Highly Pathogenic Avian Influenza A(H5N1) Caused Mass Death among Black-legged Kittiwakes (Rissa tridactyla) in Norway, 2023

Romo, G.; Piercey Akesson, C.; Reiertsen, T. K.; Fosse, J. H.; Arnason Boe, C.; Austbo, L.; Akerstedt, J.; Saghafian, M.; Helberg, M.; Hungnes, O.; Gjerset, B.; Granstad, S.; Hogseth, G.; Lotvedt, S.; Dosen, A.; Tonnessen, R.

doi:10.1101/2025.05.23.655725

bioRxiv · 10.1101/2025.05.23.655725

Highly Pathogenic Avian Influenza A(H5N1) Caused Mass Death among Black-legged Kittiwakes (Rissa tridactyla) in Norway, 2023

Romo, G.·Piercey Akesson, C.·Reiertsen, T. K.·Fosse, J. H.·Arnason Boe, C.·Austbo, L.·Akerstedt, J.·Saghafian, M.·Helberg, M.·Hungnes, O.·Gjerset, B.·Granstad, S.·Hogseth, G.·Lotvedt, S.·Dosen, A.·Tonnessen, R.

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Abstract

In 2023, highly pathogenic avian influenza (HPAI) heavily affected gulls in Europe. In July, a mass mortality event was reported in the Black-legged Kittiwake (Rissa tridactyla) breeding colony at Ekkeroy in Northern Norway. The cause was confirmed to be infection with the HPAI H5N1 clade 2.3.4.4b virus, genotype EA-2022-BB. We describe the outbreak in Kittiwakes, including pathological and virological investigations, and discuss the management and zoonotic potential. With more than 15,000 dead birds reported, we estimate that the outbreak caused a reduction in the Kittiwake population at Ekkeroy of at least 50%. Diseased birds exhibited neurological signs. Necropsy of ten birds revealed a peracute fatal systemic disease, with severe lesions in the brain and pancreas co-localizing with the presence of viral RNA and antigen. Vascular expression of 2,3-linked sialic acids and viral RNA/antigen may reflect hematogenous virus spread. Further studies should investigate the long-term impact of HPAI on Kittiwake populations.

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Romo, G., Piercey Akesson, C., Reiertsen, T. K., Fosse, J. H., Arnason Boe, C., Austbo, L., Akerstedt, J., Saghafian, M., Helberg, M., Hungnes, O., Gjerset, B., Granstad, S., Hogseth, G., Lotvedt, S., Dosen, A., Tonnessen, R.. 2025-05-23. Highly Pathogenic Avian Influenza A(H5N1) Caused Mass Death among Black-legged Kittiwakes (Rissa tridactyla) in Norway, 2023. https://doi.org/10.1101/2025.05.23.655725

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