1. NRL Hepatitis Viruses, Department of Virology, National Center of Infectious and Parasitic Diseases, 1504 Sofia, Bulgaria
2. Department of Epidemiology and Disaster Medicine, Faculty of Public Health, Medical University, 4002 Plovdiv, Bulgaria
3. Department of Social Medicine and Public Health, Faculty of Public Health, Medical University, 4002 Plovdiv, Bulgaria
4. Clinic of Nervous Diseases, University Hospital “Alexandrovska”, Medical University, 1431 Sofia, Bulgaria
5. Department Infectious Diseases, Regional Hospital, 4400 Pazardzhik, Bulgaria
6. NRL Enteroviruses, Department of Virology, National Center of Infectious and Parasitic Diseases, 1504 Sofia, Bulgaria
7. NRL of Vector-Borne Infections, Listeria and Leptospires, Department of Microbiology, National Center of Infectious and Parasitic Diseases, 1504 Sofia, Bulgaria
8. Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, 1000 Sofia, Bulgaria
9. Department of Infectious Diseases, Istituto Superiore di Sanità, 00161 Rome, Italy