1. Department of Veterinary Public Health, Faculty of Agriculture, Tottori University, Tottori 680-0945, Japan
2. Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Drive West, Madison, Wisconsin 53706, U.S.A.
3. Laboratory Animal Research Center, Institute of Medical Science, The University of Tokyo, Tokyo 108-0071, Japan
4. Laboratory of Microbiology, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan