2.1. Virus preparation
The HPAI A/duck/HongKong/1091/2011 (H5N1) belonging to
clade 2.3.2 was used in this study. A stock of the virus was
propagated by one passage in Mardin-Darby canine kidney (MDCK)
cells which yielded a final titer of 1 107.5 median tissue culture
infectious dose (TCID50)/ml. On the day of inoculation the virus
stock was diluted to a concentration of 3.3 103 TCID50/ml with
phosphate-buffered saline (PBS)