1. 1 Agricultural Research Service, Food Animal Protection Research Laboratory, U.S. Department of Agriculture, 2881 F&B Road, College Station, Texas 77845
2. 2Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, Texas 77843
3. 3Agricultural Research Service, Southeast Poultry Research Laboratory, U.S. Department of Agriculture, 934 College Station Road, Athens, Georgia 30605, USA