Oita virus rediscovered after 50 years: isolation of genetically conserved strains from bats in Southern Japan

Bats are natural reservoirs of numerous viruses, including members of the Rhabdoviridae family. Oita virus (OITV), classified within the genus Ledantevirus, was first isolated from the blood of a Japanese horseshoe bat (Rhinolophus cornutus) in the Oita Prefecture, Japan, in 1972. However, since then, no other OITV isolates have been reported. In this study, we isolated two OITV strains-OITV 321/2022 and OITV 326/2022-from oral swab samples of R. cornutus collected in the Katano Cave, Kagoshima Prefecture, Japan. Genetic analysis revealed >98% nucleotide identity with the previous isolate, OITV 296/1972. Phylogenetic analysis confirmed their classification within the Ledantevirus subgroup C. We assessed viral growth kinetics using 17 cell lines from diverse animal species, including bats, rodents, humans, and arthropods. OITV 321/2022 showed efficient replication in primate-derived, bat-derived, and human-derived cells, but not in tick or mosquito cell lines. Experimental infection of BALB/c mice demonstrated that OITV 321/2022 induced no overt clinical signs via either the intracerebral or intranasal routes. However, systemic infection and viral replication in the brain and lungs were observed by intracerebral inoculation. Intranasal inoculation with OITV 321/2022 and OITV 296/1972 resulted in transient pulmonary infection without systemic dissemination. This study provides evidence of OITV circulation in wild bat populations over 50 years, highlighting the need for continued surveillance of bat-associated rhabdoviruses in Japan.

Bats are known reservoirs of zoonotic viruses, and their proximity to humans raises concerns regarding zoonotic risks. We report the first isolation of the Oita virus (OITV), a bat-associated ledantevirus, that has circulated for over 50 years. Unlike a previous blood-derived isolate, our isolates were obtained from oral swabs, suggesting their potential for respiratory transmission. OITV could infect a wide range of mammalian cells, including human-derived cells, and induce systemic infection in mice without clinical symptoms. These findings indicate that OITV possesses a broad host tropism and may circulate among microbats through the respiratory tract. Although the pathogenicity of the newly isolated strain appears to be attenuated compared with that of a historical brain-passaged strain, its ability to replicate in human cells underscores its potential zoonotic relevance, necessitating active surveillance and functional characterization of bat-derived rhabdoviruses to better assess emerging infectious disease threats.