1. Division of Infectious Diseases, Department of Medicine, Faculty of Medicine, University of British Columbia, 2733 Heather Street, Vancouver, British Columbia V5Z 3J5, Canada, Centre for Microbial Diseases and Immunity Research, University of British Columbia, 2259 Lower Mall, Vancouver, British Columbia V6T 1Z4, Canada, and Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia V6T 1Z4, Canada