Genetic diversity of Toscana virus glycoproteins affects the kinetics of virus entry and the infectivity of newly produced virions
Toscana virus (TOSV) is a pathogenic and transmissible Phlebovirus of the Bunyavirales order. Although TOSV is considered one of the leading causes of meningitis and encephalitis in humans during summer in the Mediterranean basin, its biology remains poorly characterized and neglected due to lack of tools to study the virus. To date, two principal genetic lineages (A and B) have been identified among TOSV-isolated strains based on phylogenetic analysis. The impact of TOSV genetic diversity on its biology is still unknown but highly relevant because it may influence the severity of the disease, viral tropism, and vaccine design. To address these questions, a reverse genetic approach based on two TOSV strains belonging to lineage A or B (i.e., TOSV-A and TOSV-B) and displaying different in vitro replicative fitness was used. Our results demonstrate that TOSV-A and TOSV-B have different Gn and Gc glycoproteins sequences which are responsible for the observed differences in terms of replicative fitness. Moreover, our data show that TOSV-A and TOSV-B display different entry kinetics and that newly-produced virions have different infectivity. This comparative approach allowed us to demonstrate that the genetic diversity of TOSV can significantly impact viral properties. This study highlights the need for a better molecular characterisation of the genome of circulating TOSV strains and, more specifically, of the viral Gn and Gc glycoproteins. Indeed, these proteins may strongly modulate viral pathogenicity and disease. Further work in this direction will provide important data to develop preventive strategies against this emerging pathogen taking into account TOSV glycoproteins genetic diversity. Authors SummaryToscana virus (TOSV) is a leading cause of aseptic brain infection in the Mediterranean basin during the summer. Despite the significant burden that TOSV represents to human health, the biology of this pathogen remains poorly understood and neglected. While distinct TOSV genetic lineages have been identified, the relationship between their genetic diversity and pathogenicity is still unclear. This point, however, is critical to understand the disease and design preventive strategies such as vaccines targeting circulating TOSV strains. Here, a reverse genetic approach was used to produce reassortant and chimeric viruses between two TOSV strains (referred to as TOSV-A and TOSV-B) belonging to the two main genetic lineages and displaying differential in vitro replication capacities. Our results show that the viral glycoproteins are key determinants in modulating TOSV replication. In addition, they demonstrate that viral entry and infectious viral particles production differ between TOSV-A and TOSV-B. This study provides the first evidence of differences in replication capacity between two genetically distinct TOSV viruses, and highlights the need for better molecular characterisation of circulating TOSV strains.