Skip to content

African Horse Sickness

Related Links

if you've seen a term you don't understand, please check here for an explanation.
Tell us if you want any of the documents on this page in an alternative format.

African Horse Sickness (AHS) is a fatal disease that affects horses, mules, donkeys and zebras and is a notifiable disease.

AHS is a disease that is spread by midges. Dogs have been known to be infected by eating infected horsemeat. It has never occurred in the UK, but is found in Southern Africa.

The spread of disease is influenced by climatic conditions including warm, moist weather and high rainfall, which favour the spread of carrier insects (such as midges) as well as spread by wind dispersal.

Signs of the disease

The clinical signs seen are dependent upon what form of the disease is present:

  • in the most acute form, which has a short incubation period of only 3 to 5 days, affected horses have a high fever, severely laboured breathing, coughing and profuse discharge from the nostrils. The mortality rate is very high, with up to 95% of horses dying within a week
  • in the cardiac form of the disease, which has an incubation period of from 7 to 14 days, swellings are present over the head and eyelids, lips, cheeks and under the jaw. The mortality rate is around 60% and death results from heart failure
  • the mixed form of the disease is a combination of the above 2 types. It has an incubation period of from 5 to 7 days and the disease shows itself initially by mild respiratory signs followed by the typical swellings of the cardiac form
  • horse sickness fever is the mildest form, characterised by a fever with low temperatures in the morning rising to a high peak in the afternoon.

If you suspect signs of any of AHS you must immediately notify your local Animal and Plant Health Agency (external link).


No vaccine for AHS is currently licensed in the European Union (EU). Use of a modified live vaccine for AHS (such as the one being produced by Onderstepoort Biological Products Ltd in South Africa) carries a risk of vaccine virus reversion to wild type. This means that the virus used in the vaccine could potentially undergo changes whereby it could actually infect the carrier insects and, subsequently, susceptible horses. Currently the vaccine will not be considered for use in the UK other than in an emergency situation.


The African Horse Sickness (Wales) Regulations 2013 (external link) will only be used during an outbreak or suspected outbreak of AHS. The risk of an AHS outbreak in Great Britain is considered to be low. However, recent outbreaks of Bluetongue and Schmallenberg have demonstrated the risk posed by animal diseases spread by Cullicoides midges. Similar regulations are already in force in England and Scotland.  

The African Horse Sickness: Disease Control Strategy for Great Britain (external link) outlines how an outbreak of AHS in Great Britain would be managed. 

Document Download