1. Department of Rickettsiology, Institute of Epidemiology and Microbiology, Chinese Academy of Preventive Medicine, Beijing, People's Republic of China,
2. Inner Mongolia Anti-Epidemic Station, Huhehot, Inner Mongolia, People's Republic of China,
3. Department of Pathology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27514,
4. and
Hulunbeier District Anti-Epidemic Station, Hailaer, Inner Mongolia, People's Republic of China