Abstract
Division of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia1
Department of Veterinary Science, The Queens University of Belfast, Stormont, Belfast BT4 3SD, Northern Ireland2
Electron Microscopy Laboratory, Istituto Zooprofilattico Sperimentale della Lombardia e dellEmilia Romagna, Via Bianchi 9, 25124 Brescia, Italy3
Department of Agriculture and Rural Development for Northern Ireland, Stormont, Belfast BT4 3SD, Northern Ireland4