African horse sickness: are we prepared?

There have long been concerns that climate change and globalisation (particularly the transportation of animals and animal products) could lead to increased occurrence of exotic or novel vector-borne viral diseases within northern Europe. African horse sickness (AHS) is an infectious, noncontagious, insectborne viral disease of equids that is associated with mortality rates up to 95% in naïve populations [1]. A UK outbreak would therefore have devastating effects on animal welfare and major economic impacts on the equine industry.

What is the risk to the UK?

African horse sickness is endemic in sub-Saharan Africa, with short-lived outbreaks occurring in many parts of the world, although never further north than Spain. Midges of the genus Culicoides are the primary vectors of AHS and the geographical distribution of AHS is linked to the midge [2]. Historically, the risk to the UK was considered to be very low due to the lack of suitable species of midge; however, the 2007 outbreak of Bluetongue (BT) in the UK challenged this idea. BT virus is closely related to AHS virus and shares the same vector species of midges where both diseases are endemic. Before 2006, BT had never occurred in northern Europe, where the traditional vector species of midge are not present; however, it is now known that during the recent outbreak in northern Europe and the UK, indigenous midge species (particularly members of the Obsoletus and Pulicaris groups) were able to act as vectors [3]. Essentially, the concern is that the same could be true for AHS, if the virus were to be transported to northern Europe. Importantly, climate change may well affect both the distribution of different midge species and their inherent ability to transmit viruses [4]. Our preparedness for an outbreak of AHS is therefore dependent on prevention of viral importation (currently extremely unlikely via legal equid movement) and knowledge of the Culicoides epidemiology in the UK, particularly with regard to equine properties. […]