Relative body weight, temperature change, serum viral RNA copy number, and survival of aged ferrets infected with recombinant SFTS viruses. (A–D) Twelve ferrets in each group were inoculated with 4 × 106 PFUs of rHB29 (red), 4 × 106 PFUs of rHB29NSsP102A (blue), 5 × 105 PFUs of rHB2912aaNSs (green), or 5 × 105 PFUs of CB8/2016 (purple). Relative weight (A), temperature (B), viral RNA copy number in the serum (C), and survival (D) were assessed at the indicated times p.i., and mean values are shown ± SEM. The asterisks indicate significance compared to each day p.i. sample analyzed by one-way ANOVA with Dunnett multiple comparison test (A–C) or the 2-tailed Mantel–Cox method (D). *P = 0.0424, **P = 0.0023 and ***P < 0.0134 (A); *P = 0.0007, **P < 0.0001, ***P = 0.0113 and ****P = 0.0032 (B); *P = 0.0031, **P = 0.0192, ***P = 0.0214, ****P = 0.0378, *****P = 0.0001, and ******P < 0.0001, (C); and *P < 0.0001 (D). # Sample not tested as animals had died/been killed.