1. Department of Veterinary Pathology, Faculty of Veterinary Medicine, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil
2. Louisiana Animal Disease Diagnostic Laboratory, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA
3. Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA
4. Current address: Department of Comparative Pathobiology, Indiana Animal Disease Diagnostic Laboratory, College of Veterinary Medicine, Purdue University, West Lafayette, IN, USA
5. current address: Department of Veterinary Medicine and Surgery, Division of Basic Sciences, MD Anderson Cancer Center, The University of Texas, Houston, TX, USA