1. US Department of Agriculture, National Veterinary Services Laboratories, Animal and Plant Health Inspection Service, 1920 Dayton Avenue, P.O. Box 844, Ames, IA 50010, USA
2. US Department of Agriculture, Southeast Poultry Research Laboratory, US National Poultry Research Center, Agricultural Research Service, 934 College Station Road, Athens, GA 30605, USA
3. Department of Pathobiology and Veterinary Science, University of Connecticut, 61 North Eagleville Road, Unit-3089, Storrs, CT 06269, USA