A review of African horse sickness and its implications for Ireland

African horse sickness (AHS) is a disease caused by the African horse sickness virus (AHSV). The disease affects horses, ponies, and European donkeys most severely; mules are somewhat less affected, and African donkeys and zebra are refractory to the devastating consequences of infection [1-4]. The virus is a non-contagious, vector-borne Orbivirus that is transmitted primarily by female Culicoides midges during a blood meal, which they require for reproduction [4]. In addition to equids, camels, goats, and buffalo can become infected [5]. Additionally, some carnivores such as dogs, can become infected via ingestion of contaminated meat. However, there have been no documented cases of transmission of AHSV in carnivores in the wild, and it is considered that they are a ‘dead-end’ host, rather than a reservoir of infection [6,7]. Owing to the potential of this virus to cause widespread death and debilitating disease in na？ve equid populations, it is listed as a notifiable equine disease by the World Organisation for Animal Health (OIE), which makes outbreaks of the disease compulsorily notifiable to the OIE. Such occurrences can result in serious consequences for international trade of animals and animal products for the affected country [8]. It is currently predicted, that a widespread outbreak of this disease would have a devastating effect on the horse industry of any country affected [9].The first recorded reference of AHS occurred in 1327 in Yemen [10], but it is most likely that the virus originated on the African continent where it could have been transmitted in the natural zebra population [2]. The disease was first recognised around 60 years after the initial introduction of horses to Africa in 1657, and the first major outbreak occurred in 1719. This outbreak resulted in the deaths of approximately 1, 700 animals [11]. Subsequently, there has been at least an additional 10 major (and several lesser) outbreaks of AHS on the African continent [2]. These outbrea