Bluetongue virus particle. Computer model of the crystalline structure of the core particle of the Bluetongue virus (BTV). The particle diameter is around 700 Angstroms. BTV is an orbivirus, and is of major economic importance as an insect-borne pathogen of cattle and other ruminants. It is named after the cyanotic (blue) tongue it causes in sheep. It is not transmitted to humans. The structural data was obtained from the diffraction pattern of synchrotron radiation (high energy X- rays from a particle accelerator) passing through crystals of the virus.