1. Department of Virology National Center of Infectious and Parasitic Diseases Sofia Bulgaria
2. The National Specialized Hospital for Active Treatment in Haematological Diseases Sofia Bulgaria
3. University Hospital “St Ivan Rilski,” Sofia Bulgaria
4. Oncology Institute of Vojvodina Sremska Kamenica Serbia
5. Faculty of Medicine University of Novi Sad Novi Sad Serbia
6. Institute of Microbiology and Virology Riga Stradins University Riga Latvia