CD81 and Zika virus infectious disease: These findings suggest that more CD81 molecules are expressed on the membranes of ZIKV-infected monocyte (~1.4-fold increase); this change could explain the formation of syncytia (refer to Figure S4A) and thus the efficient cell-to-cell ZIKV infection indicated by the high percentages of cells positive for the viral E and NS1 proteins (refer to Figure 1).