UDG-complementing cells (CAN20 cells) (Figure 4A) or DF-1 fibroblasts (Figure 4B) were infected with MVAΔudg isolates vDG013, vDG014, or with (udg+) MVA-gz at a virus/cell ratio of 3, and virus yields were determined by plaque assay on CAN20 cells at the indicated times following infection. The gene discussed is UNG; the disease is infection.