-long gap in genomic surveillance in the sub-Antarctic region. Locally, our analyses show that the virus is transmitted between different species. Our serological analyses show that some southern elephant seal had mounted an anti-H5 antibody response. Through its circumpolar spread to the Indian Ocean, HPAI H5N1 2.3.4.4b moves closer to Australia, which remains free from infections with this strain, and represents a major threat to the sub-Antarctic wildlife.

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Publication Details

Journal
Nature Communications
Published
2025-09-29
DOI
https://doi.org/10.1038/s41467-025-64297-y
Citations
11
Primary Topic
Influenza Virus Research Studies
Type
article
Field-Weighted Citation Impact
14.90

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article

Circumpolar spread of avian influenza H5N1 to southern Indian Ocean islands

Edouard Hirchaud, Claudia P. Pasquale, Clive R. McMahon, J Tornos et al.
11 citations
Nature Communications
Influenza Virus Research Studies
14.90
article

Circumpolar spread of avian influenza H5N1 to southern Indian Ocean islands

Edouard Hirchaud, Claudia P. Pasquale, Clive R. McMahon, J Tornos, Augustin Clessin, Mathilde Lejeune, Samuel L. Hong, Béatrice Grasland, Thierry Boulinier, François‐Xavier Briand, Florent Souchaud, Guy Baele, Christophe Guinet, Tristan Bralet, R Fischer
article en
11 citations

Abstract

Since 2020, the outbreak of high pathogenicity avian influenza (HPAI) H5N1 virus clade 2.3.4.4b has turned into the largest documented panzootic <sup>1,3</sup>. Here, we describe its arrival into the Indian Ocean sub-Antarctic archipelagos of Crozet and Kerguelen, where we first detected the virus in October 2024 in dead southern elephant seals. While the panzootic is ongoing, it has already caused unprecedented mortalities of marine mammals and seabirds. We collected brain swabs from seal and seabird carcasses and obtained 25 novel HPAI H5N1 2.3.4.4b sequences. Using phylogeographic analyses, we show that there have been independent introductions of the virus to Crozet and Kerguelen islands, most likely from the distant South Georgia islands in the Southern Atlantic, and not from the more nearby coasts of South Africa. Our results point to a year-long gap in genomic surveillance in the sub-Antarctic region. Locally, our analyses show that the virus is transmitted between different species. Our serological analyses show that some southern elephant seal had mounted an anti-H5 antibody response. Through its circumpolar spread to the Indian Ocean, HPAI H5N1 2.3.4.4b moves closer to Australia, which remains free from infections with this strain, and represents a major threat to the sub-Antarctic wildlife.

Nature CommunicationsVol. 16(1)
Centre National de la Recherche Scientifique (FR), École Pratique des Hautes Études (FR), École nationale d'ingénieurs de Brest (FR), Université de Montpellier (FR), Rega Institute for Medical Research (BE), Centre d'Écologie Fonctionnelle et Évolutive (FR), Centre d'Etudes Biologiques de Chizé (FR), Agence Nationale des Fréquences (FR), Sydney Institute of Marine Science (AU), Institut de Recherche pour le Développement (FR), KU Leuven (BE)
Joint Programming Initiative Water challenges for a changing world, Biodiversa+, European Commission, Agence Nationale de la Recherche, Centre National de la Recherche Scientifique, Institut Polaire Français Paul Emile Victor, Vlaamse regering, Office Français de la Biodiversité
Openalex Percentile: Top 1%
Influenza Virus Research Studies
14.90
DOIOpen Access PDFOpenAlex
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