Reverse transcription recombinase polymerase amplification with lateral flow dipsticks for detection of influenza A virus and subtyping of H1 and H3

Graphene-Based Virus Enrichment Protocol Increases the Detection Sensitivity of Human Norovirus in Strawberry and Oyster Samples

Human noroviruses (HuNoVs), the most prevalent viral contaminant in food, account for a substantial proportion of nonbacterial gastroenteritis cases. Extensive work has been focused on the diagnosis of HuNoVs in clinical samples, whereas the availability of sensitive detection methods for their detection in food is lacking. Here, we developed a virus enrichment approach utilizing graphene-based nanocomposites (CTAB-rGO-Fe3O4) that does not rely on large instruments and is suitable for on-site food pretreatment. The recovery efficiency of the developed virus enrichment procedure for serially diluted GII.4 norovirus ranged from 10.06 to 72.67% in strawberries and from 2.66 to 79.65% in oysters. Furthermore, we developed a real-time recombinase polymerase amplification (real-time RPA) assay, which can detect as low as 1.22 genome copies µL-1 of recombinant plasmid standard and has no cross-reactivity with genomes of astrovirus, rotavirus, adenovirus, and MS2 bacteriophage. Notably, the combined virus enrichment and real-time RPA detection assay enhanced the detection limits to 2.84 and 37.5 genome copies g-1 in strawberries and oysters, respectively, compared to those of qPCR. Our strategy, the graphene-based virus enrichment method combined with real-time RPA, presents a promising tool for sensitively detecting HuNoVs in food samples.

Current status of diagnostic assays for emerging zoonotic viruses: Nipah and Hendra

INTRODUCTION

Nipah and Hendra viruses belong to the Paramyxoviridae family, which pose a significant threat to human health, with sporadic outbreaks causing severe morbidity and mortality. Early symptoms include fever, cough, sore throat, and headache, which offer little in terms of differential diagnosis. There are no specific therapeutics and vaccines for these viruses.

AREAS COVERED

This review comprehensively covers a spectrum of diagnostic techniques for Nipah and Hendra virus infections, discussed in conjunction with appropriate type of samples during the progression of infection. Serological assays, reverse transcriptase Real-Time PCR assays, and isothermal amplification assays are discussed in detail, along with a listing of few commercially available detection kits. Patents protecting inventions in Nipah and Hendra virus detection are also covered.

EXPERT OPINION

Despite several outbreaks of Nipah and Hendra infections in the past decade, in-depth research into their pathogenesis, Point-of-Care diagnostics, specific therapies, and human vaccines is lacking. A prompt and accurate diagnosis is pivotal for efficient outbreak management, patient treatment, and the adoption of preventative measures. The emergence of rapid point-of-care tests holds promise in enhancing diagnostic capabilities in real-world settings. The patent landscape emphasizes the importance of innovation and collaboration within the legal and business realms.

Rapid and Visual Detection of Actinidia Chlorotic Ringspot-Associated Virus Using One-Step Reverse-Transcription Recombinase Polymerase Amplification Combined with Lateral Flow Dipstick Assay

Actinidia chlorotic ringspot-associated virus (AcCRaV) occurs widely in major kiwifruit producing areas of China and is often accompanied by coinfecting viruses, affecting the growth, yield, and quality of kiwifruit. Therefore, a rapid and sensitive detection method is crucial for diagnosing and developing effective AcCRaV management strategies. In this study, a one-step reverse-transcription recombinase polymerase amplification combined with a lateral flow dipstick (RT-RPA-LFD) assay was developed for rapid detection of AcCRaV. Specific primers and a probe were designed based on the conserved region of the coat protein gene sequence of AcCRaV. The one-step RT-RPA reaction can be performed at 35 and 40°C within 10 to 30 min, and the amplification results can be read directly on the LFD within 5 min. The detection limit of the one-step RT-RPA-LFD assay was 10-8 ng (about 20 viral copies), which was equal with one-step RT-qPCR and 100 times more sensitive than one-step RT-PCR. Moreover, the one-step RT-RPA-LFD assay was successfully applied to detect AcCRaV from crude extracts, and the entire detection process can be completed within 40 min. These results indicate that the RT-RPA-LFD assay is a simple, rapid, and sensitive strategy that can be used for accurate diagnosis of AcCRaV-infected kiwifruit plants in the field. To our knowledge, this is the first study applying the one-step RT-RPA-LFD assay to detect a kiwifruit virus.

A recombinase polymerase amplification (RPA) combined with strip visualization method for RNA-based presumptive tests of saliva and vaginal secretion

Identifying the origin of body fluids is a critical step in a forensic investigation. One widely used method to identify human body fluids is based on the color visualization of immune antigen detection strips for detecting hemoglobin in blood and prostate-specific antigen in semen. It is highly imperative to construct an easy-to-perform, mRNA-based method for the point-of-care identification of other human body fluids, such as saliva and vaginal secretion. Here, we established specific strips with the mRNA markers STATH (for saliva) and SPINK5 (for vaginal secretion) via reverse transcription recombinase polymerase amplification (RT-RPA) and lateral flow dipstick (LFD) assays (RT-RPA-LFD). RT-RPA could be accomplished in a single tube at a wide temperature range of 30-42 ℃ within 10-25 min if we do not count time for RNA extraction. The diluted RPA products were added onto the LFD strip pad to visually observe the color change of the Control/Test line. The tissue specificity and detection limit of the assays were evaluated using the optimized reaction conditions of RPA at 37 ℃ for 15 min. The positive signals of STATH were observed both in saliva and nasal secretions. SPINK5 was positive in a template-dependent manner in 4 out of 30 female urine samples in addition to vaginal secretion and menstrual blood samples. Cross-reactions were not detected in semen, skin swabs, sweat, or male urine. Both assays were capable of detecting aged samples, which were stored for 180 days (saliva) or 300 days (vaginal secretion) at room temperature. Moreover, saliva or vaginal secretion was successfully detected in all kinds of mixtures made from various body fluids. Overall, the rapid strip test method by the RT-RPA-LFD assay is simple, time-saving and highly sensitive for estimating the tissue origin of saliva and vaginal secretion. This method for the rapid RNA-based presumptive tests of the tissue type of body fluids is easy to perform prior to a multiplex mRNA analysis, which can demonstrate more reliable saliva or vaginal secretion identification.

Critical insight into recombinase polymerase amplification technology

INTRODUCTION

Recombinase polymerase amplification (RPA) is a promising and emerging technology for rapidly amplifying target nucleic acid from minimally processed samples and through small portable instruments. RPA is suitable for point-of-care testing (POCT) and on-site field testing, and it is compatible with microfluidic devices. Several detection assays have been developed, but limited research has dug deeper into the chemistry of RPA to understand its kinetics and fix its shortcomings.

AREAS COVERED

This review provides a detailed introduction of RPA molecular mechanism, kits formats, optimization, application, pros, and cons. Moreover, this critical review discusses the nonspecificity issue of RPA, highlights its consequences, and emphasizes the need for more research to resolve it. This review discusses the reaction kinetics of RPA in relation to target length, product quantity, and sensitivity. This critical review also questions the novelty of recombinase-aided amplification (RAA). In short, this review discusses many aspects of RPA technology that have not been discussed previously and provides a deeper insight and new perspectives of the technology.

EXPERT OPINION

RPA is an excellent choice for pathogen detection, especially in low-resource settings. It has a potential to replace PCR for all purposes, provided its shortcomings are fixed and its reagent accessibility is improved.

Monitoring Pathogenic Viable E. coli O157:H7 in Food Matrices Based on the Detection of RNA Using Isothermal Amplification and a Paper-Based Platform

In recent years, the number of product recalls and contamination incidents involving pathogenic bacteria has significantly increased, and the ensuing infections continue to be an ongoing problem for public health and agriculture. Due to the widespread impact of these pathogens, there is a critical need for rapid, on-site assays that can provide rapid results. In this work, we demonstrate the development of a rapid and simple test based on the combination of reverse transcription with recombinase polymerase amplification followed by lateral flow strip detection of viable Escherichia coli O157:H7 cells by detecting the RNA of the pathogen. The optimized method can be performed for approximately 2 h with a detection limit of 10 CFU/mL of E. coli O157:H7 in buffer, spinach, and ground beef samples. Our assay is sensitive, detecting only E. coli O157:H7 and not nonpathogenic E. coli or other similar pathogens. This strategy was able to distinguish viable from nonviable bacteria and more significantly was able to detect viable but nonculturable bacteria, which is a major issue when using culture-based methods for monitoring pathogenic bacteria. An important advantage of this test is that it can provide timely identification and removal of contaminated consumables prior to distribution without an extensive sample preparation.

Rapid Detection of SARS-CoV-2 Using Duplex Reverse Transcription-Multienzyme Isothermal Rapid Amplification in a Point-of-Care Testing

In December 2019, a severe acute respiratory syndrome caused by SARS-CoV-2 spread rapidly worldwide. Portable nucleic acid tests of SARS-CoV-2 are critically important for diagnostics. In this study, we used an isothermal amplification method-Multienzyme Isothermal Rapid Amplification (MIRA)-for rapid detection of SARS-CoV-2. We designed the primers and probes in ORF1ab and N gene of SARS-CoV-2. The amplicons could be monitored by lateral flow dipsticks (LFDs). The reaction temperature, time, concentrations of primers and probes, and working volume were optimized. Four commercial swab collection buffers were used to test the amplification efficacy of our assay without RNA extraction. Our assay was able to amplify duplex targets of SARS-CoV-2 in one single reaction using one-step RT-MIRA. The assay worked well in a low volume of 10 μl at 38°C for 20 min. Using three collection buffers without guanidinium, our assay was able to amplify efficaciously without RNA extraction. The 95% limit of detection (LoD) of the RT-MIRA assay was 49.5 (95% CI, 46.8-52.7) copies/ml for ORF1ab gene and 48.8 (95% CI, 46.5-52.6) copies/ml for N gene. There is no cross-reaction with other human respiratory pathogens, such as SARS-CoV, MERS-CoV, influenza A virus, influenza B virus, human adenovirus, respiratory syncytial virus, human parainfluenza virus, and coronavirus 229E in our assay. The precision evaluation revealed that the C50-20% to C50+20% range bounds the C5-C95 interval. This assay also showed high anti-interference ability. The extraction-free RT-MIRA and qPCR detection results of 243 nucleic acid specimens from suspected patients or national references showed a 100.0% (95% confidence interval, 94.2%-100.0%) positive predictive value and a 100.0% (95% confidence interval, 92.7%-100.0%) negative predictive value. Compared with qPCR, the kappa value of the two assays was 1.00 (P < 0.0001). In conclusion, we provide a portable and visualized method for detection of SARS-CoV-2 without RNA extraction, allowing its application in SARS-CoV-2 on-site detection.

Reverse Transcription Recombinase Polymerase Amplification Assay for Rapid Detection of Avian Influenza Virus H9N2 HA Gene

The H9N2 subtype of avian influenza A virus (aIAV) is circulating among birds worldwide, leading to severe economic losses. H9N2 cocirculation with other highly pathogenic aIAVs has the potential to contribute to the rise of new strains with pandemic potential. Therefore, rapid detection of H9 aIAVs infection is crucial to control virus spread. A qualitative reverse transcription recombinase polymerase amplification (RT-RPA) assay for the detection of aIAV subtype H9N2 was developed. All results were compared to the gold standard (real-time reverse transcription polymerase chain reaction (RT-PCR)). The RT-RPA assay was designed to detect the hemagglutinin (HA) gene of H9N2 by testing three pairs of primers and a probe. A serial concentration between 10⁶ and 10⁰ EID₅₀ (50% embryo infective dose)/mL was applied to calculate the analytical sensitivity. The H9 RT-RPA assay was highly sensitive as the lowest concentration point of a standard range at one EID₅₀/mL was detected after 5 to 8 min. The H9N2 RT-RPA assay was highly specific as nucleic acid extracted from H9 negative samples and from other avian pathogens were not cross detected. The diagnostic sensitivity when testing clinical samples was 100% for RT-RPA and RT-PCR. In conclusion, H9N2 RT-RPA is a rapid sensitive and specific assay that easily operable in a portable device for field diagnosis of aIAV H9N2.

Biosensing strategies for the electrochemical detection of viruses and viral diseases - A review

Viruses are the causing agents for many relevant diseases, including influenza, Ebola, HIV/AIDS, and COVID-19. Its rapid replication and high transmissibility can lead to serious consequences not only to the individual but also to collective health, causing deep economic impacts. In this scenario, diagnosis tools are of significant importance, allowing the rapid, precise, and low-cost testing of a substantial number of individuals. Currently, PCR-based techniques are the gold standard for the diagnosis of viral diseases. Although these allow the diagnosis of different illnesses with high precision, they still present significant drawbacks. Their main disadvantages include long periods for obtaining results and the need for specialized professionals and equipment, requiring the tests to be performed in research centers. In this scenario, biosensors have been presented as promising alternatives for the rapid, precise, low-cost, and on-site diagnosis of viral diseases. This critical review article describes the advancements achieved in the last five years regarding electrochemical biosensors for the diagnosis of viral infections. First, genosensors and aptasensors for the detection of virus and the diagnosis of viral diseases are presented in detail regarding probe immobilization approaches, detection methods (label-free and sandwich), and amplification strategies. Following, immunosensors are highlighted, including many different construction strategies such as label-free, sandwich, competitive, and lateral-flow assays. Then, biosensors for the detection of viral-diseases-related biomarkers are presented and discussed, as well as point of care systems and their advantages when compared to traditional techniques. Last, the difficulties of commercializing electrochemical devices are critically discussed in conjunction with future trends such as lab-on-a-chip and flexible sensors.

Rapid Detection of Pathogens in Wound Exudate via Nucleic Acid Lateral Flow Immunoassay

The rapid detection of pathogens in infected wounds can significantly improve the clinical outcome. Wound exudate, which can be collected in a non-invasive way, offers an attractive sample material for the detection of pathogens at the point-of-care (POC). Here, we report the development of a nucleic acid lateral flow immunoassay for direct detection of isothermally amplified DNA combined with fast sample preparation. The streamlined protocol was evaluated using human wound exudate spiked with the opportunistic pathogen Pseudomonas aeruginosa that cause severe health issues upon wound colonization. A detection limit of 2.1 × 10⁵ CFU per mL of wound fluid was achieved, and no cross-reaction with other pathogens was observed. Furthermore, we integrated an internal amplification control that excludes false negative results and, in combination with the flow control, ensures the validity of the test result. The paper-based approach with only three simple hands-on steps has a turn-around time of less than 30 min and covers the complete analytical process chain from sample to answer. This newly developed workflow for wound fluid diagnostics has tremendous potential for reliable pathogen POC testing and subsequent target-oriented therapy.

One-Step Reverse-Transcription Recombinase Polymerase Amplification Using Lateral Flow Strips for the Detection of Coxsackievirus A6

Hand, foot, and mouth disease (HFMD) is a common infectious disease affecting mainly children under 5 years of age. Coxsackievirus A6 (CVA-6), a major causative pathogen of HFMD, has caused outbreaks in recent years. Currently, no effective vaccine or antiviral treatments are available. In this study, one-step reverse-transcription recombinase polymerase amplification (RT-RPA), combined with a disposable lateral flow strip (LFS) assay, was developed to detect CVA-6. This assay can be performed in less than 35 min at 37°C without expensive instruments, and the result can be observed directly with the naked eye. The sensitivity of the RT-RPA-LFS was 10 copies per reaction, which was comparable to that of the conventional real-time quantitative polymerase chain reaction (qPCR) assays. Moreover, the assay specificity was 100%. The clinical performance of the RT-RPA-LFS assay was evaluated using 142 clinical samples, and the coincidence rate between RT-RPA-LFS and qPCR was 100%. Therefore, our RT-RPA-LFS assay provides a simple and rapid approach for point-of-care CVA-6 diagnosis.

A critical review of point-of-care diagnostic technologies to combat viral pandemics

The COVID-19 global pandemic of 2019-2020 pointedly revealed the lack of diagnostic solutions that are able to keep pace with the rapid spread of the virus. Despite the promise of decades of lab-on-a-chip research, no commercial products were available to deliver rapid results or enable testing in the field at the onset of the pandemic. In this critical review, we assess the current state of progress on the development of point-of-care technologies for the diagnosis of viral diseases that cause pandemics. While many previous reviews have reported on progress in various lab-on-a-chip technologies, here we address the literature from the perspective of the testing needs of a rapidly expanding pandemic. First, we recommend a set of requirements to heed when designing point-of-care diagnostic technologies to address the testing needs of a pandemic. We then review the current state of assay technologies with a focus on isothermal amplification and lateral-flow immunoassays. Though there is much progress on assay development, we argue that the largest roadblock to deployment exists in sample preparation. We summarize current approaches to automate sample preparation and discuss both the progress and shortcomings of these developments. Finally, we provide our recommendations to the field of specific challenges to address in order to prepare for the next pandemic.

Advances in the Diagnosis of Foot-and-Mouth Disease

Foot-and-mouth disease (FMD) is a devastating livestock disease caused by foot-and-mouth disease virus (FMDV). Outbreaks of this disease in a country always result in conspicuous economic losses to livestock industry and subsequently lead to serious socioeconomic damages due to the immediate imposition of trade embargo. Rapid and accurate diagnoses are imperative to control this infectious virus. In the current review, enzyme-linked immunosorbent assay (ELISA)-based methods used in FMD diagnosis are extensively reviewed, particularly the sandwich, liquid-phase blocking, and solid-phase competition ELISA. The differentiation of infected animals from vaccinated animals using ELISA-based methods is also highlighted, in which the role of 3ABC polyprotein as a marker is reviewed intensively. Recently, more studies are focusing on the molecular diagnostic methods, which detect the viral nucleic acids based on reverse transcription-polymerase chain reaction (RT-PCR) and RT-loop-mediated isothermal amplification (RT-LAMP). These methods are generally more sensitive because of their ability to amplify a minute amount of the viral nucleic acids. In this digital era, the RT-PCR and RT-LAMP are progressing toward the mobile versions, aiming for on-site FMDV diagnosis. Apart from RT-PCR and RT-LAMP, another diagnostic assay specifically designed for on-site diagnosis is the lateral flow immunochromatographic test strips. These test strips have some distinct advantages over other diagnostic methods, whereby the assay often does not require the aid of an external device, which greatly lowers the cost per test. In addition, the on-site diagnostic test can be easily performed by untrained personnel including farmers, and the results can be obtained in a few minutes. Lastly, the use of FMDV diagnostic assays for progressive control of the disease is also discussed critically.

Applying a Linear Amplification Strategy to Recombinase Polymerase Amplification for Uniform DNA Library Amplification

Recombinase polymerase amplification (RPA) is an isothermal DNA amplification method with broad applications as a point-of-care test and in molecular biology techniques. Currently, most of the applications are focused on target-specific amplification. Because RPA has the advantage of amplifying DNA under isothermal conditions, we utilized RPA as a DNA library amplification tool. In this study, we used a sheared genomic DNA library and an oligonucleotide (oligo) library for the comparison of polymerase chain reaction and RPA. For the sheared DNA library, we observed biased amplification after RPA was conducted. Thus, to amplify the size-variable DNA library uniformly, we introduced a linear amplification strategy with RPA and successfully improved the uniformity. On the other hand, using the same-sized oligo library, we confirmed that RPA amplified this library uniformly without modification of the protocol. These results demonstrate that RPA can be applied not only to amplify a specific target as previously demonstrated but also to amplify a complex DNA library composed of a large number of different DNA molecules.

Visual signal generation for the detection of influenza viruses by duplex recombinase polymerase amplification with lateral flow dipsticks

We present a detailed study on visual detection of influenza viruses by duplex recombinase polymerase amplification (RPA) with lateral flow dipsticks (LFDs). The LFD consisted of two test lines and a control line, on which anti-fluorescein isothiocyanate antibodies, anti-digoxigenin antibodies, and biotinylated bovine serum albumin were immobilized, respectively. The performance of the LFD was evaluated with dual-labeled DNA amplicons. The results indicate that the detection of DNA amplicons by LFDs is specific and sensitive, with detection limits of 5.80 fmol for fluorescein isothiocyanate-labeled amplicons and 8.39 fmol for digoxigenin-labeled amplicons. We next developed a duplex RPA-LFD assay for simultaneous detection of influenza A virus and influenza B virus, and then optimized the parameters, including the reaction temperature, reaction time, and concentrations of primers and probes. Assessment of the specificity and sensitivity indicated that this assay is sensitive and specific for simultaneous detection of influenza viruses, with detection limits of 50 copies per reaction for influenza B virus and 500 copies per reaction for influenza A virus, without cross-reactivity with other pathogens. Compared with real-time PCR as a reference method to detect influenza viruses in clinical samples, the clinical sensitivity of the duplex RPA-LFD assay was 78.57% for influenza A virus and 87.50% for influenza B virus, with 100% specificity. In conclusion, the duplex RPA-LFD assay is a rapid, cost-effective, and sensitive method for the identification of influenza viruses.