Monthly summary of sampled birds

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The Nextstrain builds are available on the SENTINEL Wild Birds Group - https://nextstrain.org/groups/SentinelWildBirds

September 2025

1. OVERVIEW
SENTINEL Wild Birds aims to enhance the understanding of highly pathogenic avian influenza (HPAI) virus dynamics in wild bird populations by conducting active surveillance at key locations in and near Europe. These locations are divided into the following surveillance nodes: Node 1 Gulf of Finland (Finland, Estonia), Node 2 Southern Baltic Sea (Sweden, Latvia, Lithuania, Poland), Node 4 Eastern Black Sea (Georgia), Node 6 Lake Constance (Germany, Austria, Switzerland), Node 7 Veneto Region (Italy), Node 8 Camargue (France), and Node 9 Gulf of Cadiz (Spain). This monthly summary provides an update on sampled wild birds as part of an early warning system to support wildlife management and disease prevention efforts. The data in this report are based on previously unpublished samples collected from August 2025 to September 2025.

2. RESULT

2.1 DATA COLLECTION
Since the last monthly report (published on 3rd of September 2025; https://doi.org/10.5281/zenodo.17045002), and as of 15th September 2025, test results have been submitted for 454 samples taken from 314 individuals representing 14 taxa from four nodes in Europe (Table 1). Of the 454 collected samples, 225 (50%) were cloacal swabs, 94 (21%) tracheal/oropharyngeal swabs, 57 (13%) combined swabs (choana + cloacal), 46 (10%) choana swabs, and 32 (7%) fecal samples. Of all samples, 13 (<3%) were positive for avian influenza virus, but none were positive for highly pathogenic avian influenza (HPAI) virus (Figure 1; Table 2).

The most sampled species were Mute Swan (94 individuals), Greater Flamingo (92 individuals), and Mallard (67 individuals; Table 1).

TABLE 1 Most recently sampled individuals in the SENTINEL Wild Birds project. Total number of individuals sampled in the wild, as well as number of individuals tested positive for avian influenza virus. The table includes previously unpublished samples from August to September 2025.

FIGURE 1 Sample sites in the SENTINEL Wild Birds project. Sample sites for the 314 individuals sampled in Estonia, Latvia, Lithuania, Austria, Switzerland, and Spain. The figure includes previously unpublished samples from August to September 2025.

TABLE 2 Most recently collected samples in the SENTINEL Wild Birds project. Total number of collected samples as well as number of samples positive for avian influenza virus. The table includes previously unpublished samples from August to September 2025.

A weekly compilation of all 15,167 samples (positive and negative; including previously published), collected at each node from August 2024 to September 2025, can be seen in Figure 2.

FIGURE 2 Weekly summary of collected samples in the SENTINEL Wild Birds project. In total, 15,167 samples (negative samples in blue; avian influenza virus-positive samples in orange) have been collected at seven nodes between August 2024 and September 2025, yielding 1,053 samples positive for avian influenza virus, including 24 samples positive for HPAI virus. The figures also include samples published in previous reports.

2.2 GENOMICS SUMMARY
Since the last report was published on 3rd of September (https://doi.org/10.5281/zenodo.17045002), and as of 15th of September 2025, no new sequences have been generated. The latest and previous Nextstrain builds are available on the SENTINEL Wild Birds Group (https://nextstrain.org/groups/SentinelWildBirds).

3. CONCLUSION
After the summer period with low sampling activity and few detections of avian influenza viruses, sampling has now resumed at several nodes as the autumn migration begins. As expected, both the number of analysed samples and the proportion of positive detections have increased. Waterfowl such as Mute Swans (in Austria and Switzerland) and dabbling ducks, including Mallards and Gadwalls (in Estonia and Latvia), were among the most frequently sampled species. In addition, large numbers of Greater Flamingos were sampled in Spain; however, both the flamingo captures in Spain and the intensive swan trapping around Lake Constance were targeted efforts and will not continue later in the year.

All positive samples were collected in the Baltic countries, most likely from birds at the beginning of their autumn migration. The detected viruses included one H5 and one N8 from Mallards in Estonia, one H12 from a Gadwall in Latvia, and three additional detections from Mallards in Latvia (two N2 and one H4N2). So far, no highly pathogenic avian influenza (HPAI) viruses have been reported, and the overall prevalence remains relatively low.

Nevertheless, the onset of autumn migration marks a critical period when new virus introductions or reassortants can emerge and spread rapidly among staging and wintering waterfowl, especially among juvenile, immuno-naïve individuals. Continued sampling and timely data submission in the coming month will therefore be essential for early detection and risk assessment.

ACKNOWLEDGMENT
This report is based on data collected and analysed by fieldworkers, laboratory personnel, and node coordinators from the following organizations and institutions:

Node 1: LABRIS, Riigi Laboriuuringute ja Riskihindamise Keskus (Estonia); Ruokavirasto, Finnish Food Authority (Finland); University of Turku (Finland)

Node 2: Swedish National Veterinary Institute (SVA) (Sweden); Linnaeus University (Sweden); Institute of Food Safety, Animal Health and Environment “BIOR” (Latvia); National Food and Veterinary Risk Assessment Institute (Lithuania); State Food and Veterinary Service (Lithuania); National Veterinary Research Institute (Poland)

Node 4: Centre of Wildlife Disease Ecology (CWDE), Ilia State University; State Laboratory of Agriculture of Georgia

Node 6: Austrian Agency for Health and Food Safety (AGES) (Austria); Verein für die Betreuung des Naturschutzgebietes Rheindelta (Naturschutzverein Rheindelta) (Austria); Friedrich-Loeffler-Institute (FLI) (Germany); Max-Planck-Institut für Verhaltensbiologie (MPI) (Germany); National Reference Centre for Poultry and Rabbit Diseases (NRGK) (Switzerland); Swiss Institute for Virology and Immunology (IVI) (Switzerland)

Node 7: Istituto Zooprofilattico Sperimentale delle Venezie; Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA)

Node 8: École Nationale Vétérinaire de Toulouse (ENVT); INRAE (Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement); La Tour du Valat; Conservatoire d’Espaces Naturels d’Occitanie (CEN Occitanie); Laboratoire Départemental du Gard; Office Français de la Biodiversité (OFB); Ministère de l’Agriculture et de la Souveraineté Alimentaire; Muséum national d’Histoire naturelle (MNHN); Agence nationale de sécurité sanitaire de l’alimentation, de l’environnement et du travail (ANSES)

Node 9: Martina Ferraguti, Josué Martínez-de la Puente, and Jordi Figuerola at Estación Biológica de Doñana (EBD-CSIC); Ursula Höfle at Grupo de Sanidad y Biotecnología (SaBio), Instituto de Investigación en Recursos Cinegéticos (IREC-CSIC); Elisa Pérez-Ramírez and Jovita Fernández-Pinero at Centro de Investigación en Sanidad Animal (CISA-INIA-CSIC) (Spain)