To determine the influences of PEDV replication on intracellular ROS level, Vero cells were infected with PEDV for various periods of time, and a fluorescence probe, DCFH-DA, was added to the medium prior 15 min to use a flow cytometry. As shown in Figure 2A and 2B, exposure to PEDV resulted in increased ROS production which began at 2 h post-infection and peaked at 6 h (Figure 2A and 2B) .