Introduction/Causative Agent:
Bluetongue is caused by a virus that can infect both sheep and goats. However, most goats do not show the severe clinical signs that are common with sheep infections. This disease is found throughout the world, with some countries being bluetongue-free (Canada, New Zealand, and many northern European nations).Clinical Signs: At first, the animal may have a fever (temp > 105° F) and swelling of the face, lips, muzzle, and ears. The gums (mucosa) of the mouth are often red and occasionally the tongue is blue (cyanotic). Affected animals salivate excessively and may have some discharge out of the nose. As the problem progresses, ulcers and erosions develop in the mouth. The virus can also cause respiratory problems (pneumonia-like), lameness, abortions, and birth defects. The bluetongue infections common to the United States cause death in only a small percentage of cases (0-30%). Goats rarely show clinical signs of disease. Other diseases that look like bluetongue include photosensitization, soremouth, and foot-and-mouth disease.
Disease Transmission:
This disease is transmitted from animal to animal by insect bites. Insect vectors of the genus Culicoides (no-seeums, biting midges, sandflies, or gnats) are the most common. The other means of spreading this disease, through semen and from mother to offspring during pregnancy, are less common.Diagnosis:
To precisely (definitively) diagnose bluetongue as the cause of disease, the virus should be isolated from blood and tissue samples taken from adult animals or aborted fetuses. Other serological (blood) tests are also available (enzyme linked immunosorbent assay-ELISA and polymerase chain reaction-PCR) that can help diagnose bluetongue.Treatment:
There is no specific treatment for bluetongue. All efforts for infected animals should focus on keeping the animal comfortable and preventing secondary bacterial infections with the use of antibiotics. Animals with mouth lesions should be fed soft feeds or gruels. Feed, water, and shade should be close at hand.Prevention:
Prevention can focus on attempting to reduce exposure to biting insects. This is accomplished by housing animals indoors during peak insect activity times (morning and early evening) and by eliminating breeding areas for the insects. These breeding areas include low lying grazing areas where water tends to pool, over-flowing troughs, and muddy, swampy land. Vaccines are also available, but are used only in problem areas and flocks/herds. Because some vaccines can cause abortions and fetal defects, the vaccine should be used before the breeding season. Current vaccines are not completely protective for all strains of the bluetongue virus.