Extraction and Analysis of Viral DNA/RNA

CaHV DNA was extracted from the crucian carp infected with CaHV, by using skin mucus swabbing and the disc method as we described before (Gui et al., 2022 (link)). Briefly, healthy crucian carp were injected intraperitoneally with diseased fish tissue filtrate (viral suspension) kindly provided by Dr. Qiya Zhang (Institute of Hydrobiology, Chinese Academy of Sciences). Other viruses, including CyHV-2 (NC_019495), KHV (NC_009127), IHNV (NC_001652), SVCV (NC_002803), and GCRV-JX01 (MG189638.1), were previously stored in the laboratory. DNA of CyHV-2 and KHV were extracted with a Viral RNA/DNA Extraction Kit (Code No. 9766, Takara Biotechnology Co., Ltd., China), which was carried out in accordance with the instructions of the kit. RNA of GCRV-JX01, IHNV and SVCV were extracted with TRIzol reagent (Invitrogen, USA), which was performed in accordance with the manufacturer’s instructions. Complementary DNA (cDNA) was reverse transcribed by using PrimeScript reverse transcription system (Code No. 2680A, Takara Biotechnology Co., Ltd., China) in accordance with the product protocol, as described in previous study (Wang et al., 2018 (link); Feng et al., 2022 (link)). All samples were stored at − 80°C until use.