Bluetongue Virus

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Antigenicity

  • 24 serotypes of BTV have been described

Hosts

  • Ruminants, including sheep, cattle, deer, goats, and camelids

Pathogenesis

  • Transfer occurs through blood from viremic animals via biting midges (Culicoides spp.)
  • Replication in haematopoietic and endothelial cells of blood vessels
  • Clinical signs vary between species, with sheep most severely affected
    • Pyrexia
    • Ocular and nasal discharge
    • Drooling from mouth uclers
    • Swelling of the mouth, head and neck
    • Lameness
    • Subdural hemorrhages
    • Inflammation of the coronary band
  • Cattle as the main reservoir
  • A blue tongue is rarely seen as as a clinical sign of infection
  • Resulting loss of condition, reduction in wool an meat production, which can be followed by death

Diagnosis

  • Clinical signs can be confirmed through the lab:
    • RT-PCR to detect viral RNA
    • ELISA serology for Ab and rising Ab titres

Current Relevance

  • August 2006: suspicious Dutch sheep confirmed as serotype 8
    • Serotype 8 found in Belgium, Luxembourg, Germany, and north-eastern France
    • Previously BTV-8 only seen in sub-Saharan Africa
  • August 2007: increased outbreaks in same regions
  • September 2007: first UK outbreak in Suffolk
  • 2008: Virus declared endemic and BTV-8 vaccine produced, voluntary vaccination strongly encouraged

Control

  • BTV is NOTIFIABLE
  • Vigilance in recognizing clinical signs
  • Restriction of movement:
    • Protection Zone: 100km radius around infected premises, movement within zone allowed but not in or out
      • Vaccination within PZ using appropriate serotype is encouraged but still voluntary
    • Surveillance Zone: 50km radius beyond PZ
  • Vector control: ectoparasiticides, etc.

Haemorrhagic Inflammation

  • Complete loss of integrity of epithelium. Uncommon.
  • Characteristic of Bluetongue Virus,
  • Epithelium lost and haemorrhage produces blue / black discoloration of the tongue, hence the name.