African horse sickness (AHS) is a life threatening disease of equids caused by African horse sickness virus (AHSV), a member of the genus Orbivirus in the family Reoviridae. The virus is transmitted to horses by midges (Culicoides spp.) and the disease is most prevalent during the time of year, and in areas where the Culicoides spp. are most abundant, namely in late summer in the summer rainfall areas of the country. Whilst the clinical signs and presentation of the disease were well documented by Sir Arnold Theiler (1921), very little is known or documented about AHSV dynamics or the clinical pathological and serological responses of horses to natural infection with AHSV. This dissertation describes the history and current knowledge on AHS, and the methods and results of a prospective study on natural AHSV infection of horses, undertaken between 2009 and 2010 by the Equine Research Centre (ERC) at the University of Pretoria, Faculty of Veterinary Science, Onderstepoort. This study is the first documented study of its nature and included animals of various ages and therefore variable vaccination status. The objectives of the study were to describe the viral dynamics of AHSV infection in horses, to gain a better understanding of the clinical pathological and serological responses to natural AHS infection and to demonstrate early detection of AHS infection in horses under field conditions. / Dissertation (MSc)--University of Pretoria, 2010. / Veterinary Tropical Diseases / unrestricted