1. Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, MT, USA
2. Animal and Plant Health Agency (APHA), Lasswade Laboratory, Bush Loan, Penicuik, Midlothian, Scotland, UK
3. Electron Microscopy Section, Research Technology Branch, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, MT, USA