1. Animal Diseases Research Institute, PO Box 11300, Station H, Nepean, ON K2H 8P9, Canada
2. Institute for Animal Health, Pirbright Laboratory, Ash Road, Pirbright, Surrey GU24 0NF, UK
3. National Veterinary Services Laboratories, USDA, APHIS, PO Box 844, Ames, IA 50010