IDO1 and Zika virus infectious disease: Since C57BL/6 mice are resistant to ZIKV infection (27, 34, 35), ZIKV infection was performed by intracerebral route by inoculation of with 1 x 106 PFU of ZIKV (i.c) in both WT C57BL/6 and IDO-1-/- mice (Figure 5A).