SOME EPIDEMIOLOGIC AND ECONOMIC-ASPECTS OF A BLUETONGUE-LIKE DISEASE IN CATTLE IN SOUTH-AFRICA - 1995 96 AND 1997/

In December 1995 to March 1996 and the early summer of 1997 South Afri ca experienced above average rainfall which favoured the occurrence of Culicoides transmitted diseases. During this period several outbreaks of an uncommon disease of cattle occurred over a large part of the co untry. The clinical signs were similar to those of infection with the viruses of bluetongue (BT) and epizootic haemorrhagic disease of deer (EHD). Virus isolation from cattle and Culicoides yielded both viruses . Dual infections occurred on several farms. Typing of BT isolates yie lded types 2, 3, 6 and 8. On at least two farms more than one BT virus serotype was involved. On one farm only EHD virus could be isolated f rom cattle and Culicoides. Serological tests confirmed that on this fa rm the disease was caused by EHD. In 1932/33, when a similar disease w as reported conditions were vastly different. Rainfall figures show th at the 1932/33 season was exceptionally dry. Techniques available at t hat time could not identify EHD and the cause was reported to be BT. T he occurrence of BT in a dry season and over a much wider area than th e distribution in South Africa of Culicoides imicola, the only proven vector for BT, is a clear indication that other species less dependent on high rainfall are involved. The present isolation of BT virus from three of five pools of parous C. bolitinos is evidence that this spec ies, which breeds in cattle dung, may be an additional vector for BT.