Since 2020, a significant increase in the severity of H5Nx highly pathogenic avian influenza (HPAI) epidemics in poultry and wild birds has been observed in Poland. To further investigate the genetic diversity of HPAI H5Nx viruses of clade 2.3.4.4b, HPAIV‐positive samples collected from dead wild birds in 2020–2022 were phylogenetically characterized. In addition, zoonotic potential and possible reassortment between HPAIVs and LPAIVs circulating in the wild avifauna in Poland have been examined. The genome‐wide phylogenetic analysis revealed the presence of three different avian influenza virus (AIV) subtypes (H5N8, H5N5, and H5N1) during the HPAI 2020/2021 season, while in the next HPAI 2021/2022 epidemic only one H5N1 subtype encompassing seven various genotypes (G1–G7) was confirmed. No reassortment events between LPAIVs (detected in the framework of active surveillance) and HPAIVs circulating in Poland have been captured, but instead, epidemiological links between wild birds and poultry due to bidirectional, i.e., wild bird‐to‐poultry and poultry‐to‐wild bird HPAIV transmission were evident. Furthermore, at least five independent H5N8 HPAIV introductions into the Baltic Sea region related to unprecedented mass mortality among swans in February–March 2021 in Poland, as well as a general tendency of current H5Nx viruses to accumulate specific mutations associated with the ability to break the interspecies barrier were identified. These results highlight the importance of continuous active and passive surveillance for AI to allow a rapid response to emerging viruses.

Bornaviruses are a diverse family of viruses infecting various hosts, including birds. Aquatic bird bornavirus 1 (ABBV-1) and aquatic bird bornavirus 2 (ABBV-2) have been found in wild waterfowl but data on their prevalence are scarce. To gain knowledge on the occurrence of ABBVs in Poland, samples originating from dead birds of the Anseriformes order collected in 2016–2021 were tested with a real time RT-PCR method targeting the ABBVs genome. A total of 514 birds were examined, including 401 swans, 96 ducks and 17 geese. The presence of ABBV-1 RNA was detected in 52 swans (10.1% of all tested birds) from 40 different locations. No positive results were obtained for ducks and geese. Sequences of about 2300 bases were generated for 18 viruses and phylogenetic analysis was performed. A relatively low genetic diversity of the examined ABBV-1 strains was observed as all were gathered in a single cluster in the phylogenetic tree and the minimum nucleotide identity was 99.14%. The Polish strains were closely related to ABBV-1 identified previously in Denmark and Germany, but a limited number of sequences from Europe hinders the drawing of conclusions about interconnections between Polish and other European ABBVs. The results of the present study provide new insights into the distribution and genetic characteristics of ABBVs in wild birds in Europe.

The growing importance of the Usutu virus (USUV) as an emerging zoonotic viral pathogen motivated Poland to investigate the epidemiological status of USUV infections among native bird species. Consequently, out of the 357 birds tested, 34 avian individuals from different geographical areas of the country were confirmed to be USUVpositive by RT‒PCR between July and November 2023. The phylogenetic analysis revealed the first recorded occurrence of the USUV Africa 2 and Africa 3 genetic lineages in Poland.

Infectious bronchitis virus (IBV) of the GI-23 lineage, which first emerged in the Middle East in the late 1990s, has since spread worldwide. The factors driving its expansion, whether human involvement, wild bird migration, or the virus’s biological traits, are still unclear. This study aimed to trace the genome evolution of GI-23 IBV in chickens and its adaptability to quails, which are susceptible to both gamma- and deltacoronaviruses. Thirty specific-pathogen-free (SPF) birds, aged between two and three weeks, were used. Initially, three birds were inoculated with the G052/2016 IBV via the oculo-nasal route. On the third day post-infection (dpi), oropharyngeal swabs were collected from the whole group, pooled, and subsequently used to infect three next birds. This process was repeated nine more times during consecutive IBV passages (P-I–P-X), and eventually, virus sequencing was performed using Next-Generation Sequencing (NGS). The obtained results showed that quails were not susceptible to the IBV GI-23 lineage, as the virus RNA was detected in low amounts only during the first passage (QP-I) with no further detections in later rounds of IBV passaging. In chickens, only mild diarrhea symptoms appeared in a few individuals. The NGS analysis identified sixty-two single nucleotide variants (SNVs), thirty of which caused amino acid changes, twenty-eight were synonymous, and one SNV introduced a stop codon. Three SNVs were found in untranslated regions. However, none of these SNVs lasted beyond seven passages, with forty-four being unique SNVs. The Shannon entropy values measured during passages varied for pol1a, pol1b, S, 5a, 5b, and N genes, with overall genome complexity peaking at CP-VI and CP-X. The highest complexity was observed in the pol1a (CP-X) and S genes (CP-IV, CP-VI, CP-VIII, and CP-X). Along with the S gene that was under positive selection, eight codons in pol1a were also positively selected. These findings suggest that even in an adapted host, IBV variability does not stabilize without immune pressure, indicating continuous molecular changes within its genome.

The growing importance of the Usutu virus (USUV) as an emerging zoonotic viral pathogen prompted Poland to investigate the epidemiological status of USUV infections among native bird species. Consequently, thirty-four avian individuals (n = 34) from different geographical parts of the country were confirmed to be USUV-positive in the RT-PCR between July and November 2023. The phylogenetic analysis indicates the first-ever recorded occurrence of the USUV Africa 2 and Africa 3 genetic lineages in Poland.