Abstract
Bluetongue (BT) is a non-contagious, infectious, arthropod transmitted viral disease of domestic and wild ruminants that is caused by the bluetongue virus (BTV), the prototype member of the Orbivirus genus in the family Reoviridae. Bluetongue was first described in South Africa, where it has probably been endemic in wild ruminants since antiquity. Since its discovery BT has had a major impact on sheep breeders in the country and has therefore been a key focus of research at the Onderstepoort Veterinary Research Institute in Pretoria, South Africa. Several key discoveries were made at this Institute, including the demonstration that the aetiological agent of BT was a dsRNA virus that is transmitted by Culicoides midges and that multiple BTV serotypes circulate in nature. It is currently recognized that BT is endemic throughout most of South Africa and 22 of the 26 known serotypes have been detected in the region. Multiple serotypes circulate each vector season with the occurrence of different serotypes depending largely on herd-immunity. Indigenous sheep breeds, cattle and wild ruminants are frequently infected but rarely demonstrate clinical signs, whereas improved European sheep breeds are most susceptible. The immunization of susceptible sheep remains the most effective and practical control measure against BT. In order to protect sheep against multiple circulating serotypes, three pentavalent attenuated vaccines have been developed. Despite the proven efficacy of these vaccines in protecting sheep against the disease, several disadvantages are associated with their use in the field.
Highlights
Bluetongue (BT) is a non-contagious, infectious, arthropod transmitted viral disease of ruminant and camelid species which is caused by the bluetongue virus (BTV), the prototype member of the Orbivirus genus in the family Reoviridae [1]
This study indicated that a wide range of African carnivores can be infected with the virus
Due to the subclinical nature of BT in the majority of infected sheep, as well as the availability of effective attenuated vaccines, BT is thought to be of less importance today by veterinary authorities than other livestock diseases that are present in South Africa
Summary
Bluetongue (BT) is a non-contagious, infectious, arthropod transmitted viral disease of ruminant and camelid species which is caused by the bluetongue virus (BTV), the prototype member of the Orbivirus genus in the family Reoviridae [1]. Theiler introduced the first vaccine against BT that consisted of a single virus strain (BTV-4) that was attenuated by serial passage in sheep This crude blood vaccine induced remarkable cross-protection to other serotypes and was used by sheep farmers in South Africa for over 40 years [48,49]. A sero-prevalence survey for BTV-specific antibodies was conducted amongst Merino sheep in the high-lying regions of the Eastern Cape, where sheep are not vaccinated since BT disease is not recognized This survey indicated that a large proportion of Merino sheep that were bled in early spring and autumn tested positive for antibodies against the virus. The endemicity of BTV in South Africa as well as the wide availability of vector competent midge species has made South Africa an attractive destination for international scientists that are interested in conducting Culicoides oral susceptibility studies
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