1. Hokkaido Research Station; National Institute Animal Health; 4 Hitsujigaoka, Toyohira Sapporo 062-0045 Japan
2. Rumoi Livestock Hygiene Service Center; 11 Miyazono Horonobe 098-3207 Japan
3. Faculty of Agriculture; Miyazaki University; Gakuen kihanadai nishi 1-1 Miyazaki 889-2192 Japan
4. Kyushu Research Station; National Institute of Animal Health; 2702 Chuzan Kagoshima 891-0105 Japan