Figure 1.

Evidence and proposed mechanism for nonlytic spread of a non-enveloped virus. (A) Top panel shows a single infected cell (1) infecting another cell (2) at 10 h after infection with a poliovirus variant that expresses DsRed. Transfer of infectious material from cell 1 to cell 2 occurs before the death of cell 1, shown by the penetration of Sytox Blue. The numbers of these nonlytic transfer events increase in the presence of autophagy stimulators loperamide or nicardipine. (B) Hypothesis for unconventional secretion of infectious viral material. Double-membraned vesicles induced by poliovirus infection contain virions and, most likely, unencapsidated viral RNA. Upon fusion of the outer membrane with the plasma membrane, the internal contents will be released. Depending upon the state of the inner membrane, the virions and viral RNA will be released free or inside a vesicle. Scale bar = 25 μm. This figure was modified from Fig. 4 published in Bird et al., PNAS 2014 111:13081 copyright National Academy of Sciences (USA).