African horse sickness virus

African horse sickness virus (AHSV) infects all equine species and is often fatal in horses and mules. It is from the family Reoviridae of the genus Orbivirus and there are 9 types (serotypes). AHSV is unenveloped and made up of a two layered capsid. The genome comprises 10 double stranded RNA segments. It can be spread through the blood and infects namely the lungs, spleen and other lymphoid tissues.

  • African horse sickness is a notifiable disease and should be reported.
    Please see the Defra website for advice on how to spot and report the disease.

Associated diseases:

AHS usually affects horses, donkeys, mules and zebras. Animals such as camels, African elephants and black and white rhinos may also be susceptible, but are unlikely to be involved in sustained transmission of the disease. Dogs can contract the virus through eating infected horse meat. AHSV can cause different forms of disease.

Clinical signs:

Respiratory form:

  • Fever
  • Breathing difficulties, coughing
  • Sweating 
  • Frothy discharge from the nostrils with death occurring within a few hours

Cardiac form:

  • Fever
  • Swelling around the eyes, lips, cheeks, tongue and neck
  • In some cases colic may also been seen

Mixed form:

  • A combination of signs from the cardiac and respiratory forms can be seen

Horse sickness fever:

  • Fever for a few days
  • Depression and reduced appetite
  • These animals often recover from the disease

Disease transmission:

AHS is spread by biting midges (Culicoides) and dogs can become infected by eating contaminated horse meat.

Disease prevalence:

AHS occurs primarily in Sub-Saharan Africa, but outbreaks have occurred in Egypt, the Middle East, Pakistan, India, Morocco, Spain and Portugal.

Impact for Society – what are we doing?

There is no specific treatment available other than supportive treatment and therefore measures to control exposure of horses to biting insects are essential to prevent an outbreak from spreading. A live attenuated vaccine is in use in Africa but it is not licensed in Europe, due to safety concerns.

The Pirbright Institute plays an important role in developing novel vaccines for viral diseases of livestock and is actively working on a promising vaccine candidate for AHS.


Downloadable factsheet

Research papers

Maan N S, Maan S, Belaganahalli M, Pullinger G, Montes A J A, Gasparini M R, Guimera M, Nomikou K, Mertens P P C (2015)

Journal of Virological Methods 213 , 118-126
de la Poza F, Marín-López A, Castillo-Olivares J, Calvo-Pinilla E, Ortego J (2015)

Virus Research 210 , 149-153
Gordon S J G, Bolwell C, Rogers C, Musuka G, Kelly P, Labuschagne K, Guthrie A J, Denison E, Mellor P S, Hamblin C (2015)

Onderstepoort Journal of Veterinary Research 82 (1) , e900
Baker T, Carpenter S, Gubbins S, Newton R, Lo Iacono G, Wood J, Harrup L (2015)

Parasites and Vectors 8 (1) , 604


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