Department of Veterinary Microbiology and Preventive Medicine, lowa State University, Ames, IA, USA.|Department of Genetics, Development, and Cell Biology, Iowa State University, Ames, IA, USA.|Department of Computer Science, Iowa State University, Ames, IA, USA.|Department of Veterinary Microbiology and Preventive Medicine, lowa State University, Ames, IA, USA.