1 Department of Microbiology, Immunology, and Pathology, Colorado State University, Campus Delivery 1690, Fort Collins, CO 80523, USA.
2 Division of Vector-borne Diseases, Arboviral Diseases Branch, Centers for Disease Control and Prevention, Fort Collins, CO 80521, USA.
3 Departments of Medicine, Neurology, and Immunology & Microbiology, Division of Infectious Diseases, University of Colorado School of Medicine, Rocky Mountain Regional VAMC, 12,700 E. 19th Avenue, B168, Denver, CO 80045, USA.