Evaluation of the effects of four antiviral mutagens on PRRSV replication. The effects of different concentrations of ribavirin (A), 5-fluorouracil (C), 5-azacytidine (E), and amiloride (G) in RPMI-1640 medium on the replication of the PRRSV isolate VR2332 in MARC-145 cells were evaluated, as determined by the production of progeny viruses (TCID50/ml) over time. Cytotoxicity assays were performed using cell culture fluids collected from MARC-145 cells every 12 hours after being incubated with the following mutagens: ribavirin (B), 5-fluorouracil (D), 5-azacytidine (F), and amiloride (H), as indicated in the panel. The results are expressed as the luminescence (RLU) from dead-cell protease activity. Asterisks represent a significant difference (p < 0.05) in virus replication after mutagen treatment compared to that after vehicle treatment.