1. Department of Physiology and Pathophysiology, Faculty of Medicine, Medical University of Varna, Varna, Bulgaria;
2. Department of General and Clinical Pathology, Forensic Science and Deontology, Faculty of Medicine, Medical University of Varna, Varna, Bulgaria;
3. Second Department of Internal Medicine, Faculty of Medicine, Medical University of Varna, Varna, Bulgaria;
4. Gastroenterology Unit, University Hospital “Aleksandrovska”, Sofia, Bulgaria;
5. Department of Anatomy and Histology, College of Medicine “Yordanka Filaretova”, Sofia, Bulgaria;
6. Hematology Department, Military Medical Academy, Sofia, Bulgaria;
7. Department of Virology, The Stephan Angeloff Institute of Microbiology, Bulgarian Academy of Sciences, Sofia, Bulgaria