Fig. 1.

Slow spread of plaques limits amplification of their infection signal. The infection signal (area of cell death) in a plaque expands linearly with time. If every virus particle released by an infected cell could always find a healthy host cell to infect, the signal would grow exponentially with time. Fluid flows across infected cells transport progeny virus particles to distant cells, creating an opportunity to amplify the infection signal. Curves are based on vesicular stomatitis virus infecting BHK cells: each cell is a disk with diameter 36 μm, infected cells produce 3,000 virus particles in 7 h, and plaques spread with radial velocities of 70 μm/h