Comparison of sensitivity of 4 methods in NDV detection. (A) Sensitivity test of PCR. 1–8: 107–100 copies/μL, respectively; 9: Negative control. The results showed the minimum template concentration for the occurrence of the obvious single band was 103 copies/μL, which was the LDL for PCR. (B) Sensitivity test of RT-RAA-LFD. 1–7: 106–100 copies/μL, respectively; 8: Negative control. The results showed the minimum template concentration for the occurrence of the obvious test line was 102 copies/μL, which was the LDL for RT-RAA-LFD. (C) Sensitivity test of RFQ-PCR. 1: Negative control; 2–8: 100–106 copies/μL. The results showed the minimum template concentration for the occurrence of obvious amplification curve was 10 copies/μL, which was the LDL for RFQ-PCR. (D) Sensitivity test of RF-RT-RAA. 1: Negative control; 2–6: 100–104 copies/μL, respectively. The results showed the minimum template concentration for the occurrence of obvious amplification curve was 10 copies/μL, which was the LDL for RF-RT-RAA. Abbreviations: LDL, lowest detectable limit; NDV, Newcastle disease virus; RT-RAA-LFD, reverse transcription recombinase–aided amplification-lateral flow dipstick; RF-RT-RAA, real-time fluorescence-based reverse transcription recombinase–aided amplification; RFQ-PCR, real-time fluorescence–based quantitative PCR.