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African horse sickness in South East Asia

Two new African horse sickness (AHS) outbreaks have occurred in Thailand, affecting horses and zebras, according to a report issued by the World Organisation for Animal Health (OIE) on 14 October 2020.

The outbreak of African horse sickness (AHS) in Thailand was first reported in March 2020, and was the first time AHS had occurred outside the African region in 30 years. Thailand has now associated the outbreak with the importation of zebras from South Africa.

  • Thailand commenced vaccinating horses against AHS in mid-April, using an attenuated live polyvalent vaccine from South Africa.
  • Between April and July 2020, Thailand reported no new cases of AHS.
  • The new cases of AHS in Thailand were diagnosed in August (horses) and September (zebras).
  • In early September 2020, AHS was also diagnosed in five horses in Malaysia. According to Malaysian reports to the OIE, the affected horses were destroyed and no further cases have been reported.
  • The AHS virus is transmitted by biting Culicoides midges that feed on horses, and therefore the spread of the virus can difficult to control where such midges are abundant.

AHA is conducting 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 outbreaks in South East Asia 

More information


Page reviewed: 16/10/2020