Cell cultures. The following cell lines were used in the antiviral tests: human foetal small intestine epithelial cells (H4) [25] (a generous gift from Dr. Tor Savidge, USA), pig small intestine epithelial cells (CLAB), isolated in our laboratory [26] and maintained by University of Maribor, Slovenia, and bovine calf small intestine epithelial cells (CIEB), isolated in our laboratory [26] and maintained by University of Maribor, Slovenia. The cells were grown in advanced Dulbecco's Modified Eagle's Medium (DMEM) (Sigma-Aldrich, Grand Island, USA), supplemented with 10% foetal calf serum (Cambrex, Verviers, Belgium), L-glutamine (2 mmol/L, Sigma), penicillin (100 units/mL, Sigma), and streptomycin (1 mg/mL, Fluka, Buchs, Switzerland). Cell lines were routinely grown in 25 cm 2 culture flasks (Corning, New York, USA) at 37 • C in a humidified atmosphere of 5% CO 2 and 95% air until confluent monolayers attained. Culture medium was changed routinely.