1. Departement de Pathologie et Microbiologic, Faculté de Médecine Vétérinaire, Université de Montréal, C.P. 5000, St.-Hyacinthe, Quebec J2S 7C6, Canada
2. Laboratoire de Pathologie Animale, MAPAQ, 2700 Einstein, Ste.-Foy, Quebec G1P 3W8, Canada
3. Department of Veterinary PathoBiology, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108