MAGDALENA WIECZOREK* and ARLETA KRZYSZTOSZEK National Institute of Public Health – National Institute of Hygiene, Department of Virology, Warsaw, Poland *Corresponding author: M. Wieczorek, National Institute of Public Health – National Institute of Hygiene, Department of Virology, Warsaw, Poland; e-mail: mrechnio@pzh.gov.pl. Submitted 18 December 2015, revised 10 May 2016, ...