African horse sickness (AHS) is a highly fatal, non-contagious, infectious disease, of horses, mules and donkeys caused by AHS virus.
This orbivirus is transmitted between hosts by small biting insects known as "midges" (Culicoides species). The clinical signs are usually more severe in horses than other equids and may vary depending on what form of the disease is present. Zebras may be infected with AHS virus but do not exhibit clinical signs. Carnivores such as dogs and big cats can also be infected with AHSV after eating infected meat, and AHSV antibodies have been found in elephants and rhinoceros, but the importance of these species for the transmission of AHSV remains unclear.
The virus exists as nine serotypes, all of which are endemic in sub-Saharan Africa. Outbreaks of AHS have occurred as far north as Spain and Portugal, and as far east as India and Pakistan but it has not persisted in these regions. Recent outbreaks of AHS in Spain and Portugal were probably related to imports of infected zebras from southern Africa.
The disease may be spread via the movement of infected equids but transmission is also promoted by climatic conditions which favour high populations of carrier insects (vectors). These insects can also be spread over long distances by wind dispersal.