1. United States Department of Agriculture, Animal Plant Health Inspection Service, Veterinary Services, 5825 Florida Blvd., Suite 1140, Baton Rouge, Louisiana 70806, USA
2. Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas 77843-4467, USA
3. Department of Veterinary Physiology & Pharmacology, Texas A&M University, College Station, Texas 77843-4466, USA
4. United States Department of Agriculture, Animal Plant Health Inspection Service, Veterinary Services, 4700 River Road, Unit 36, 3A-34, Riverdale, Maryland 20737-5573, USA