Japanese Encephalitis Virus and ISchizophyllum commune/I Co-Infection in a Harbor Seal in Japan

Japanese encephalitis virus (JEV) infections in seals are limited, with only two cases reported. Here, we report a case of meningoencephalitis and bronchopneumonia caused by the co-infection of JEV and Schizophyllum commune in a dead seal (Phoca vitulina) housed in an aquarium in Japan. The JEV isolate from the seal was classified as genotype GIb based on E gene sequences, which included recent Japanese human and mosquito isolates. The Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, has a wide host range, extending from pigs and ardeid birds to opportunistic dead-end hosts, such as humans and horses. However, JEV encephalitis infections in aquatic mammals are rare, with only two cases in seals reported to date. Here, we report a lethal case of JEV and Schizophyllum commune co-infection in an aquarium-housed harbor seal in Japan. We isolated JEV from the brain of the dead seal and characterized its phylogeny and pathogenicity in mice. The virus isolate from the seal was classified as genotype GIb, which aligns with recent Japanese human and mosquito isolates as well as other seal viruses detected in China and Korea, and does not exhibit a unique sequence trait distinct from that of human and mosquito strains. We demonstrated that the seal isolate is pathogenic to mice and causes neuronal symptoms. These data suggest that seals should be considered a susceptible dead-end host for circulating JEV in natural settings.