Huh7 and SW13 cells were propagated in Dulbecco’s modified Eagle’s medium with Earle’s salts (Corning), both medias were supplemented with 10% fetal bovine serum (FBS; Gibco), 1% penicillin/streptomycin (Gibco), 1% sodium pyruvate (Sigma-Aldrich), 1% l-glutamine (HyClone), and 1% Hepes (Gibco). Minimally passaged CCHFV strain Afg09-2990 (39) or strain IbAr 10200 (USAMRIID collection) were used for all experiments, as indicated. Strain Afg09-2990 was previously passaged three times in Vero cells and then propagated at USAMRIID two times in Huh7 cells. Strain IbAr 10200 was passaged, as previously described (25). The viruses were collected from clarified cell culture supernatants and stored at −80°C. All CCHFV work was handled in biosafety level 4 (BSL-4) containment at USAMRIID.