Treating IBV with S. nigra extracts prior to infection is necessary for full virus inhibition and works synergistically with treating cells after infection. Cells and virus were treated with 4.0 x 10-3 g/ml of S. nigra extract as indicated below. Infection was done at an MOI of 0.1. Quantitation of virus titers at 24 h p.i. was done by plaquing in duplicate using neutral red staining. Independent infections with IBV were performed three times, with two replicates per assay.