1 Medical University, Faculty of Medicine, Department of Infectious Diseases, Parasitology and Tropical Medicine, Plovdiv, Bulgaria. Electronic address: ivan_balt@yahoo.com.
2 Medical University, Faculty of Medicine, Department of Infectious Diseases, Parasitology and Tropical Medicine, Plovdiv, Bulgaria.
3 Medical University, Faculty of Medicine, Department of Clinical Pathology, Plovdiv, Bulgaria.