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African Horse Sickness

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African Horse Sickness is a highly fatal disease that affects horses, mules, donkeys and zebras and is a Notifiable Disease

Background to the disease

African Horse Sickness (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. An outbreak occurred in Spain relatively recently, which was associated with the import of infected zebras from 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.

Clinical signs

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 three to five 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 seven to fourteen days, swellings are present over the head and eyelids, lips, cheeks and under the jaw. The mortality rate is around 60 per cent and death results from heart failure
  • the mixed form of the disease is a combination of the above two types. It has an incubation period of from five to seven 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 African Horse Sickness 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.

African Horse Sickness (Wales) Regulations 2013

The African Horse Sickness (Wales) Regulations 2013 (external link) will only be used during an outbreak or suspected outbreak of African Horse Sickness (AHS).  The risk of an AHS outbreak in GB 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.  

African Horse Sickness:  Disease Control Strategy for Great Britain

This document outlines how an outbreak of African Horse Sickness (AHS) in Great Britain (GB) would be managed (external link).

African horse sickness: Question and answer

Commonly asked questions about African Horse Sickness.