1. Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary MedicineIowa State University 50010 Ames IA USA
2. Department of Veterinary Clinical Medicine and the Veterinary Diagnostic Laboratory, College of Veterinary MedicineUniversity of Illinois 61802 Urbana IL USA
3. National Animal Disease CenterUSDA-ARS 50010 Ames IA USA
4. State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research InstituteChinese Academy of Agricultural Sciences
678 Haping Street
150069 Harbin China