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==Description==

==Description==

Bluetongue is a non-contagious, arthropod-borne disease of ruminants, caused by bluetongue virus (BTV). The virus has been isolated from hosts worldwide (excluding Antartica)¹, despite being initially recognised in Africa in the late 19th and early 20th centuries². Although BTV's transmission and epidemiology is dependent on insect vectors, bluetongue greatly influences the global trade of ruminants as it is an Office International des Epizooties List A-classified diseases³.  

Bluetongue is a non-contagious, arthropod-borne disease of ruminants, caused by bluetongue virus (BTV). Sheep are particularly badly affected, and often suffer a cyanotic tongue which lends the disease its name. The virus has been isolated from hosts worldwide (excluding Antartica)¹, despite being initially recognised in Africa in the late 19th and early 20th centuries². Although BTV's transmission and epidemiology is dependent on insect vectors, bluetongue greatly influences the global trade of ruminants as it is included on the Office International des Epizooties List A of animal diseases³. Originally thought to be a disease of tropical and sub-tropical regions, bluetongue has shown a propensity to become established in temperate areas, and in recent years has spread North, through the Mediterranean Basin, to become endemic in many European countries including the UK.

 

Because BTV infection of ruminants is not contagious, the global distribution of BTV coincides with the distribution of competent Culicoides insect vectors.  As a direct consequence of its inclusion in the OIE List A, BT continues to impact the global trade of ruminants and their germplasm [2]. Furthermore, BTV recently emerged throughout much of the Mediterranean Basin to precipitate the largest and most economically devastating epidemic of BT ever described in Europe, and the virus currently is endemic in substantial portions of Italy, Greece, the Balkans, and adjacent countries. The incursion of BTV into southern Europe has had a devastating impact on livestock production in the region (especially in Italy) because of severe disease and remarkably high mortality in sheep, and restrictions of the movement of domestic livestock [5]. To address the growing international impact of BT, the OIE and the European Union recently sponsored the Third International Symposium on Bluetongue that was held in October, 2003, in Taormina, Sicily (www.bluetonguesymposium.it/index.htm).

 

BT was first described as "Malarial Catarrhal Fever" and "Epizootic Catarrh of Sheep" in the original written descriptions of the disease by investigators in South Africa. The name of "bluetongue" was later used to describe the distinctive cyanotic tongue of some severely affected sheep. The first descriptions of BT were published in the late 19th and early 20th century, although farmers in South Africa recognized the disease soon after the introduction of European breeds of sheep to that region of the world [32]. Prior to the 1940s, BT was thought to be confined to southern Africa and the first well - documented epizootic of BT outside of Africa occurred amongst sheep on Cyprus in 1943. The disease was recognized in Texas soon thereafter, and an extensive epizootic occurred on the Iberian Peninsula in 1956 - 57. The disease subsequently was recognized in the Middle East, Asia, and in southern Europe. These epizootics were interpreted in the middle of the 20th century to reflect the emergence of BT disease from its presumed ancestral origin in Africa, leading to "doomsday" scenarios regarding putative global spread of BT that justified its inclusion in OIE List A. It now is clearly evident that BTV infection occurs throughout tropical and subtropical regions of the world, extending also into many temperate regions as well. BT disease, however, is either rare or non-existent in many regions with endemic BTV infection. Furthermore, it is clearly apparent that the global spread of BTV was not a recent event, and that different serotypes and strains of BTV have evolved in different regions of the world, coincident with the presence of distinct species of Culicoides insect vectors

==Aetiology==

==Aetiology==