BTV-8 infected KC or BHK-21 cells and GIV infected BHK-21 cells all contain NS4, as revealed by western blot analyses and confocal microscopy, confirming the existence of a new and previously un-described protein, encoded by ORFx of orbivirus Seg-9. NS4 has not previously been detected in purified BTV virus or core particles [20] . Western blot analyses of purified BTV-8 particles confirmed that the protein is 'non-structural'.