Bluetongue (BT) is an infectious, viral and vector-borne disease of improved breeds of sheep and some species of deer that is of major international importance. The infection is usually unapparent in cattle, which acts as reservoir for the virus. However, some serotypes such as serotype 8 (BTV-8), which recently caused a severe epizootic of BT in northern Europe, exhibit a more important virulence in cattle.