Rapid detection of Bombyx mori nucleopolyhedrovirus (BmNPV) by loop-mediated isothermal amplification assay combined with a lateral flow dipstick method

Fast identification of the BmNPV infected silkworms by portable NIR spectroscopy and chemometrics

A convenient, low-cost, and rapid detection of BmNPV-infected silkworms is of great significance for the safety of the sericulture industry. In this study, a portable NIR system was used to collect the spectra of normal silkworms and the infected silkworms induced by the administration of Bombyx mori nuclear polyhedrosis virus (BmNPV). Different spectral pretreatment methods were applied, then principal component analysis (PCA), linear discriminant analysis (LDA), and partial least squares discriminant analysis (PLSDA) were used for the classification analysis. The results showed that PCA and LDA were unable to achieve the purpose. For the PLSDA calibration, after the pretreatment of SNV combining 2nd derivative, it had a high identification performance, and obtained low classification errors of 0.023, 0.033, and 0.030 for the calibration set, cross-validation set, and test set, respectively, with higher sensitivity and specificity. Therefore, the BmNPV-infected silkworms can be identified by portable NIR spectroscopy, which will effectively reduce losses for the sericulture industry.

An electrochemical immunosensor based on hybrid self-assembled monolayers for rapid detection of Bombyx mori nucleopolyhedrovirus

Bombyx mori nucleopolyhedrovirus (BmNPV) is highly contagious and poses a serious threat to sericulture production. Because there are currently no effective treatments for BmNPV, a rapid and simple detection method is urgently needed. This paper describes an electrochemical immunosensor for the detection of BmNPV. The immunosensor was fabricated by covalently immobilizing anti-BmNPV, a biorecognition element, onto the surface of the working gold electrode via 11-mercaptoundecanoic acid (MUA)/β-mercaptoethanol (ME) hybrid self-assembled monolayers. Electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) were used to characterize the electrochemical performance and morphology of the immunosensor, respectively. Under optimum conditions, the developed immunosensor exhibited a linear response to BmNPV polyhedrin in the range of 1 × 102-1 × 108 fg/mL, with a low detection limit of 14.54 fg/mL. The immunosensor also exhibited remarkable repeatability, reproducibility, specificity, accuracy, and regeneration. Normal silkworm blood was mixed with BmNPV polyhedrin and analyzed quantitatively using this sensor, and the recovery was 92.31 %-100.61 %. Additionally, the sensor was used to analyze silkworm blood samples at different time points after BmNPV infection, and an obvious antigen signal was detected at 12 h post infection. Although this result agreed with that provided by the conventional polymerase chain reaction (PCR) method, the electroanalysis method established in this study was simpler, shorter in detection period, and lower in material cost. Furthermore, this innovative electrochemical immunosensor, developed for the ultra-sensitive and rapid detection of BmNPV, can be used for the early detection of virus-infected silkworms.

Recombinase-aided amplification coupled with lateral flow dipstick for efficient and accurate detection of Bombyx mori nucleopolyhedrovirus

The infection of Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the main causes of economic losses in sericulture. Thus, it is essential to establish rapid and effective method for BmNPV detection. In the present study, we have developed a recombinase-aided amplification (RAA) to amplify the BmNPV genomic DNA at 37 °C within 30 min, and achieved a rapid detection method by coupling with a lateral flow dipstick (LFD). The RAA-LFD method had a satisfactory detection limit of 6 copies/μL of recombinant plasmid pMD19-T-IE1, and BmNPV infection of silkworm can be detected 12 h post-infection. This method was highly specific for BmNPV, and without cross-reactivity to other silkworm pathogens. In contrast to conventional polymerase chain reaction (PCR), the RAA-LFD assay showed higher sensitivity, cost-saving, and especially is apt to on-site detection of BmNPV infection in the sericulture production.

Recent advances in the biosensors application for reviving infectious disease management in silkworm model: a new way to combat microbial pathogens

Silkworms are an essential economic insect but are susceptible to diseases during rearing, leading to yearly losses in cocoon production. While chemical control is currently the primary method to reduce disease incidences, its frequent use can result in loss of susceptibility to pathogens and, ultimately, antibiotic resistance. To effectively prevent or control disease, growers must accurately, sensitively, and quickly detect causal pathogens to determine the best management strategies. Accurate recognition of diseased silkworms can prevent pathogen transmission and reduce cocoon loss. Different pathogen detection methods have been developed to achieve this objective, but they need more precision, specificity, consistency, and promptness and are generally unsuitable for in-situ analysis. Therefore, detecting silkworm diseases under rearing conditions is still an unsolved problem. As a consequence of this, there is an enormous interest in the development of biosensing systems for the early and precise identification of pathogens. There is also significant room for improvement in translating novel biosensor techniques to identify silkworm pathogens. This study explores the types of silkworm diseases, their symptoms, and their causal microorganisms. Moreover, we compare the traditional approaches used in silkworm disease diagnostics along with the latest sensing technologies, with a precise emphasis on lateral flow assay-based biosensors that can detect and manage silkworm pathogens.

Development of a rapid visual detection technology for BmNPV based on CRISPR/Cas13a system

Pathogenic microorganism of silkworm are important factors that threaten the high-quality development of sericulture. Among them, Bombyx mori nucleopolyhedrovirus (BmNPV) caused diseases often lead to frequent outbreaks and high mortality, resulting in huge losses to sericultural industry. Current molecular detection methods for BmNPV require expensive equipment and sikilled technical personnel. As a result, the most commonly detection method for silkworm egg production enterprises involves observing the presence of polyhedra under a microscope. However, this method has low accuracy and sensitivity. There is an urgent need to develop a new detection technology with high sensitivity, high specificity, and applicability for silkworm farms, silkworm egg production enterprises and quarantine departments. In this study, we successfully established the CRISPR/Cas13a BmNPV visualized detection technology by combining Recombinase Polymerase Amplification (RPA) technology and CRISPR/Cas13a system. This technology is based on microplate lateral, flow test strips and portable fluorescence detector. The detection sensitivity can reach up to 1 copies/μL for positive standard plasmid and 1 fg/μL for BmNPV genome in 30-45 min, demonstrating high sensitivity. By detecting silkworm tissues infected with different pathogens, we determined that CRISPR/Cas13a detection technology has good specificity. In summary, the newly established nucleic acid detection technology for BmNPV is characterized by high sensitivity, high specificity, low cost and convenience for visualization. It can be applied in field detection and silkworm egg quality monitory system.

Rapid and effective detection of Macrobrachium rosenbergii nodavirus using a combination of nucleic acid sequence-based amplification test and immunochromatographic strip

Nucleic acid sequence-based amplification (NASBA) provides a fast and convenient approach for nucleic acid amplification under isothermal conditions, and its combination with an immunoassay-based lateral flow dipstick (LFD) could produce a higher detection efficiency for M. rosenbergii nodavirus isolated from China (MrNV-chin). In this study, two specific primers and a labelled probe of the capsid protein gene of MrNV-chin were constructed. The process of this assay mainly included a single-step amplification at a temperature of 41 ℃ for 90 min, and hybridization with an FITC-labeled probe for 5 min, with the hybridization been required for visual identification during LFD assay. The test results indicated that, the NASBA-LFD assay showed sensitivity for 1.0 fg M. rosenbergii total RNA with MrNV-chin infection, which was 10⁴ times that of the present RT-PCR approach for the detection of MrNV. In addition, no products were created for shrimps with infection of other kinds of either DNA or RNA virus, which indicated that the NASBA-LFD was specific for MrNV. Therefore, the combination of NASBA and LFD is a new alternative detection method for MrNV which is rapid, accurate, sensitive and specific without expensive equipment and specialised personnel. Early detection of this infectious disease among aquatic organisms will help implement efficient therapeutic strategy to prevent its spread, enhance animal health and limit loss of aquatic breeds in the event of an outbreak.

Detection of cyprinid herpesvirus 2 by loop-mediated isothermal amplification in combination with a lateral flow dipstick

We developed a convenient technique to detect Herpesviral haematopoietic necrosis attributed to cyprinid herpes virus 2 (CyHV-2), a serious disease of Crucian carp and goldfish related to high mortality. In the present study, we employed a lateral flow dipstick (LAMP-LFD) to present a loop-mediated isothermal amplification assay. The specificity was ascertained via other six viruses, and the sensitivity was compared using PCR method, which are the reaction conditions changes for the method improved. The results revealed that CyHV-2 performance was observable at 64 °C in a separated tube within 60 min, when the samples hybridized using an FITC-labeled probe. As the LAMP-LFD method's specificity was high, with its sensitivity identical to that of traditional PCR, the overall DNA collected revealed the lowest detection limit of 0.18 pg/μl from goldfish diseased by CyHV-2. In summary, the development of LAMP-LFD's method does not require expensive instruments, and it can be regarded as a fast, simple, and reliable method for CyHV-2 detection.

Rapid detection of Bombyx mori bidensovirus by loop-mediated isothermal amplification based lateral flow dipstick assay for field applications

Bombyx mori bidensovirus (BmBDV), is the only bipartite single-stranded DNA (ssDNA) insect virus reported to date. BmBDV causes fatal flacherie disease in silkworm, resulting in large economic losses to sericulture. We developed a loop-mediated isothermal amplification with lateral flow dipstick (LAMP-LFD) method that can successfully and rapidly detect BmBDV DNA with a low limit of detection (5 fg, 400 copies of the BmBDV genome). The method was evaluated and improved for direct field diagnosis using silkworm faeces. In the field, the actual limit of detection was ∼50 fg (4000 copies of the BmBDV genome). The results demonstrated that, compared with traditional methods for BmBDV detection, our new LAMP-LFD method was much more rapid, sensitive and cost-effective, with less dependence on equipment, making it easier to use. The method has potential to be translated into a new diagnostic product for field applications in the sericulture industry.

The development and application of a duplex reverse transcription loop-mediated isothermal amplification assay combined with a lateral flow dipstick method for Macrobrachium rosenbergii nodavirus and extra small virus isolated in China

White tail disease (WTD), a major disease prevailing in the larval stage of Macrobrachium rosenbergii, caused by Macrobrachium rosenbergii nodavirus (MrNV) associated with extra small virus (XSV), led to the economic loss of shrimp industry in China. In order to establish a convenient, sensitive and selective molecular diagnostic method to detect MrNV and XSV for the Chinese shrimp (MrNV/XSV-chin), a reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay combined with a lateral flow dipstick (LFD) method were developed. A set of four specific primers and a labeled probe were designed according to the six conserved gene sequence regions encoding for the MrNV capsid protein CP43 and the XSV capsid protein CP17. The detection of MrNV and XSV simultaneously by RT-LAMP was performed at 61 °C in a single reaction for 60 min followed by hybridization with an FITC-labeled probe for 5 min and visualized by LFD. The RT-LAMP-LFD assay had a sensitivity of approximately 100-fold higher than conventional PCR. In addition, the assay could detect MrNV/XSV-chin from limited amount of RNA extracts as low as 1.0 pg extracted from Macrobrachium rosenbergii. This assay was simple to use, required little instrumentation, and exhibited excellent specificity for the MrNV/XSV-chin compared with other shrimp viruses. In conclusion, a convenient, sensitive and selective practical molecular diagnostic method was developed with the potential for diagnosis and prevention of WTD.