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

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By G.M.

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 Ekkerøy 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 Ekkerøy 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 α2,3-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.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.05.23.655725v1

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