The route of introduction of the strain of BTV-8 that has recently caused such devastation in many countries across Europe remains unknown. Five of the BTV serotypes (1, 2, 4, 9, 16) initially invaded the Mediterranean basin by extension from adjacent regions of either North Africa or the Middle East and of these five serotypes only BTV serotype 1 (BTV-1) has since spread to Northern Europe. These viruses have caused substantial economic losses through mortality and reduced productivity of affected animals resulting in the requirement for mass vaccination of susceptible livestock and very expensive restrictions on the movement and trade of animals from affected regions. Until recently, only transient incursions of single serotypes of BTV had occurred in Europe but, since 1998, at least eight different serotypes of BTV have emerged and persisted in Europe. In recent years the distribution of BTV in Europe has changed considerably. Bluetongue disease (BT) also occurs in cattle infected with some strains, such as the BTV-8 strain currently circulating in Northern and Western Europe. The virus can infect most species of domestic and wild ruminants although the clinical signs are most common in sheep and some species of deer.
There are currently 24 recognized serotypes of BTV worldwide.
Bluetongue virus (BTV) is an arthropod-borne pathogen that is transmitted almost exclusively by the bites of Culicoides midges, which act as vectors for the virus between its ruminant hosts.
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