African horse sickness (AHS)

About African horse sickness

African horse sickness (AHS) is a serious viral disease that affects horses and other equids, including donkeys, mules and zebras. It does not affect humans.

The disease spreads through bites from infected midges (Culicoides species). It is not spread by direct contact between animals.

AHS is one of the most serious diseases of horses. The mortality rate in horses is 70-95%, mules around 50%, and donkeys around 10%. Infection in zebra and African donkeys is often undetected.

Zebras can carry the virus for up to 40 days with little or no sign of disease. Donkeys are also relatively resistant.

AHS can appear in different forms in horses:

• Pulmonary form — the most severe form. Causes breathing difficulty and can lead to death within hours, with a mortality rate of up to 90%.
• Cardiac form — causes swelling of the head, neck and eyelids, with fever and reddened eyes. Mortality rate of up to 50%.
• Mixed form — the most common, with signs of both forms above. Mortality rate of up to 70%.
• Horse sickness fever — a mild form, rarely fatal. More often seen in donkeys and partially immune animals.

The incubation period can range from 2 to 14 days.

Clinical signs alone are not sufficient to confirm ASF. Laboratory testing is required.

African horse sickness in Australia

Australia has never had African horse sickness (AHS). Keeping it out is a national priority.

Australia’s AHS‑free status supports trade in horses and equine genetics. An outbreak would have serious impacts on the horse industry.

If AHS were detected in Australia, it would likely lead to

• immediate quarantine and movement controls on affected and exposed animals
• suspension of exports to countries that require AHS-free certification
• intensive vector control to prevent further midge-borne spread.

Australia’s response policy is to eradicate AHS as quickly as possible.

How to report African horse sickness

African horse sickness is a nationally notifiable animal disease. If you suspect AHS in any equid in Australia, report it immediately to:

• your private veterinarian
• your state or territory agriculture department
• the Emergency Animal Disease Hotline on 1800 675 888.

Do not wait for a diagnosis. AHS can look like other equine diseases, including anthrax, equine infectious anaemia, equine viral arteritis and Hendra virus.

African horse sickness overseas

AHS is endemic in sub-Saharan Africa, where it circulates in zebra populations and causes periodic outbreaks in horses.

The disease has occasionally spread outside of Africa. Most recently, outbreaks occurred in Thailand and Malaysia in 2020. Both were successfully eradicated.

AHS has never been detected in the Americas, eastern Asia or Australasia. However, changes in midge distribution driven by climate change are widening the global risk zone, including parts of South-East Asia and the Asia-Pacific region.

Information for horse owners and industry

If an AHS incursion happened in Australia, it would have serious impacts on Australia’s horse industry. Good biosecurity and early reporting help protect your animals and the broader industry.

• Know the signs and report early — If you see unusual illness or sudden death, report it immediately.
• Manage exposure to midges — stable horses at night where possible and reduce exposure at dawn and dusk when midges are most active.
• Use insect control — use repellents, screens or insect‑proof housing where practical.
• Manage animal movements — be cautious when introducing new horses or animals that may have come from overseas.
• Follow import requirements — only import equids from AHS-free countries through official channels that meet Australian biosecurity requirements.

AUSVETPLAN resources

AUSVETPLAN contains the nationally agreed approach for responding to emergency animal disease incidents in Australia. The following documents are relevant to an AHS response.

Additional resources