Williams, R.; Cohen, A.S.; Grobbelaar, Antoinette A.; Croft, J.E.; Gerdes, Gertruida Hermanna; Wright, Isabel M.; Van Dijk, A.A.; Smith, S.J.
(Published jointly by the Agricultural Research Council, ARC-Onderstepoort Veterinary Institute and the Faculty of Veterinary Science, University of Pretoria., 2003)