African Horse Sickness

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  • 9 serotypes


  • Clinical: horses, mules, donkeys
  • Subclinical: african donkeys, zebras


  • Virus oscillates between horses and midges
    • Replicates in the salivary glands of biting midges, and occurs where they breed
  • Pantropic virus: infects endothelium and myocardium
  • Peracute: causes sudden death with pyrexia before the onset of clinical signs
  • Two forms:
    • Acute cardac-pneumonic form:
      • Interlobular pulmonary oedema
      • Pericarditis
      • Hemorrhage and oedema of the viscera
      • Death within 5 days
    • Subacute cardiac form:
      • Milder clinical signs but still a high mortality rate


  • Clinical signs
  • Differential: Equine Adinovirus
    • EAV causes oedema in the legs, which AHS does NOT
  • Suckling mouse inoculation
  • Virus serotype identification
  • Serology
  • RT-PCR will be used in future outbreaks


Control measures are largely preventative:

  • Slaughter or immediate isolation of sick animals
  • Mandatory and immediate vaccination with appropriate serotype
  • Restricted movement of susceptible animals
    • Protection zones and Surveillance zones set in place around outbreaks
  • Control of vector: ectoparasiticides, etc.

Current Relevance

  • Once only found in Africa, but since 1987 has recurred in Spain and Portugal
  • Not present currently in the UK but global warming may expand midge breeding grounds