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Blue tongue is a viral disease of sheep and other ruminants that is caused by a virus transmitted by insects. Today, 25 serological types of the blue tongue virus are known in the world. To date, 9 types of virus have been diagnosed in Israel. The name of the disease is derived from one of the symptoms caused by the virus in sheep.

Infection

Under field conditions the bluetongue virus is transmitted between sheep and cattle, in goats natural infection is rarer. Cattle is usually used as a carrier and culture site for the virus before infecting sheep. Cattle is more attractive to the species of insects (gnats) that serve as biological transmitters of the virus and therefore, are a leading carrier of the virus.

Sensitivity to the disease

All breeds of sheep are susceptible to the disease, but it varies from breed to breed. European breeds and marino are very susceptible to the disease, and infection may end in death. African breeds are relatively resistant to the disease, usually showing only mild feverish disease. In addition, sensitivity differs between different ages, between different individuals from the same species and even from the same herd.

Disease Characteristics

After the virus penetrates the skin, it multiplies in the draining lymph nodes, and spreads with the help of the mononuclear cells to secondary proliferation sites in the lymph tissue and lungs. The virulence is usually detected on the third day. The peak is accompanied by high fever and occurs 6-7 days after infection. Changes are manifested by edema, congestion, bleeding, inflammation, necrosis.

Symptoms

The disease is characterized by high fever (40.5° - 42°C), prominent edema in the head area, bleeding in the oral cavity and carriages, muscle inflammation, and sensitivity to light. The duration of the disease depends on the severity of the clinical signs, in mild cases the disease is quick, in severe cases the disease will cause mortality within a week of infection.

Clinical Markers

• During incubation period - no clinical markers.
• After incubation period - rise of boty temperature (40.5° - 42°C).
• 48 hours after the increase in body temperature, mucus and secretions from the nose appear, accompanied by redness in the mucous membranes of the nose and mouth. There may be blood stains in the discharge from the nose after which salivation becomes foamy. In addition, the secretion causes scabs in the nostrils, which makes it difficult to breathe. The rate of respiration increases and the sheep breathes with its mouth open.
• Edema - Edema develops on the lips, face, eyelids and ears. May progress to other places like chest and neck. In acute cases where there is edema in the lungs, there is a noticeable difficulty breathing and foam coming out of the nose.
• Ulcers - Ulcers may develop on the gums and tongue and in the area of ​​the incisors. Also in the area of ​​the molars. They cause bad breath.
• The pain that develops as a result of the ulcers causes a lot of movement of the lips and tongue and as a result the formation of bloody foam and the smearing of water and food on the lips to a state of difficulty in swallowing.
• Hyperemia - hyperemia with spot bleeds on the papillae at the tip of the tongue. The tongue swells and becomes puffy and therefore protrudes from the mouth. Hyperemia in lip tissue may progress to the entire face and entire body. Broad dermatitis develops. A few weeks later brreaks in the wool can be noticed which may cause the wool to fall out.
• Leg defects - At first the hyperemia appears in the horn area, then there is bleeding under the thin horn, at the border between the skin and the horn of the hoof - which then appears as a prominent line of red to black bleeding. The bleeding causes a lot of pain and as a result the sheep will refuse to walk, and/or walk on their knees.
• In further aggravation a separation of the horn may be formed which creates a clear crack on the hoof.
• Eye inflammation - Another sign is eye inflammation. Inflammation is manifested by the secretion of tears from the eyes.
• Rotated neck - If the virus affects the skeletal muscles, in some sheep there will be a phenomenon of a twisted neckto one side.