Characterization of H5N1 high pathogenicity avian influenza virus belonging to clade 2.3.4.4b isolated from Ezo red fox in Japan in a mouse model

Abstract

The H5N1 avian influenza virus has caused severe disease in birds worldwide and is now spreading to mammals, including humans. In 2022, this virus was detected for the first time in an Ezo red fox in Japan. To understand its potential impact on mammals, we studied this virus in mice and found that it caused severe illness, spreading to multiple organs, including the lungs and brain. Surprisingly, despite lacking genetic mutations typically associated with mammalian adaptation, the virus was highly virulent in mice. This finding suggests that the H5N1 virus may pose a greater threat to mammals, including humans, than previously thought. Given their continued spread among wild and domestic animals, our findings underscore the urgent need to monitor how recent H5N1 viruses behave in mammals.