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Viral Disease - Blue Tongue

Synonym

Catarrhal fever of sheep, Sore muzzle of sheep

Definition

Acute infectious disease of sheep characterized by fever, inflammation and ulceration of buccal mucosa and tongue. Edema of lungs and dependent parts.

Etiology

Arthropod-borne orbi virus in the family of Reoviridae

Incidence

The disease was first recognized in South Africa in 1902. It is now reported to occur worldwide in tropical, subtropical and temperate climates. Blue tongue is endemic in India. The recent incidence of blue tongue in sheep, cattle and buffaloes has increased manifold in our country.

Susceptibility

Sheep are primarily affected

Goat, cattle and deer are also susceptible to infection

Transmission

Biting insect of the genus of the Culicoides

It can be transmitted by semen from an infected bull.

Pathogenesis

Virus entry into host - Affecting the blood vessels and causes- hyperemia, edema & hemorrhage.

Initial replication in hematopoietic cells then viremia occurs

Subsequent replication in endothelial cells

Swelling in endothelial cells (Degeneration and necrosis)

Edema, hemorrhage, thrombosis and infarction

By Affecting hemopoietic tissue - Anemia and leucopenia results

Clinical signs

High fever with reddening of nasal and oral mucosa

Dyspnea and salivation

Watery discharge from the nostrils, mucous dry and form crusts

Gross lesions

Edema of lips, nose, ear and inter mandibular space "edema and cyanosis of Tongue "- 'Blue Tongue'

Later petechiae appears on the oral and nasal mucosa

Gangrene occurs

When fever subsides- flushing of feet- warm and reddened

CORONET- hemorrhage at the junction of skin and hoof

Epithelium shed- leaving excoriation and bleeding points

Fever (Subsides) - pain occurs around the coronary band of feet - lameness

Spread through Respiratory and Digestive tract - Pneumonia along with gastroenteritis occurs -emaciation - prostration - muscular weakness.

Haemorrhages may be found on the mucosa of abomasum and intestine as well as in the myocardium

Sero-sanguineous fluid in the pericardial sac

Liver revealed fatty changes

Spleen- congestion and swelling .Death is due to Pneumonia

Pathognomonic Lesions

Haemorrhages at the base of the pulmonary artery and aorta.

Microscopic lesions

Loss of striation & hyalinization of musculature.

Diagnosis

Symptoms

Gross lesion

Egg inoculation and inoculation into lambs

Virus neutralization test

Differential diagnosis

Foot-and-mouth disease

Epizootic hemorrhagic disease

Contagious ecthyma

Sheep pox.

Treatment

Local irrigations with mild disinfectant solutions may afford some relief. Affected sheep should be housed and protected from weather, particularly hot sun, and fluid and electrolyte therapy and treatment to control secondary infection may be desirable.

Control

Reduction of infection through vector abatement Attempts to control bluetongue through a reduction of infection consists of reducing the risk of exposure to infected Culicoides and reduction in Culicoides numbers.

Neither are particularly effective. Reducing the risk of exposure is attempted by spraying cattle and sheep with repellents and insecticides and housing sheep at night.

Biweekly application of pennethrin was found not to be effective in preventing infection.

During transmission periods avoidance of low, marshy areas or moving sheep to higher altitudes may reduce risk. Because of the preference of some Culicoides for cattle as a host, cattle have been run in close proximity to sheep to act as vector decoys.

Widespread spraying for Culicoides control is not usually practical and has only a short-term effect.

There is a high mortality in Culicoides that fed on cattle that have been treated with a standard anthelmintic dose of ivermectin and also a larvicidal effect in manure passed for the next 28 d for Culicoides that breed in dung.


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