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African Horse Sickness

A widespread outbreak of African horse sickness (AHS) has been reported in Thailand, the first time AHS has occurred outside the African region in 30 years.

  • Thailand continues to provide weekly updates to the OIE on the AHS outbreak, which has now spread to twelve provinces and caused the death of almost 550 horses.
  • The diagnosis of AHS was confirmed by the Thai National Institute of Animal Health and by the OIE reference laboratory for AHS at Pirbright in the United Kingdom.
  • The source of introduction of AHS to Thailand is still under investigation, with media sources implicating imported zebras.
  • Thailand has commenced vaccinating horses in affected areas, using an attenuated live polyvalent vaccine from South Africa.

AHA has commenced a review of the AUSVETPLAN disease strategy for African horse sickness.

African horse sickness

  • African horse sickness (AHS) is the most serious known viral disease of horses, resulting in up to 80-90% mortality in affected horses.
  • The AHS virus (AHSV) is spread by midges of the Culicoides species that prefer to feed on horses.
  • Zebras are the natural reservoir hosts of AHSV in Africa, and they may carry the virus without showing any signs of disease.
  • Long distance spread of AHS can occur with the movement of live equids (horses, donkeys, mules, zebras), or infected insect vectors.
  • The last major outbreak of AHS outside of Africa occurred in Spain and Portugal in 1987-90, following the importation of wild African zebras.
  • The disease does not affect humans.

Control measures

Australia has strict import conditions on equids to prevent the entry of AHS (and other equine diseases) into Australia.

  • Control measures during an incursion are aimed at reducing horse contact with vectors and include:
    • housing horses under midge-proof netting
    • using insect repellants on horses
    • insecticides and other measures to reduce insect populations in the environment
    • preventing vectors feeding on infected horses.
  • An attenuated (weakened) live vaccine, available in Africa, will be used in Thailand to protect horses. The vaccine can be associated with severe side effects in some horses.
    • The vaccine is not available for use in Australia.

What to look for

Horses with AHS may show:

  • swelling of the face and eyelids, with reddened eyes
  • swelling of the brisket and front half of the horse
  • difficulty breathing, with or without frothy discharge from the nostrils
  • rapid deterioration and death.

Further information on the outbreak in Thailand

More information


Page reviewed: 02/06/2020