BHK-21 (American type cell culture collection) were grown at 37uC under 5% CO2 in Glasgow's minimum essential medium (GMEM), supplemented with 10% foetal bovine serum, 10% tryptose phosphate broth, penicillin G (100 IU/ml) and streptomycin (100 mg/ml). Culicoides sonorensis KC cells were grown at 28uC in Schneider's insect medium supplemented with 15% fetal bovine serum.