FIG. 3.

Positive effect of adaptive mutations on BDV growth in cell culture. Kinetics of virus spread was determined in Vero cells (A) and MEF from IFNAR1^0/0 mice (B). Cultures were infected with the various recombinant viruses at a multiplicity of infection of 0.01 per cell. At the indicated times, the percentages of virus-infected cells were determined by analyzing samples of the cultures by indirect immunofluorescence. Growth curves of BDV-PK and wild-type BDV in IFNAR1^0/0 MEF were stopped on day 34 as no virus-infected cells were detected in these cultures.