ABSTRACT
The history of Wesselsbron (WSL) virus is interwoven with that of Rift Valley fever (RVF) in southern Africa and this has had a marked influence on the manner in which WSL virus is perceived. WSL virus was found to be pathogenic for newborn lambs and pregnant ewes, but produced mild infection in nonpregnant cattle, horses, and pigs. The use of RVF vaccine appeared to control sheep abortions and neonatal mortality on some farms, but not on others. WSL virus was subsequently isolated from the organs of a cow which died during a RVF epizootic in Zimbabwe in 1978. Establishing an etiological diagnosis in an outbreak of teratology in livestock can be an intractable problem. Diagnostic procedures should be optimized through use of sensitive methods for demonstrating virus or antigen in animal tissues, and for detecting and demonstrating the specificity of antibodies to flaviviruses in fetal and adult sera.
