The South African reference strain of BTV-1 (IAH reference number RSArrrr/01, ICTVdb isolate accession number 41010B4F) was grown on BHK cells and gradient purified according to previously published methods [49] . Purified virus was stored at 4uC in the presence of sodium-N-lauroylsarcosine (0.1%) to prevent virus aggregation and was used for all experiments [46, 49] . Viruses were diluted immediately before use thereby reducing the concentration of sodium-N-lauroylsarcosine to ,0.01% which showed no cytotoxic effects.