African horse sickness (AHS) is a peracute, acute, subacute or mild infectious but non contagious disease of equids caused by African horse sickness virus (AHSV). The virus is classified in the genus Orbivirus of the family Reoviridae, of which there are nine serotypes, all transmitted by Culicoides midges. AHS is a World Organization for Animal Health (OIE) - listed disease and manifests pyrexia and clinical signs compatible with impaired respiratory and circulatory functions, characterized by oedema of subcutaneous and intermuscular tissues and of the lungs, transudation into the body cavities and haemorrhages on serosal surfaces. The mortality rate in horses, the most susceptible species, may be as high as 95 per cent, while mules are less susceptible and donkeys with rare exceptions only develop inapparent infections.