1. College of Medicine and Medical Research Institute, Chungbuk National University, 12 Gaeshin-Dong Heungduk-Ku, Cheongju 361-763, Republic of Korea
2. College of Veterinary Medicine, Chungnam National University, 220 Gung-Dong, Yuseoung-Gu, DaeJeon 305-764, Republic of Korea
3. Division of Bioscience and Technology, College of Life and Environmental Science, Korea University, Seoul, Republic of Korea
4. Division of Virology, Department of Infectious Diseases, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, Tennessee 38105