1. Departamento de Medicina y Cirugia Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, Madrid, Spain.
2. Departamento de Patologia Animal, Medicina Veterinaria, Facultad de Veterinaria, Universidad de León, León, Spain.
3. Department of Veterinary Pathobiology, College of Veterinary Medicine, University of Illinois, Urbana-Champaign, Illinois.