Inhibitors (Methyl-b-cyclodextrin, cytochalasin-D or latrunculin-A) were added to cells for 0.5 h before infection. The cells were then inoculated with BTV-1 (as described above) also in the presence of an inhibitor. Mock-treated cells were infected in the absence of an inhibitor. After the 1 h incubation with virus, the cells were washed with GMEM to remove unbound virus and returned to 37uC in cell culture medium with reduced (2%) FBS, and supplemented further with 25 mM ammonium chloride. To control for any effects on intracellular virus replication the inhibitors were also added to other cells immediately after the virus inoculums were removed and coincident with the addition of ammonium chloride.