1. Respiratory Diseases of Livestock Research Unit, USDA/Agricultural Research Service/National Animal Disease Center, P.O. Box 70, Ames, Iowa 50010
2. U.S. Public Health Service Commissioned Corps, Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Bacterial and Mycotic Disease, Meningitis and Special Pathogens Branch, Epidemiologic Investigations Laboratory, Atlanta, Georgia 30333