1. Department of Pathology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.
2. Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa.
3. Department of Veterinary Diagnostic and Production Animal Medicine, and the Department of Statistics and Statistical Laboratory, College of Veterinary Medicine, and College of Liberal Arts and Sciences, Iowa State University, Ames, Iowa.
4. Department of Entomology, College of Agriculture, Iowa State University, Ames, Iowa.