Detection of antibodies against H5 subtype highly pathogenic avian influenza viruses in multiple raccoons in Tokachi District, Hokkaido, Japan, from 2022 to 2023

In recent years, infection cases of H5 subtype highly pathogenic avian influenza viruses (HPAIVs) in wild mammals have increased globally. To obtain recent epidemiological information regarding influenza A virus (IAV) infection in raccoons (Procyon lotor), the prevalence of anti-IAV antibodies in sera was analyzed among raccoons captured in Tokachi District, Hokkaido, Japan, from 2019 to 2023. Screening of serum samples using enzyme-linked immunosorbent assay and agar gel precipitation test detected anti-IAV antibodies in 5 of 114 (4.4 %) raccoons. All positive sera were from raccoons captured from 2022 to 2023. The hemagglutination inhibition test revealed that all five serum samples contained anti-H5 subtype HPAIV antibodies, and one also contained anti-H1 subtype antibodies. The neuraminidase inhibition test revealed that all five sera contained anti-N1 subtype antibodies, and one also contained anti-N8 subtype antibodies. In the virus neutralization test, these five sera showed stronger neutralization activity against the H5 subtype clade 2.3.4.4b HPAIV strain recently circulating worldwide compared to the old H5 HPAIV strain isolated in Japan in 2007. These findings suggested that raccoons could be involved in the circulation of H5 HPAIVs in nature.