Bluetongue is an insect-borne, viral disease affecting sheep, cattle, deer, goats, and camelids (camels, llamas, alpacas, guanaco, and vicu). Although sheep are most severely affected, cattle are the main mammal reservoir of the virus and are critical in disease epidemiology. The disease is non-contagious and is only transmitted by insect vectors (midges of the Culicoides species). The disease is caused by a virus belonging to the family Reoviridae. Bluetongue virus is a notifiable disease in many countries.
BTV affects sheep, cattle, deer, goats, and camelids (camels, llamas, alpacas, guanaco, and vicu. Humans are not affected.
Clinical signs are most apparent in sheep, where the disease is characterized by fever, widespread hemorrhages of the oral and nasal tissue, excessive salivation, and nasal discharge. In acute cases the lips and tongue become swollen and this swelling may extend below the lower jaw. Lameness, due to swelling of the cuticle above the hoofs, and emaciation, due to reduced feed consumption because of painfully inflamed mouths, may also be symptoms of this disease. The blue tongue that gives the disease its name occurs only in a small number of cases. The convalescence of surviving sheep is slow. The high fever in sheep results in wool breaks, which adds to production losses.
Goats, cattle, and wild ruminants such as deer can appear healthy when infected. This can lead to silent spread by midges feeding on the infected animals.