1. Hokubu Agricultural Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Hyogo 669-5254, Japan
2. Department of Advanced Pathobiology, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Osaka 598-8531, Japan
3. Asago Animal Hygiene Institute of Hyogo Prefecture, Hyogo 669-5243, Japan