1. Department of Clinical Studies - Philadelphia; School of Veterinary Medicine; University of Pennsylvania; 3900 Delancey St Philadelphia PA 19104 USA
2. Department of Clinical Sciences and Services; Royal Veterinary College; University of London; Hawkshead Lane North Mymms Hertfordshire AL9 7TA UK
3. Department of Environmental Health and Engineering; Johns Hopkins Bloomberg School of Public Health; 615 N. Wolfe St Baltimore MD 21205 USA
4. Department of Biomedical Sciences; School of Veterinary Medicine; Ross University; Basseterre St Kitts and Nevis, West Indies
5. Department of Pathobiology; Ontario Veterinary College; University of Guelph; Guelph ON Canada N1G 2W1