Résumé
Background: Usutu virus (USUV) is an emerging neurotropic arthropod-borne virus recently involved in massive dieoffs of wild birds predominantly reported in Europe. Although primarily asymptomatic or presenting mild clinicalsigns, humans infected by USUV can develop neuroinvasive pathologies (including encephalitis andmeningoencephalitis). Similar to other flaviviruses, such as West Nile virus, USUV is capable of reaching the centralnervous system. However, the neuropathogenesis of USUV is still poorly understood, and the virulence of thespecific USUV lineages is currently unknown. One of the major complexities of the study of USUV pathogenesis isthe presence of a great diversity of lineages circulating at the same time and in the same location.Methods: The aim of this work was to determine the neurovirulence of isolates from the six main lineagescirculating in Europe using mouse model and several neuronal cell lines (neurons, microglia, pericytes, brainendothelial cells, astrocytes, and in vitro Blood-Brain Barrier model).Results: Our results indicate that all strains are neurotropic but have different virulence profiles. The Europe 2 strain,previously described as being involved in several clinical cases, induced the shortest survival time and highestmortality in vivo and appeared to be more virulent and persistent in microglial, astrocytes, and brain endothelialcells, while also inducing an atypical cytopathic effect. Moreover, an amino acid substitution (D3425E) wasspecifically identified in the RNA-dependent RNA polymerase domain of the NS5 protein of this lineage.Conclusions: Altogether, these data show a broad neurotropism for USUV in the central nervous system withlineage-dependent virulence. Our results will help to better understand the biological and epidemiological diversityof USUV infection.