The bluetongue virus is spread by a type of small mosquitoes called midges. Bluetongue mainly affects sheep, but also cattle. The virus gives them a high fever, swelling and the characteristic blue tongue. About three-quarters of sheep that contract the disease do not survive.
In cattle, the disease manifests itself as fever, inflamed mucous membranes in the nose and mouth, sores on the udders and swelling of the legs. This can cause them to become lame, but they usually survive the disease.