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. 2025 May;30(19):2400662.
doi: 10.2807/1560-7917.ES.2025.30.19.2400662.

Human infections with Eurasian avian-like swine influenza virus detected by coincidence via routine respiratory surveillance systems, the Netherlands, 2020 to 2023

Dirk Eggink  1 , Annelies Kroneman  1 , Jozef Dingemans  2 , Gabriel Goderski  1 , Sharon van den Brink  1 , Mariam Bagheri  1 , Pascal Lexmond  3 , Mark Pronk  3 , Erhard van der Vries  4 , Evelien Germeraad  5 , Diederik Brandwagt  1 , Manon Houben  4 , Mariëtte van Hooiveld  6 , Joke van der Giessen  1 , Rianne van Gageldonk-Lafeber  1 , Ron Fouchier  3 , Adam Meijer  1
Affiliations

Human infections with Eurasian avian-like swine influenza virus detected by coincidence via routine respiratory surveillance systems, the Netherlands, 2020 to 2023

Dirk Eggink et al. Euro Surveill. 2025 May.

Abstract

BackgroundZoonotic influenza, including infections with avian and swine influenza A viruses (swIAV), is a notifiable disease in the Netherlands. Human cases infected with swIAV have previously been rarely detected in the Netherlands.AimWe aimed to describe detection and characterisation of Eurasian avian-like swIAV infections in humans in the Netherlands 2020-2023.MethodsThe Dutch National Influenza Center coordinates different activities to monitor respiratory infections and circulating human influenza viruses. This monitoring includes sentinel surveillance in general practitioner practices, community participatory surveillance and characterisation of influenza viruses received from diagnostic laboratories. A subset of the specimens positive for influenza A virus from the monitoring activities are sent for further characterisation. We characterised swIAV from human patients using whole genome sequencing, tested the viruses for antiviral susceptibility and in haemagglutination inhibition assays for antigenic characterisation and compared them with previous detections from humans and pigs.ResultsAvian-like swine influenza virus was detected in three persons presenting with mild respiratory symptoms, and all recovered fully. Only one patient had close contact with pigs shortly before the start of symptoms. Sequence analyses of the viruses showed clustering with swAIV from pigs in a recently initiated surveillance system on pig farms.ConclusionsThese human cases show that swIAV viruses with zoonotic potential are enzootic in the Netherlands. Finding them by coincidence suggests human infections might occur more frequently than noticed.

Keywords: human surveillance; respiratory infections; swine influenza virus; zoonoses.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Subtyped influenza A viruses from humans within surveillance of influenza, the Netherlands, week 40 2019–week 39 2023 (n = 3,931)
Figure 2
Figure 2
Phylogenetic tree of avian-like swine influenza A viruses from human patients (n = 3) and pigs (n = 116), the Netherlands, 2020–2023
Figure 3
Figure 3
Antiviral sensitivity of avian-like swine influenza A viruses isolated from humans and pigs compared to human seasonal influenza viruses, the Netherlands, 2020–2023
See this image and copyright information in PMC

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