The ZH501 strain of wt RVFV was obtained from the Special Pathogens Branch at the Centers for Disease Control and Prevention (CDC) (Atlanta, Georgia). RVFV ZH501 was originally isolated from a patient during the 1977 outbreak of RVFV in Egypt by inoculating the human specimen into suckling mice brain. After amplification of the virus in the suckling mice brain one more time, the ZH501 virus stock was generated after two passages in FRhL cells and two passages in VeroE6 cells. The Vero cell line and MRC-5 cell line were used for a viral plaque assay as described previously [44] . All of the experiments that used virulent ZH501 were performed in The Robert E. Shope, MD BSL-4 Laboratory in the John Sealy Pavilion for Infectious Diseases Research at The University of Texas Medical Branch at Galveston, Texas.