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 Entomology, College of Agriculture and Life Sciences, Iowa State University, Ames, Iowa.
4. Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa.