Veterinaria Italiana, 45 (2), 265‐274 © IZS A&M 2009 www.izs.it/vet_italiana Vol. 45 (2), Vet Ital 265 African horse sickness: a description of outbreaks in Namibia Massimo Scacchia (1) , Rossella Lelli (1) , Agostino Peccio (1) , Tiberio Di Mattia (1) , Rosa Stella Mbulu (2) , Anna Laure Hager (2) , Federica Monaco (1) , Giovanni Savini (1) & Attilio Pini (1) Summary African horse sickness is a vector‐transmitted viral disease that affects equidae. The authors report cases of disease that occurred in Namibia between 2006 and 2008. These were recorded by staff of the Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise ‘G. Caporale’ and the Central Veterinary Laboratory in Windhoek. All cases described were confirmed by laboratory testing. This study received the support of Namibian state and private veterinarians and horse breeders. Keywords African horse sickness, Culicoides, Horse, Equid, Namibia, Virus. Introduction African horse sickness (AHS) is a viral disease of equidae that is endemic in sub‐Saharan Africa. Cases of the disease have been reported in North Africa where seroconversion still occurs in Morocco, in the Iberian Peninsula and areas of middle‐eastern Asia. As is the case for bluetongue, the aetiological agent is a RNA virus of the genus Orbivirus, family Reoviridae. It is transmitted by arthropod vectors that belong to various species of Culicoides. Nine serotypes have been identified to date (2). The disease is often fatal in horses and mules, and is characterised by signs and pathological disorders caused by respiratory and cardiovascular impairment. The literature on infectious diseases describes four clinical forms, namely: pulmonary, cardiac, mixed and febrile. Clinical signs and lesions can be pathognomonic (2, 6, 9). However, laboratory confirmation of a suspected outbreak is required to identify the serotype responsible for the outbreak. AHS must be differentiated from other diseases, such as purpura haemorrhagica, viral arteritis and babesiosis (2, 8). In Southern Africa, particular attention must be paid to equine encephalosis, caused by a virus from the same genus and family as the AHS virus. Encephalosis virus causes signs similar to a mild form of AHS (Fig. 1) but it also affects the central nervous system (3, 10). In contrast with AHS, mortality is low and does not exceed 5%. It is often confirmed by retrospective diagnostic serology. In Namibia, AHS vaccination is performed using a live attenuated vaccine produced by Onderstepoort Biological Products in Onderstepoort, South Africa. The vaccine contains seven of the nine viral serotypes and is administered in two separate doses 21 days apart. The first dose consists of three serotypes and the second of four serotypes. Serotypes 5 and 9 are not included, the former because it was found to be insufficiently attenuated and the latter because it is considered that serotype 6 protects against serotype 9. (1) Istituto Zo o p ro fila ttic o Sp e rim e nta le d e ll’ Ab ruzzo e d e l Mo lise ‘ G . C a p o ra le ’ , Via C a m p o Bo a rio , 64100 Te ra m o , Ita ly m .sc a c c hia @ izs.it (2) C e ntra l Ve te rina ry La b o ra to ry, 24 G o e the Stre e t, P. Ba g 13187, Wind ho e k, Na m ib ia