Genetic Characterization of Avian Influenza Virus A (H1N1) Isolated from a Fieldfare Turdus pilaris in Ukraine

Avian influenza viruses are predominantly associated with waterfowl and shorebirds, and are rarely detected in other avian hosts in nature. In 2021, an H1N1 virus was isolated from a Fieldfare Turdus pilaris in Zaporizhzhia Oblast, Ukraine. A phylogenetic analysis revealed that all eight gene segments belonged to the Eurasian low-pathogenic avian influenza lineages. The highest nucleotide identity of the HA gene was observed with viruses detected in Georgia, Sweden, and Ukraine (99.11%), while the NA gene showed the greatest identity to viruses from Western Europe (99.14–99.57%). Genetic analysis of the HA cleavage site showed a sequence (PSIQSR↓GLF) that contained a single basic amino acid. No deletions were detected in the stalk region of NA gene, and no specific mutations in PB2 protein were found. However, several amino acid substitutions were identified in the HA gene (D204E, S207T, and D239G) that may affect the binding affinity to specific antibodies. The occurrence of this virus in a wild, seemingly healthy thrush indicate that additional surveillance in poorly studied ecological groups such as Passeriformes is warranted.