1 WHO Collaborating Centre for Reference and Research on Tropical and Emerging Virus Diseases, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan.
2 National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
3 Institute of Hygiene and Epidemiology of Tay Nguyen, Dak Lak, Vietnam.
4 Preventive Medicine Center, Krong Buk District, Vietnam.
5 WHO Collaborating Centre for Reference and Research on Tropical and Emerging Virus Diseases, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan. Electronic address: rainbow@nagasaki-u.ac.jp.