Annual report on surveillance for avian influenza in poultry and wild birds in Member States of the European Union in 2021

Transmission dynamics of highly pathogenic avian influenza among multiple waterfowl species and backyard poultry: the impact of the stopover period

Spillover of Highly Pathogenic Avian Influenza (HPAI) to backyard poultry via migratory birds threatens the poultry industry and public health. To improve the understanding of spillover events, we developed a stochastic compartmental mathematical model of HPAI transmission dynamics at the waterfowl-backyard poultry interface in a high-risk area for HPAI introduction into poultry. The model described the infection spread among resident and migratory waterfowl and backyard poultry farms and was validated with historical outbreak data in backyard poultry farms and swan mortalities. We used the model to assess the impact of the timing and duration of migratory birds' stopover period on the probability of HPAI infection in backyard poultry farms. Additionally, we predicted mortality in a sentinel bird species and assessed the impact of HPAI virulence and immunity in a resident reservoir species on the HPAI transmission dynamics. The stopover duration of the reservoir species predicts the HPAI infection probability in backyard poultry farms from waterfowl communities, but the stopover timing has no effect. HPAI virus virulence and immunity against the virus impact the transmission risk to backyard poultry. Understanding factors influencing reservoir species' migration stopover duration in a location will aid HPAI outbreak forecasting and control in backyard poultry farms.

European Food Safety Authority (EFSA), Abrahantes JC, Aznar I, Catalin I, Kohnle L, Mulligan KF, Mur L, Stoicescu A, van Houtum A, Zancanaro G. Avian influenza annual report 2023

All European Union (EU) Member States (MSs), along with Iceland, Norway, Switzerland and the United Kingdom (Northern Ireland), conduct surveillance for avian influenza (AI) in poultry and wild birds. EFSA, upon mandate of the European Commission, compiles and analyses this data in an annual report. This summary highlights findings from the 2023 surveillance activities. In 2023, 31 reporting countries (RCs) visited 21,183 poultry establishments (PEs). Of these, 18,557 underwent serological investigations, 2460 underwent virological investigations and 166 underwent both. Among the 18,723 PEs sampled for serological testing, 29 PEs (0.15%) were seropositive for influenza A(H5/H7) viruses, more in detail: 27 PEs tested positive for A(H5), 1 tested positive for A(H7) and 1 tested positive for both strains. These were found in eight RCs (Bulgaria, Poland, Germany, Spain, Sweden, Norway, Iceland and Finland). Of the 2626 PEs sampled for virological testing, 180 PEs (6.85%) were positive for influenza A(H5/H7) viruses. More precisely, 178 tested positive for A(H5), of which 161 positive for HPAI (H5N1) and 2 tested positive for A(H7). Positive PEs were reported by 12 RCs covering 14 different poultry categories. A total of 51,411 wild birds were sampled, with 6717 (13.07%) testing positive for HPAIVs by PCR from 25 RCs. Subtype A(H5N1) was the main influenza A virus identified (6531; 97%), similar to 2022. Twenty RCs reported 1940 wild birds testing positive for LPAI or AIV of unknown pathogenicity. For these, 1372 (67.5%) were nor A(H5) or A(H7), while 568 (29.3%) tested positive for A(H5). These findings reflect the ongoing efforts in early detection and monitoring of avian influenza to mitigate the risk of outbreaks in poultry populations throughout Europe.

Emergence of highly pathogenic avian influenza viruses H5N1 and H5N5 in white-tailed eagles, 2021-2023

Highly pathogenic avian influenza (HPAI) poses a substantial threat to several raptors. Between 2021 and 2023, HPAI viruses (HPAIVs) of the Goose/Guangdong lineage H5 clade 2.3.4.4b became widespread in wild birds in Norway, and H5N1 and H5N5 viruses were detected in 31 white-tailed eagles (Haliaeetus albicilla, WTEs). Post-mortem examinations of four WTEs revealed no macroscopic pathological findings. Microscopic examinations showed the presence of myocardial and splenic necroses and a few lesions in the brain. In situ hybridization revealed the presence of the virus in several organs, suggesting a multisystemic infection. The detection of HPAIV H5N5 in a WTE in February 2022 marked the first recorded occurrence of this subtype in Norway. Since then, the virus has persisted, sporadically being detected in WTEs and other wild bird species. Phylogenetic analyses reveal that at least two distinct incursions of HPAIV H5N1 Eurasian (EA) genotype C affected WTEs, likely introduced by migratory birds from Eurasia and seabirds entering from Western and Central Europe. Some WTE isolates from 2021 to 2022 clustered with those from Canada and Ireland, aligning with the transatlantic spread of H5N1. Others were related to the 2021 mass mortality of great skuas in the UK or outbreaks in seabird populations, including gannets, gulls and terns, during 2022 in the North Sea region. This suggests that the WTEs were likely preying on the affected birds. Our study highlights that WTEs can act as sentinels for some HPAIV strains, but the absence of several known circulating genotypes in WTEs suggests varying pathogenic effects on this species.

Highly Pathogenic Avian Influenza (HPAI) H5 Clade 2.3.4.4b Virus Infection in Birds and Mammals

Avian influenza viruses (AIVs) are highly contagious respiratory viruses of birds, leading to significant morbidity and mortality globally and causing substantial economic losses to the poultry industry and agriculture. Since their first isolation in 2013-2014, the Asian-origin H5 highly pathogenic avian influenza viruses (HPAI) of clade 2.3.4.4b have undergone unprecedented evolution and reassortment of internal gene segments. In just a few years, it supplanted other AIV clades, and now it is widespread in the wild migratory waterfowl, spreading to Asia, Europe, Africa, and the Americas. Wild waterfowl, the natural reservoir of LPAIVs and generally more resistant to the disease, also manifested high morbidity and mortality with HPAIV clade 2.3.4.4b. This clade also caused overt clinical signs and mass mortality in a variety of avian and mammalian species never reported before, such as raptors, seabirds, sealions, foxes, and others. Most notably, the recent outbreaks in dairy cattle were associated with the emergence of a few critical mutations related to mammalian adaptation, raising concerns about the possibility of jumping species and acquisition of sustained human-to-human transmission. The main clinical signs and anatomopathological findings associated with clade 2.3.4.4b virus infection in birds and non-human mammals are hereby summarized.

Genetic Diversity of Avian Influenza Viruses Detected in Waterbirds in Northeast Italy Using Two Different Sampling Strategies

Avian influenza viruses (AIVs), which circulate endemically in wild aquatic birds, pose a significant threat to poultry and raise concerns for their zoonotic potential. From August 2021 to April 2022, a multi-site cross-sectional study involving active AIV epidemiological monitoring was conducted in wetlands of the Emilia-Romagna region, northern Italy, adjacent to densely populated poultry areas. A total of 129 cloacal swab samples (CSs) and 407 avian faecal droppings samples (FDs) were collected, with 7 CSs (5.4%) and 4 FDs (1%) testing positive for the AIV matrix gene through rRT-PCR. A COI-barcoding protocol was applied to recognize the species of origin of AIV-positive FDs. Multiple low-pathogenic AIV subtypes were identified, and five of these were isolated, including an H5N3, an H1N1, and three H9N2 in wild ducks. Following whole-genome sequencing, phylogenetic analyses of the hereby obtained strains showed close genetic relationships with AIVs detected in countries along the Black Sea/Mediterranean migratory flyway. Notably, none of the analyzed gene segments were genetically related to HPAI H5N1 viruses of clade 2.3.4.4b isolated from Italian poultry during the concurrent 2021-2022 epidemic. Overall, the detected AIV genetic diversity emphasizes the necessity for ongoing monitoring in wild hosts using diverse sampling strategies and whole-genome sequencing.

European Food Safety Authority (EFSA), Aznar I, Kohnle L, Stoicescu A, van Houtum A, Zancanaro G. Annual report on surveillance for avian influenza in poultry and wild birds in Member States of the European Union in 2022

All European Union (EU) Member States (MSs) are required to implement surveillance for avian influenza (AI) in poultry and wild birds and (i) to notify the outbreaks, when relevant and (ii) to report the results to the responsible authority. In addition, Iceland, Norway, Switzerland and the United Kingdom (Northern Ireland) also implement ongoing surveillance programmes to monitor occurrences of avian influenza viruses (AIVs) in poultry and wild birds. EFSA received a mandate from the European Commission to collate, validate, analyse and summarise the data resulting from these AI surveillance programmes in an annual report. The present report summarises the results of the surveillance activities carried out in MSs, Iceland, Norway, Switzerland and the United Kingdom (Northern Ireland) in 2022. Overall, the 31 reporting countries (RCs) sampled 22,171 poultry establishments (PEs) during the 2022 surveillance activity: 18,490 PEs were sampled for serological testing and 3775 were sampled for virological testing. Some PEs were therefore sampled for both type of analytical methods. Out of the 18,490 PEs sampled for serological testing, 15 (0.08%) were seropositive for influenza A(H5) viruses. Out of the 3775 PEs sampled for virological testing, 74 PEs (1.96%) were positive to the virological assay for influenza A(H5) viruses. Seropositive PEs were found in four RCs (Belgium, Poland, Spain and Sweden) and as in previous years, the highest percentages of seropositive PEs were found in PEs raising breeding geese and waterfowl game birds. Out of these 15 seropositive PEs, 3 also tested positive by polymerase chain reaction (PCR) for influenza A (H5) viruses - 2 for highly pathogenic avian influenza virus (HPAIV) and 1 low pathogenic avian influenza (LPAI) (H5N3). In relation to the virological surveys, 10 RCs (32%) out of the 31 reported the detection of A (H5) viruses in 74 PEs, covering 12 different poultry categories. More specifically, 54 reported HPAIV A(H5N1), 17 HPAIV (H5N8), 2 AIV (H5N1) with unknown virus pathogenicity and 1 low pathogenic avian influenza (LPAI) (H5N3). Additionally, six PEs tested positive for undefined AIVs in three RCs. A total of 32,143 wild birds were sampled, with 4163 (12.95%) wild birds testing positive for HPAIVs by PCR, from 25 RCs. In contrast to previous years, out of the 4163 wild birds testing positive for HPAIv, subtype A(H5N1) virus was the main influenza A virus subtype identified among the wild bird testing positive for HPAIVs (3942; 95%). In addition, RCs also reported 984 wild birds testing positive for low pathogenic avian influenza (LPAI). Out of those, for 660 (67%) it was ascertained that the subtype was non-A(H5/H7); 260 (26%) wild birds tested positive for LPAIv of A(H5 or H7) subtypes and the remaining 64 (7%) LPAI viruses were belonging to other H-subtypes.

Can Citizen Science Contribute to Avian Influenza Surveillance?

Global change is an important driver of the increase in emerging infectious diseases in recent decades. In parallel, interest in nature has increased, and different citizen science platforms have been developed to record wildlife observations from the general public. Some of these platforms also allow registering the observations of dead or sick birds. Here, we test the utility of live, sick and dead observations of birds recorded on the platform Observation.org for the early detection of highly pathogenic avian influenza virus (HPAIV) outbreaks in the wild in Belgium and The Netherlands. There were no significant differences in the morbidity/mortality rate through Observation.org one to four weeks in advance. However, the results show that the HPAIV outbreaks officially reported by the World Organisation for Animal Health (WOAH) overlapped in time with sudden increases in the records of sick and dead birds in the wild. In addition, in two of the five main HPAIV outbreaks recorded between 2016 and 2021, wild Anseriformes mortality increased one to two months before outbreak declaration. Although we cannot exclude that this increase was related to other causes such as other infectious diseases, we propose that Observation.org is a useful nature platform to complement animal health surveillance in wild birds. We propose possible approaches to improve the utility of the platform for pathogen surveillance in wildlife and discuss the potential for HPAIV outbreak detection systems based on citizen science to complement current surveillance programs of health authorities.