The PRRSV Ch-1a strain, the vaccinia virus WR strain, and the Akabane virus OBE-1 strain were part of our laboratory collection. The former was propagated in Marc-145 cells, and the latter two were propagated in BHK-21 cells, respectively, and these two cell lines were cultured in DMEM (Invitrogen) supplemented with 10% of fetal calf serum (FCS, Invitrogen) in a humidified 37°C, 5% CO 2 incubator.