Bluetongue is an infectious, noncontagious, arthropod-borne viral disease of sheep and goats. Bluetongue is caused by bluetongue virus (BTV), which is a non-enveloped, RNA orbivirus of the Reoviridae family. There are over 26 distinct serotypes of the bluetongue virus.
Bluetongue disease was first reported in 1870, when European sheep were imported into South Africa. It occurs throughout the world in sporadic outbreaks, when immunologically naive ruminants are introduced to an epizootic zone, which includes temperate areas where outbreaks occur seasonally. Outbreaks generally occur when vector populations (Culicoides spp) are at their highest, which is late summer in temperate regions, and year-round in tropical and subtropical regions. Culicoides feed mostly at dusk and early evening so animals should be removed from pastures at these times