1. Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada
2. Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada
3. Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
4. Department of Veterinary Medicine, University of Cambridge, Cambridge, UK
5. Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada