For viral NA amplification (both DNA and RNA virus) we used the described WTA method [2] by using the QuantiTect Whole Transcriptome Amplification kit (typical yield ,40 mg from a 50 ml reaction, Qiagen) according to manufacturer's protocol, except for the reverse transcription step that was replaced by the Superscript VILO kit (Invitrogen) described above. The WTA protocol includes 3 sequential reactions: first a reverse transcription reaction to generate cDNA, secondly a ligation of generated cDNA into larger transcriptomes and thirdly a Phi29-amplification of the generated transcriptomes. Briefly, as described above, 14 ml of extracted viral NA was put into a 20 ml-VILO reaction and incubated at 42uC for 1 hour. The Superscript enzyme was inactivated at 95uC for 5 minutes, 10 ml of the VILO cDNA reaction was added to 10 ml of ligation mix and incubated at 22uC for 2 hours. Thirty microliters of amplification mix containing Phi29 polymerase and random primers was then added and amplification performed at 30uC for 8 hours. The reaction was terminated by incubation at 95uC for 5 minutes. Amplified material was purified using QIAamp DNA mini kit (Qiagen) using a modified protocol (www.qiagen.com), and checked for purity and concentration using a NanoDrop spectrophotometer (Thermo Scientific) and agarose gel electrophoresis. The DNA was stored at 280uC or immediately used for microarray analysis.