1. Department of Veterinary Tropical Diseases; Faculty of Veterinary Science; University of Pretoria; Gauteng South Africa
2. Equine Research Centre; University of Pretoria; Gauteng South Africa
3. Department of Medicine and Epidemiology; School of Veterinary Medicine; University of California; USA
4. Department of Pathology; Microbiology and Immunology; School of Veterinary Medicine; University of California; USA