1. Shikoku Veterinary Medical Center, Kagawa, Japan
2. Shikoku Cytopathological Laboratory, Kagawa, Japan
3. Enteric Pathogen Group, Division of Zoonosis Research, National Institute of Animal Health, National Agriculture and Food Research Organization, Ibaraki, Japan
4. Laboratory of Veterinary Pathology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan