1. Special Pathogens Program, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba R3E 3R2, Canada.
2. Department of Medical Microbiology, University of Manitoba, Winnipeg, Manitoba R3E 0J9, Canada.
3. Department of Immunology, University of Manitoba, Winnipeg, Manitoba R3E 0T5, Canada.
4. Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.