A nanoluciferase-tagged Schmallenberg virus (SBV): an efficient tool for measuring and tracking viral infection dynamics

<b>Introduction.</b> Schmallenberg virus (SBV) is an arthropod-borne virus and belongs to the Simbu serogroup within the family <i>Peribunyaviridae</i>, genus <i>Orthobunyavirus</i>. Infection of naïve ruminants at critical stages of gestation can result in severe congenital malformations or abortion.<b>Gap statement.</b> Tools to measure virus infection parameters in cell culture such as replication efficiency, as well as neutralization assays, are mainly available in the form of assays based on the evaluation of cytopathic effects. The methods are labour-intensive and low-throughput, as they require long incubation periods of several days. Tools such as tagged SBV that allow for fast and automated readout are missing.<b>Aim.</b> We aimed to develop a tagged SBV that can be used for assays with fast and automated read-out.<b>Methodology.</b> We report the construction of a recombinant SBV stably expressing the nanoluciferase (nluc) enzyme (rSBV_nluc). Using reverse genetics, the nluc gene was integrated into the genome of an SBV variant naturally harbouring a large deletion within the Gc-head domain. The nluc gene was inserted into this locus.<b>Results.</b> The nluc-tagged virus showed <i>in vitro</i> no signs of attenuation and identical replication properties when compared to the parental virus in baby hamster kidney (BHK-21) cells. Our results demonstrate a new approach for rapid access to SBV replication. By performing nluc assays, we were able to track viral replication and also virus uptake in detail. We further evaluated neutralization properties of an SBV variant, which is lacking a major part of its antigenic domain (Gc-head) and developed a nanoluciferase activity-based serum neutralization assay.<b>Conclusion.</b> Overall, the nluc-tagged SBV is a suitable tool that further facilitates the study of viral infection dynamics and allows for high-throughput assays.