Genetic characterization of bovine rhinitis A and B viruses in Japan and evidence of viral RNA amplification in primary bovine respiratory epithelial cells.

The aphthoviruses bovine rhinitis A virus (BRAV) and bovine rhinitis B virus (BRBV) can be detected in bovine respiratory specimens. However, information regarding Japanese strains and genome-scale data remains limited. To address this gap, we screened Japanese bovine nasal swab specimens for BRAV and BRBV using reverse transcription-quantitative polymerase chain reaction and subjected positive specimens to genome sequencing. Among 98 specimens from cattle admitted to Azabu University, BRAV and BRBV were detected in 8 each using a cycle threshold (Ct) cutoff ≤35. Near-complete genome sequences were obtained from four BRAV-positive specimens and one BRBV-positive specimen. Phylogenetic analyses revealed that four BRAV strains belonged to a BRAV1-related lineage distinct from the Japanese BRAV2 strain H-1. In contrast, BRBV/25IKH5 clustered with LAV/238002 within the BRBV-1 group. To evaluate viral RNA amplification after passage, specimens with low Ct values that tested positive for BRAV or BRBV alone were inoculated onto Madin-Darby bovine kidney (MDBK) cells and primary bovine respiratory epithelial cells. RNA from BRAV/LAV/238037 and BRBV/25IKH5 was detected in culture supernatants of primary bovine respiratory epithelial cells but not in those of MDBK cells, and there was no apparent cytopathic effect. Following passage in primary cells, mean Ct values decreased from 37.0 to 23.9 for BRAV/LAV/238037 and from 30.7 to 22.7 for BRBV/25IKH5 at 72 hr after inoculation. This study expands genome-scale information on bovine rhinitis viruses and presents evidence of BRAV and BRBV RNA amplification after passage in primary cells.