Visual detection of turkey coronavirus RNA in tissues and feces by reverse-transcription loop-mediated isothermal amplification (RT-LAMP) with hydroxynaphthol blue dye

A sensitive reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for the rapid visual detection of turkey coronavirus (TCoV) infection. The reaction is performed in one step in a single tube at 65 °C for 45 min, with hydroxynaphthol blue (HNB) dye added prior to amplification. The detection limit of the RT-LAMP assay was approximately 10(2) EID(50/50 μl) TCoV genome, and no cross-reaction with other avian viruses was observed. The assay was evaluated further in tissue suspensions prepared from the ileum and ileum–caecal junctions of infected turkey embryos; 100% of these samples were positive in the RT-LAMP assay. All individual feces samples collected in the field were considered positive by both conventional RT-PCR and RT-LAMP. In conclusion, RT-LAMP with HNB dye was shown to be a sensitive, simple assay for the rapid diagnosis of TCoV infection, either directly from feces or in association with virus isolation methods.