1. Virus and Prion Diseases Research Unit, National Animal Disease Center, USDA-ARS, Ames, Iowa.
2. Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa.
3. Faculdade de Agronomia e Medicina Veterinaria, Universidade de Passo Fundo, Bairro Sao Jose, Passo Fundo, Brazil.