CPT-Tert cells were plated in 24-well plates and treated for 20 h with 1000 AVU/ml of IFNT or UIFN and then infected with either BTV-1 or BTV-8 at different MOIs (0.1, 0.01 and 0.001). The medium was replaced 2 h after infection and the cells maintained in the presence of either IFNT or UIFN at the original concentration. At 72 h post-infection, the cells were washed once with phosphate buffered saline (PBS; pH 7.4) and stained for 16 h using a 0.5% crystal violet/10% formaldehyde solution. We used Image-Pro Plus (MediaCybernetics), in order to quantify in each well the percentage of the monolayer that was disrupted after BTV replication. Results were expressed as the percentage of destroyed monolayer by calculating for each well the following formula: (number of pixels above background: total number of pixels times) X 100.