1. Universitaet Hannover, Welfengarten 1, 30169 Hannover, Germany.
2. PCVET, Escuela de Medicina Veterinaria, Universidad Nacional Apdo 304–3000 Heredia, Costa Rica.
3. Center of Veterinary Epidemiology and Animal Disease Surveillance Systems, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523–1676.