African Swine Fever (ASF), caused by African swine fever virus (ASFV), is a highly contagious and lethal viral disease of pigs. However, commercial vaccines are not yet available, and neither are drugs to prevent or control ASF. Therefore, rapid, accurate on-site diagnosis is urgently needed for detection during the early stages of ASFV infection. Herein, a cleaved probe-based loop-mediated isothermal amplification (CP-LAMP) detection method was established. Based on the original primer sets, we targeted the ASFV 9GL gene sequence to design a probe harboring a ribonucleotide insertion. Ribonuclease H2 (RNase H2) enzyme activity can only be activated when the probe is perfectly complementary, resulting in hydrolytic release of a quencher moiety, and consequent signal amplification. The method displayed robust sensitivity, with copy number detection as low as 13 copies/µL within 40 min at constant temperature (62°C). Visualization of the fluorescence product was employed using a self-designed 3D-printed visualization function cassette, and the CP-LAMP method achieved specific identification and visual detection of ASFV. Moreover, coupling the dual function cassette and smartphone quantitation makes the CP-LAMP assay first user-friendly, cost-effective, portable, rapid, and accurate point-of-care testing (POCT) platform for ASFV.
Porcine deltacoronavirus (PDCoV) causes watery diarrhea, vomiting, and 30–40% mortality in newborn piglets. A simple, rapid, and sensitive method for PDCoV detection is valuable in its surveillance and control. Here, we developed a novel, cleaved probe-based reverse transcription loop-mediated isothermal amplification (CP-RT-LAMP) method for PDCoV detection. A cleaved probe with a ribonucleotide insertion that targeted the N gene of PDCoV was designed. During the reaction, the enzyme ribonuclease H2 is activated only when the cleaved probe is perfectly complementary to the template, leading to the hydrolytic release of a quencher moiety and signal output. This method can be easily used on a real-time fluorescence quantitative equipment or an on-site isothermal instrument combined with a smartphone. The specificity assay showed no cross-reactivity with other porcine enteric pathogens. This method had a detection limit of 25 copies/μL, suggesting comparable sensitivity with reverse transcription quantitative PCR (RT-qPCR). In detecting 100 clinical samples (48 fecal swab specimens and 52 intestinal specimens), the detection rate of the CP-RT-LAMP method (26%) was higher than that of RT-qPCR (17%). Thus, it is a highly specific and sensitive diagnostic method for PDCoV, with a great application potential for monitoring PDCoV in the laboratory or point-of-care testing in the field.
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