1. Immunology and Virology Department, Faculty of Veterinary Medicine, Mahanakorn University of Technology, 140 Cheum-Sampan Rd. Nong Chock, Bangkok 10530, Thailand
2. Clinic for horse, Faculty of Veterinary Medicine, Mahanakorn University of Technology, 140 Cheum-Sampan Rd. Nong Chock, Bangkok 10530, Thailand
3. Laboratory of Animal Health, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan