Young adult (<2 years, n = 5; blue) or aged female and male ferrets (>4 years, n = 5; red) were inoculated with 105.0 FFU/mL of each randomly selected SFTSV strain (A) B-3, (B) D, or (C) F. Survival, viral titers in serum, and platelet concentration were assessed. The normal range of platelets (171.7 × 103/μL to 1280.6 × 103/μL) is marked by dashed lines in each panel. Both viral titers and platelet concentrations are presented as mean ± SEM. Pound sign (#) indicates no sample due to death of all ferrets of this group. Asterisks (*) indicate statistically significant difference between infected young adult and aged infected ferrets per dpi as determined by Mantel-Cox method (survival) or 2-way ANOVA with Šidák’s comparison (viral copy number and platelets). Crosses (†) indicate significant difference in platelet count between noninfected aged adult and infected aged ferrets as calculated by 2-way ANOVA with Tukey’s test. *P < 0.05 and **P < 0.001, ††P < 0.001, ***P < 0.0001.