Recovery of recombinant infectious hematopoietic necrosis virus strain Sn1203 using the mammalian cell line BHK-21

Reverse genetics systems are powerful tools for understanding the virulence mechanisms and gene functions of negative-sense RNA viruses. The reverse genetics systems commonly used for recombinant infectious hematopoietic necrosis virus (IHNV) are based on vaccinia virus infection. To avoid the potential biological safety risks associated with vaccinia virus, a recombinant IHNV virus strain Sn1203 (rIHNV-Sn1203) was rescued in this study using a mammalian cell line, BHK-21. The genome sequence authenticity of rIHNV-Sn1203 was confirmed using two silent genetic tags introduced by site-directed mutagenesis. Indirect immunofluorescence assays and transmission electron microscopy revealed that rIHNV-Sn1203 and wild-type IHNV-Sn1203 (wtIHNV-Sn1203) had identical immunogenicity and virion morphology. The virulence and pathogenicity of rIHNV-Sn1203 were assessed in vitro and in vivo. Although rIHNV-Sn1203 displayed trends toward delayed intracellular viral replication and lower virion yields compared with wtIHNV-Sn1203, statistical analyses revealed no significant differences between these two viruses. Moreover, rainbow trout challenged with rIHNV-Sn1203 and wtIHNV-Sn1203 showed indistinguishable mortality. Together, these results show that IHNV was successfully rescued using BHK-21 cells. This method is very convenient and may also be suitable for use in the recovery of other Novirhabdoviruses.