1. Research Unit, Green Cross Veterinary Products, Yong-In, 449-903, Korea
2. Research Unit, Anigen, Suwon, 440-290 Korea
3. Department of Veterinary Medicine Virology Laboratory, College of Veterinary Medicine and School of Agricultural Biotechnology, Seoul National University, Gwanak-gu, Seoul, 151-742, Korea
4. Division of Biological Science and the Institute for Molecular Biology and Genetics, Chonbuk National University, Jeonju, 561-756, Korea