1. Department of Clinical Microbiology, Royal Victoria Infirmary, Newcastle upon Tyne NE1 4LP,1
2. Departments of Microbiology & Immunology2 and
3. Physiological Sciences,3 The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, and
4. Zoonotic and Animal Pathogens Research Laboratory, Department of Veterinary Pathology, University of Edinburgh, Edinburgh EH8 9AG,4 United Kingdom