1. Department of Microbiology, Infectious and Parasitic Diseases, Faculty of Veterinary Medicine, Trakia University, Stara Zagora, Bulgaria.
2. Department of Infectious Diseases, Military Medical Academy, Sofia, Bulgaria.
3. Department of Surgery, Faculty of Veterinary Medicine, University of Forestry, Sofia, Bulgaria.
4. Department of Occupational Medicine, Faculty of Public Health, Medical University, Sofia, Bulgaria.
5. Department de Medicina i Cirurgia Animals, Facultat de Veterinaria, Universitat Autonoma de Barcelona, Barcelona, Spain.