1. a Animal Health Laboratory , University of Guelph , Box 3612, Guelph , Ontario , Canada , N1H 6R8
2. b Faculté de Médecine Vétérinaire , Université de Montréal , CP 5000, 3200 rue Sicotte, Saint-Hyacinthe , Québec , Canada , J2S 7C6
3. c Department of Veterinary Pathology, Western College of Veterinary Medicine , University of Saskatchewan , Saskatoon , Saskatchewan , Canada , S7N 5B4