1. Department of Clinical Veterinary Sciences, University of Liverpool, Leahurst Veterinary Field Station, Chester High Road, Neston, S. Wirral CH64 7TE, United Kingdom
2. Department of Medical Microbiology, University of Liverpool, Duncan Building, Daulby Street, Liverpool L69 3GA, United Kingdom
3. Department of Veterinary Pathology, University of Liverpool, Leahurst Veterinary Field Station, Chester High Road, Neston, S. Wirral CH64 7TE, United Kingdom