1. Department of Microbiology and Immunology, University of Kentucky College of Medicine, MS 415 Chandler Medical Center, Lexington, KY 40536-0298, USA1
2. Microscopy Branch, Rocky Mountain Laboratories, NIAID, National Institutes of Health, 903 South 4th St, Hamilton, MT 59840, USA2
3. Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, PO Box 2087, Foothills Campus, Fort Collins, CO 80522, USA3
4. Department of Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523-1671, USA4