1. Department of Microbiology, Faculty of Public Health; Mahidol University, Rajvithi Road; Bangkok 10400 Thailand
2. Department of Parasitology, Faculty of Public Health; Mahidol University, Rajvithi Road; Bangkok 10400 Thailand
3. Department of Global Epidemiology, Research Center for Zoonosis Control; Hokkaido University; Sapporo Hokkaido 001-0021 Japan