The prevalence of different African horsesickness virus serotypes in the Onderstepoort area near Pretoria, during an outbreak of African horsesickness in South Africa in 1995/1996

During 1995/1996 parts of South Africa experienced exceptionally high rainf all. Large numbers of Culicoides midges were seen and an outbreak of Africa n horsesickness (AHS) followed. In the Onderstepoort area, near Pretoria in Gauteng, a number of horses died of suspected AHS. Virus isolation and typ ing was done from blood and/or organ samples of 21 suspected cases as well as from five zebra which were kept in the area. Virus was isolated from 14 of the 21 suspected cases but not from the zebra. The neutralizing antibody response of the zebra to the nine different African horsesickness virus (A HSV) serotypes was determined. Results indicated the highest prevalence of serotypes 2 and 4 followed by serotypes 1, 6 and 9. Reverse transcription p olymerase chain reaction (RT-PCR) was performed on total RNA extracted from blood samples of the zebra. AHSV RNA was indicated in three of five zebra by agarose gel electrophoresis analysis of amplicons and in four of five ze bra after Southern blot hybridization using a P-32-labelled probe. RT-PCR c an be used together with serological techniques in studies of AHS to furthe r clarify the epizootiology of the disease.