1 Department of Infectious Diseases, Parasitology and Dermatovenerеology, Faculty of Medicine, Medical University "Prof. Dr. Paraskev Stoyanov" - Varna, Bulgaria.
2 Specialized Medical Diagnostic Laboratory "Status", Varna, Bulgaria.
3 Department of Anatomy, Histology and Embryology, Faculty of Medicine, Medical University "Prof. Dr. Paraskev Stoyanov" - Varna, Bulgaria.
4 Department of Hygiene and Epidemiology, Faculty of Public Health, Medical University "Prof. Dr. Paraskev Stoyanov" - Varna, Bulgaria.