1. Ibaraki Prefecture Livestock Research Center, Ibaraki 315-0132, Japan
2. Ibaraki Prefecture Livestock Hygiene Service Center, Ibaraki 310-0002, Japan
3. PRIME TECH LTD, Ibaraki 300-0841, Japan
4. Tokyo University of Agriculture, Kanagawa 243-0034, Japan
5. Center for Animal Disease Control and Prevention, National Institute of Animal Health, Ibaraki 305-0856, Japan
6. Present: Zen-noh Institute of Animal Health, Chiba 285-0043, Japan
7. Division of Animal Sciences, National Institute of Agrobiological Sciences, Ibaraki 305-0901, Japan