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Vet. Res.
Volume 35, Number 4, July-August 2004
Equine infectious diseases
Page(s) 445 - 466
How to cite this article Vet. Res. (2004) 445-466
Vet. Res. 35 (2004) 445-466
DOI: 10.1051/vetres:2004021

African horse sickness

Philip Scott Mellor and Christopher Hamblin

Institute for Animal Health, Department of Arbovirology, Pirbright Laboratory, Ash Rd., Pirbright, Woking, Surrey, GU24 0NF, United Kingdom

(Received 30 December 2003; accepted 1 March 2004)

Abstract - African horse sickness virus (AHSV) causes a non-contagious, infectious insect-borne disease of equids and is endemic in many areas of sub-Saharan Africa and possibly Yemen in the Arabian Peninsula. However, periodically the virus makes excursions beyond its endemic areas and has at times extended as far as India and Pakistan in the east and Spain and Portugal in the west. The vectors are certain species of Culicoides biting midge the most important of which is the Afro-Asiatic species C. imicola. This paper describes the effects that AHSV has on its equid hosts, aspects of its epidemiology, and present and future prospects for control. The distribution of AHSV seems to be governed by a number of factors including the efficiency of control measures, the presence or absence of a long term vertebrate reservoir and, most importantly, the prevalence and seasonal incidence of the major vector which is controlled by climate. However, with the advent of climate-change the major vector, C. imicola, has now significantly extended its range northwards to include much of Portugal, Spain, Italy and Greece and has even been recorded from southern Switzerland. Furthermore, in many of these new locations the insect is present and active throughout the entire year. With the related bluetongue virus, which utilises the same vector species of Culicoides this has, since 1998, precipitated the worst outbreaks of bluetongue disease ever recorded with the virus extending further north in Europe than ever before and apparently becoming endemic in that continent. The prospects for similar changes in the epidemiology and distribution of AHSV are discussed.

Key words: Culicoides / vectors / epidemiology / climate / disease prediction

Corresponding author: Philip Scott Mellor

© INRA, EDP Sciences 2004