Affiliation: | a Department of Microbiology, University of Iowa College of Medicine, Iowa City, IA 52242, U.S.A. b Department of Physiology, University of Veterinary Science, Budapest, Hungary c National Animal Disease Center, Ames, IA 50010, U.S.A. d Department of Veterinary Science, The Pennsylvania State University, State College, PA 16802, U.S.A. |