BSR cells were infected with BTV-1, BTV-8 or the corresponding deletion mutants at a MOI of 0.05 in 35 mm dishes. At 24 h post-infection, cells were fixed using cold 2.5% gluteraldehyde and 1% osmium tetroxide. Cells were subsequently pelleted through 1% SeaPlaque agarose (Flowgen), dehydrated using a graded alcohol series and embedded in Epon 812 resin, followed by cutting and analysis in a Joel 1200 EX II electron microscope.