African horse sickness is a highly infectious and deadly disease caused by the African horse sickness virus. It commonly affects horses (mortality rate 70-90%), mules, and donkeys. Zebras and donkeys rarely develop serious symptoms.

How do horses contract the disease?

AHS does not spread directly from one horse to another but is transmitted by the Culicoides midge ( also called “punkies” or “no-see-ums” ), which becomes infected when feeding on other infected Equidae. Mosquitoes and biting flies may also be able to transfer the virus.

Blood-feeding Culicoides Midges

It occurs mostly in the warm, rainy season when midges are plentiful, and disappears after frost when the midges die. Most animals become infected in the period associated with sunset and sunrise when the midges are most active.


The disease manifests in three ways, namely the lung form, the heart form and the mixed form. The lung (dunkop) form is characterised in the following manner:

  • very high fever (up to 41 degrees).
  • difficulty in breathing, with mouth open and head hanging down.
  • frothy discharge may pour from the nose.
  • sudden onset of death.
  • very high death rate (90%).

This form of the disease has the highest mortality rate. (90%)

The heart (dikkop) form is characterised in the following manner:

  • fever, followed by swelling of the head and eyes.
  • in severe cases, the entire head swells (“dikkop”).
  • loss of ability to swallow and possible colic symptoms may occur.
  • terminal signs include bleeding (of pinpoint size) in the membranes of the mouth and eyes.
  • Slower onset of death, occurring 4 to 8 days after the fever has started.

Mortality rate is between 50 and 70%, and survivors recover in 7 days

The mixed form is characterised by symptoms of both the dunkop and dikkop forms of the disease.

Diagnosis and Notification

The symptoms described above may assist with an initial diagnosis of AHS. This diagnosis can only be confirmed by identifying the virus in a laboratory. It is, therefore, essential that blood samples be taken from the horse during the fever stage of the disease for analysis. As AHS is a controlled disease, horse owners are obliged by law to notify the local State Veterinarian of suspected cases.

There is no specific treatment for animals with AHS apart from rest and good husbandry. Complicating and secondary infections should be treated appropriately during recovery. 

Control of African Horse Sickness

African Horse Sickness (AHS) is one of a number of diseases known to be potentially damaging to the livestock economy. By way of the Animal Diseases Act (Act No. 35 of 1984), AHS has been declared a state-controlled disease, thereby empowering the state to implement measures to control the disease. Horse owners are also required by this law to notify their local state veterinarian of any cases of AHS. The Act also requires that all equines (horses, donkeys and mules) must be vaccinated at least once a year with an approved AHS vaccine.

How can I protect my animals from African horse sickness?

The best way to protect animals from African horse sickness is to make sure they get their annual vaccinations, as well as to decrease their exposure to biting midges and other insects (e.g., mosquitoes and biting flies). Stabling horses in insect-proof housing, particularly between dusk and dawn when the insects are most active, can help prevent exposure. Insect repellents and insecticides may also be useful. Monitor your horse’s temperature. Horses with fevers should be examined by your veterinarian.

African Horse Sickness Vaccination Programme

All horses and all foals should be vaccinated against African Horse Sickness by a veterinary surgeon, using a registered, non-expired vaccine supplied by the Veterinarian administering the vaccine.

Foals between the ages of 6 and 18 months should get two sets of vaccines not less than 30 days apart, where possible, between 1 June and 31 October; and thereafter every year between 1 June and 31 October.

Contact us if you have any questions and any of our friendly vets will assist.