1. Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
2. Virology Division, United States Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD 21702, USA.
3. Pathology Division, United States Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD 21702, USA.
4. Biosecurity Research Institute and Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506, USA.
5. Center for Aerobiological Sciences, United States Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD 21702, USA.
6. Division of Microbiology, Tulane National Primate Research Center, Covington, LA 70433, USA.
7. Electron Microscopy Laboratory, Cancer Research Technology Program, Frederick National Laboratory for Cancer Research sponsored by the National Cancer Institute, Frederick, MD 21702, USA.