Investigation of Powassan virus lineage II pathogenesis and neurotropism in mice

Abstract

Powassan virus (POWV) is an emerging tick-borne flavivirus that causes disease in humans. POWV has considerable genetic and phenotypic diversity, including highly variable replication in vitro and pathogenesis in mice. This study sought to define the extent of variability in pathogenesis within POWV lineage II in mice and investigate possible viral determinants. Relative to other strains, two New York-derived isolates, NY.19.12 and NY.19.32, caused earlier clinical signs and earlier detection of viral RNA (vRNA) in the spleen and brain compared to mice infected with virus derived from a lineage II infectious clone (WI.97.ic). Sequencing revealed these strains share three amino acid substitutions in envelope, NS1, and NS5 compared to other lineage II strains, which were engineered into a mutant infectious clone. At early time points post-infection, clinical signs, vRNA detection in the cerebellum, and viral distribution in the brain were similar between NY.19.12 and the mutant clone, suggesting these mutations may play a role in disease progression and early neuroinvasion. However, NY.19.12 vRNA was detected in the spleen at significantly higher rates compared to both WI.97.ic and the mutant clone, indicating factors other than these mutations are responsible for increased spleen infection. Importantly, this study highlights the complexity of POWV pathogenesis and suggests that POWV lineage II strains have varying disease phenotypes likely driven by multiple genetic differences. ImportanceTick-borne flaviviruses exhibit considerable genetic and phenotypic diversity in nature, influencing their transmission and pathogenesis. Defining the mechanisms of pathogenesis requires understanding how inter-strain variation translates to phenotypic differences in viral dissemination and neuroinvasion. This study demonstrates that even closely related Powassan virus (POWV) lineage II strains display distinct disease phenotypes that are only partially attributable to nonsynonymous consensus mutations within the viral coding sequence. By highlighting the complexity of POWV infection dynamics in mice, these findings provide valuable insights into how POWV lineage II diversity may shape disease progression and severity in humans.