An ICP0- virus is avirulent in scid mice. A. Scid mice were inoculated with 2 × 105 pfu per eye of the ICP0- virus n212 (n = 6 mice). The mean ± sem of the logarithm of viral titers recovered from mouse eyes is plotted over time (open black symbols). The survival of n212-infected scid mice is plotted over time (red line). On day 70 p.i., n212-infected scid mice were challenged with 2 × 105 pfu per eye of wild-type HSV-1 strain KOS (subsequent viral titers are shown as open blue symbols). The dashed line indicates the lower limit of detection of the plaque assay used to determine viral titers. B. Survival of BALB/c mice versus scid mice infected with KOS or n212. Bars represent the mean ± sem of survival frequency of ICP0- virus-infected mice at day 60 p.i. (n = 5 experiments; Σn = 30 mice per group).