This disease is caused both by bluetongue virus and epizootic hemorrhagic disease virus, with the results of infection referred to collectively as hemorrhagic disease. These are similar orbiviruses in the family Reoviridae, and exist as many strains that differ in pathogenicity. Biting midges (Diptera: Certatopogonidae) of the genus Culicoides are the only known vectors of this disease, though many different species are involved around the world.
The name ‘ bluetongue ’ is based on the tendency of the tongue and mucosal membranes to turn blue, a result of cyanosis. This also can occur with epizootic hemorrhagic disease infection. Other common signs of infection include an arched back, lameness, and painful or cracked hooves in affected animals. Affected animals can appear disoriented, weak and staggering, or asymptomatic but followed by sudden death. Death may result from congestion of the lungs, necrosis, and internal hemorrhaging. The digestive tract and the organs are typically involved, including the kidneys, thymus, spleen, and lymph nodes. Reproduction is also affected, resulting in aborted or stillborn animals, particularly livestock. Because the viruses can be transmitted in semen, mandatory testing of semen is required prior to artifi cial insemination. Thus, economic loss results from the disease in livestock, the inability to export semen to countries that lack the disease, and from reduced abundance of wildlife.
Hemorrhagic disease affects wild and domestic ruminants in many parts of the world, including temperate and tropical areas. In the USA, disease is most prevalent in the western and southeastern states. Cattle and sheep are especially susceptible to infection, especially in North America. Most sheep and cattle remain asymptomatic, however. Hemorrhagic virus is reported to cause clinical disease in such North American species as white - tailed deer, Odocoileus virginianus ; pronghorn, Antilocapra americana ; bighorn sheep, Ovis canadensis ; elk, Cervus elaphus ; mountain goat, Oreamnos americanus ; and American bison, Bison bison . Hemorrhagic disease is particularly lethal to white - tailed deer and pronghorn. Though much less of a problem thus far, many African species seem to be susceptible to infection, including greater kudu, Tragelaphus strepsiceros ; muntjac, Muntiacus reevsi ; Grant ’ s gazelle, Gazella granti ; gemsbok, Oryx gazella ; sable antelope, Hippostragus niger ; African buffalo, Syncerus caffer ; ibex, Capra ibex ; and others. Antibodies to bluetongue virus have been found in carnivores in Africa, including wild dog, Lycaon pictus ; lion, Panthera leo ; cheetah, Acinonyx jubatus ; spotted hyena, Crocuta crocuta ; and others. It is possible that these carnivorous animals were infected by preying on infected ungulates.
