Bluetongue Virus

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.