Fig. 2.

Clinical signs of USUV infection in suckling immunocompetent mice according to strains. a Survival rates of neonatal Swiss mice (6 days old) intraperitoneally inoculated with 10³ TCID50/mouse of six different USUV lineages. CT = control mice. b Onset date of symptoms in USUV-infected suckling mice. Mice were monitored daily until clinical signs of disease were displayed and then were euthanized. Symptoms appeared at around 5 dpi for all strains excepted for AF3 (9 dpi). Epilepsy is observed only in mice infected by EU2. n = 6 for each group. c Viral burden in blood and brain was measured by RT-qPCR assay at 6 dpi and indicated by TCID50 equivalent per mL or per gram. d Transverse sections of the brain (cerebellum) of USUV-infected mice at 6 dpi showing the presence of viral antigen after pan-flavivirus staining (associated with luxol blue). *p < 0.05 and **p < 0.01