Isolation and Identification of Circulating Serotypes of African Horse Sickness Virus in Ethiopia

An outbreak of African Horse Sickness (AHS) in Ethiopia was investigated in order to isolate and identify circulating serotypes of African Horse Sickness Virus in Ethiopian equines between July and September 2003. Six hundred and fifty (650) equines of different species (horse, donkey, mule) were examined. Viral specimens were collected from 12 acutely sick and moribund animals. Clinical and necropsy findings distinguished two forms of the disease: a peracute pulmonary form and a subacute cardiac form. Laboratory investigation of tissue and whole blood specimens collected from sick and moribund animals identified two different serotypes of AHS viruses: serotype 9 and serotype 6. The identification of serotype 6 represents the first report of this serotype in Ethiopia. Vol. 3, No. 1 • The Journal of Applied Research in Veterinary Medicine 40 immunization of susceptible hosts with suitable vaccines. The absence of cross protection among different serotypes, however, necessitates incorporation of available serotypes into the vaccines utilized. In 2002–2003 Ethiopia faced serious and repeated outbreaks of AHS in different regions, including southern, western, central, and northern Ethiopia. The outbreak affected horses vaccinated with monovalent vaccines containing type 9 AHSV (AHS Vaccine, National Veterinary Institute, Debre Zeit, Ethiopia). It is well documented that in spite of its wide distribution, serotype 9 of AHSV has a lower virulence than other serotypes, killing few horses in enzootic areas. The outbreak encountered in 2002–2003, however, resulted in high mortality. Donkeys, which were thought to be resistant to AHS, were observed to encounter clinical AHS in the Tgrai region of northern Ethiopia. Considering the diversity of AHSV serotypes and the absence of cross-protection, it has been strongly recommended that polyvalent vaccines be used. However, the absence of previous research on serotype identification in Ethiopia has made it difficult for vaccine manufacturers to shift to polyvalent vaccines. The objective of this study was, therefore, to isolate and identify the circulating AHSV serotypes in Ethiopia. MATERIALS AND METHODS Study Area and Animals The study was conducted in selected areas of Ethiopia where the 2002–2003 outbreaks of AHS were reported, including Southern Ethiopia (Awassa, Hossana, Wondogenet, and Hagereselam); Western Ethiopia (Jimma, Bedelle, Nekemte, Horroguduru, and Chaliya) and Central Ethiopia (Debre Zeit, Meki, Zeway, Filtimo, and Bekejo). Within each of these outbreak regions, areas (villages) with high incidence of epidemics and risk areas were selected for study. Six hundred and fifty (650) equine species (horses, mules, and donkeys) reared in the selected areas were closely examined and sampled irrespective of age and sex.