La Crosse virus reassortants highlight genomic determinants of infection and pathogenesis

Abstract

The genomic determinants that contribute to orthobunyavirus infection and pathogenesis are not well-defined. In this study, we harnessed the process of reassortment to understand which viral factors drive change in the replication and pathogenesis of La Crosse virus (LACV). We systematically reassorted the genomic segments of two genetically similar Lineage I LACV isolates into six unique reassortants. Despite the parental isolates having high levels of RNA and protein consensus, the reassortants demonstrate how minimal changes in RNA and protein structure can have significant changes in viral growth and reproduction in vitro in mammalian and insect models. We observed that swapping the S segment between isolates led to differences in replication and assembly resulting in one non-rescuable reassortant and one viable reassortant that exhibited an increase in viral growth dynamics. Switching the M segment led to changes in viral plaque phenotype and growth kinetics. L segment reassortants similarly differed in changes in viral growth dynamics. We further explored the M segment reassortants in a neonate mouse model and observed a role for the M segment in neuroinflammation and virulence. Through reassortment of the La Crosse virus genomic segments, we are able to further understand how genomic determinants of infection and pathogenesis operate in orthobunyaviruses. Future investigations will focus on identifying the specific molecular elements that govern the observed phenotypes in vitro and in vivo.