1. Saratov Scientific and Research Veterinary Institute of the Federal Agency for Scientific Organizations, Saratov 410028, Russia
2. Scientific Center for Expertise of Medical Application Products, Department of Vaccine Control, Moscow 121002, Russia
3. Consultant, formerly Head, Division of Bacteriology, The National Institute for Biological Standards and Control (NIBSC), Milton Keynes, MK8 8PA, UK
4. Department of Pathology, Department of Microbiology & Immunology, University of Texas Medical Branch, Galveston, TX 77555, USA