1. Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Ames, Iowa 50011-1250
2. University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103-2714
3. Respiratory Diseases of Livestock Research Unit, USDA Agricultural Research Service, National Animal Disease Center, Ames, Iowa 50010
4. Texas Biotechnology Corporation, Houston, Texas 77030