Blue tongue

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. Oedema of lungs and dependent parts.

Aetiology

  • Arthropod-borne orbi virus in the family of Reoviridae

Incidence

  • The disease was first recognized in South Africa in 1902.
  • It is now reported 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 mani fold in our country

Susceptibility

  • Most animal species are highly susceptible
  • Goat, cattle and deer are also susceptible to infection

Transmission

  • Biting insect of the genus of the Culicoides
  • It has been transmitted by semen from an infected bull

Pathogenesis

Affecting the blood vessels – Hyperemia, oedema & Haemorrhage.

  • Virus entry into host
  • Initial replication in haematopoietic cells
  • Viremia
  • Subsquent replication in endothelial cells
  • Swelling in endothelial cells ( Degeneration and necrosis)
  • Oedema,haemorrhage
  • Thrombosis and infarction
  • Affecting haemopoietic tissue – Anaemia and leucopenia results

Clinical signs

  • High fever with reddening of nasal and oral mucosa
  • Dyspnoea and salivation
  • Watery discharge from the nostrils , mucous dry and form crusts
  • Tongue appears bluish or cyanotic and swollen

Gross lesions

  • Oedema of lips, nose, ear and inter mandibular space "Oedema 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 - haemorrhage at the junction of skin and hoof -Lameness 
  • Epithelium of hooves 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
  • Serosanguineous fluid in the pericardial sac
  • Liver -Fatty change
  • Spleen- congestion and swelling
  • Death may be due to Pneumonia because of secondary bacterial infection

Pathognomonic Lesions – Haemorrhages at the base of the pulmonary artery and aorta

Microscopic lesions

  • Loss of striationa & hyalinization of musculature
  • Haemorrhages , oedema and necrosis are seen in affected organs

Diagnosis

  • Symptoms - Blue tongue and coronet haemorrhages
  • Gross lesion -Haemorrhages at the base of the pulmonary artery and aorta
  • Egg inoculation and inoculation into lambs for virus isolation and characterization
  • Virus neutralization test
Last modified: Saturday, 3 December 2011, 5:36 AM