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Disease factsheet: African Horse Sickness

If you suspect signs of any notifiable disease, you must immediately notify a Defra Divisional Veterinary Manager.

Commission Decision of 18 December 2008 establishing Community reserves of vaccines against African Horse Sickness

On 18 December 2008 the EU Commission published its decision (2009/3/EC) to make arrangements for the purchase of 100,000 doses of monovalent attenuated live vaccine against African Horse Sickness of each of the serotypes 1, 2, 3, 4, 6, 7 and 8. The contract for 2009-10 will be with Onderstepoort Biological Products Ltd (OBP) in South Africa for the supply, storage and delivery of the vaccines. The arrangements shall include the supply and storage of the vaccines and the shipment of the specified vaccines to the European Union, or an epidemiologically relevant direct neighbours, designated in case of emergency by the Commission.

Defra are supportive of this initiative and recognises that whilst the Qualitative Risk Assessment on African Horse Sickness (PDF) published in November 2008 assesses the risk of incursion of the disease into the UK as very low, the impact should it occur, could be significant.  

No vaccine for AHS is currently licenced in the EU. Use of a modified live vaccine for AHS (such as the one being produced by OBP) carries a risk of vaccine virus reversion to wild type (i.e. the virus used in the vaccine can potentially undergo changes that mean it could actually infect vectors, and subsequently susceptible equidae). Thus at the present time, the vaccine will not be considered for use in the UK other than in an emergency situation. The establishment of a central EU vaccine bank is supported by Defra as it ensures that a limited supply of vaccine is available for use should the need arise. The use of such vaccines will always be carefully considered on a risk-assessed basis.

Working in partnership to provide a central EU vaccine bank is a cost effective way of providing this extra assurance and will encourage the pharmaceutical industry to develop vaccines capable of being used in Europe.

14 September 2007 - International Trade - Preliminary Outbreak Assessment: African Horse Sickness (AHS serotype 2) in Senegal.

Background

African horse sickness is a highly fatal and infectious disease, which affects horses, mules and donkeys. It is caused by an orbivirus, and there are nine strains of the virus. The disease is not directly contagious between horses, and is present (endemic) in sub-Saharan Africa. The disease has spread as far north as morocco and the Middle East. Zebras and elephants may be infected without showing signs of disease. Dogs can also be severely infected by the virus, usually by eating infected horsemeat.

Recent outbreaks in Spain were probably related to imports of infected zebras from Africa.

Transmission

The spread of disease is influenced by climatic conditions which favour the spread of carrier insects (vectors) including warm, moist weather and high rainfall, as well as spread by wind dispersal. It is likely that the virus persists (overwinters) in other, unknown species in Africa when the insect is not active. This explains why the disease does not persist in other countries following an outbreak.

Clinical signs

The clinical signs seen are different depending on 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.

Post mortem

Blood samples from up to five horses showing high temperatures can be taken to diagnose this disease. These vary with the form of the disease. - from severe and extensive fluid in the lungs, including froth in the airway, to petecial haemorrhages in the heart and gut and hydropericardium in the cardiac form.

Equine Housing Vector Protection

Housing horses in accommodation at times of peak midge activity will reduce the likelihood of midge attack but it is unlikely to fully protect your horse against African horse sickness (AHS). A combination of protection measures is recommended to ensure the highest possible degree of protection is achieved. Further details on these protection measures (PDF 36KB) are available.

African horse sickness leaflets

GB Legislation

African Horse sickness is included in The Specified Diseases (Notification and Slaughter) Order 1992 to implement the slaughter requirements of EU Council Directive 92/35/EEC which lays down control rules and measures to combat African horse sickness.(1) Imported horses from at-risk countries outside the European Union are routinely tested for African horse sickness.

The severity of disease and the controls to monitor and restrict movement of horses could significantly affect the Equine Industry in the United Kingdom, particularly in southern UK, where this disease is most likely to occur.

EU Legislation

Council Directive 92/35 provides for compulsory notification, and the setting up of a protection zone of least 100 kilometres radius around and infected premises. This, together with a surveillance zone of at least a further 50 kilometres, would have to remain in force for at least 12 months.

(1) Official Journal of the European Community: No. L157, 10.6.92 p.19).

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Page last modified: March 31, 2009

Department for Environment, Food and Rural Affairs