1. Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa.
2. Department of Entomology, College of Agriculture, Iowa State University, Ames, Iowa.
3. Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa.
4. Animal Resources, College of Veterinary Medicine, Iowa State University, Ames, Iowa.
5. Department of Pathology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.