1. Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, CO 80521, USA.
2. Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523, USA.
3. Division of Infectious Diseases,Department of Medicine, New York Medical College, Valhalla, NY 10595, USA.
4. Department of Statistics, Colorado State University, Fort Collins, CO 80523, USA.
5. Division of Immunology and Pathogenesis, Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL 32816, USA.