African Horse Sickness (AHS) is a notifiable seasonal virus infection of odd-toed ungulates, causing peracute and acute disease predominantly in equids. The etiologic agent is a double-stranded RNA virus (African Horse Sickness Virus, AHSV) in the Orbivirus genus (family Reoviridae). Upon first introduction of the virus into a previously free region, lethality in infected horses can be as high as 95%, significantly impacting local economies. Disease is most severe in horses, but only mild in horse/donkey hybrids and donkeys. Dogs can develop disease after ingesting infected horseflesh.
Even though clinical symptoms usually are pathognomonic, laboratory confirmation is essential to avoid confusing AHS with other equine diseases (equine encephalitides, equine viral arteritis). AHSV antigen or antibodies can be detected in the laboratory. In endemic areas (mostly in Africa) AHSV is transmitted by hematophagous Culicoides midges. Indigenous European midge species are also assumed to be suitable vectors for AHSV. To prepare for an AHS outbreak, the European Union has created a vaccine bank.