Electron microscopic evidence for bridges between bovine respiratory syncytial virus particles

Electron microscopic examination of ultrathin sections of a continuous cell line of ovine kidney (OK) origin, infected by bovine respiratory syncytial virus (BRSV), revealed the presence of well defined bridges between virus particles. This is the first report of this novel structure. Observation of ultrathin sections of human RSV Long strain also grown on OK cells did not show inter-particle bridges and therefore suggested that this structure could be specific to BRSV. The biological significance of these bridges is not clear at this time; a possibility is that the bridges are formed by the fusion protein of BRSV which is known to cause cell fusion. Besides the structural implications, the importance is in relation to purification strategies for this virus, which must now take into account that most of the viral particles occur in large aggregates.