Although filoviruses can replicate in various tissues and cell types, the molecular mechanisms of their broad tropism remain poorly understood (Figure 6) . By using an expression cloning strategy that has been used to identify several virus receptors, human folate receptor-α was first identified as a ubiquitous cellular cofactor that mediates infection by both MARV and ZEBOV (Chan et al., 2001) . This molecule is a glycosyl-phosphatidylinositollinked protein expressed on the cell-surface. However, a human immunodeficiency virus pseudotyped with EBOV GP could not www.frontiersin.org 