Development of a CRISPR/Cas12a-recombinase polymerase amplification assay for visual and highly specific identification of the Congo Basin and West African strains of mpox virus

Development of a single-tube RPA/CRISPR-cas12a detection platform for monkeypox virus

Monkeypox is a zoonotic disease caused by the monkeypox virus (MPXV), with outbreaks primarily occurring in West and Central Africa. The recent global MPXV outbreak underscores the urgent need for effective detection methods. Currently, qPCR is considered the gold standard for MPXV detection; however, it requires specialized personnel and costly equipment. This study introduces a CRISPR-Cas12a-based detection system targeting the MPXV A27L gene, achieving a detection limit as low as 10 aM. This system exhibits high specificity, with no cross-reactivity with other orthopoxviruses, and delivers results in under 40 min. To support point-of-care testing (POCT), we developed a lateral flow assay (LFA) strip for easy result visualization. The detection system was validated using six different clinical sample types, revealing that herpes fluid and saliva are the most suitable sources. The findings of this study align with qPCR results. Additionally, we lyophilized the RPA and CRISPR reagents to improve transport, storage, and field deployment. In conclusion, this study presents a reliable molecular diagnostic approach for early MPXV detection and point-of-care testing, contributing to epidemic prevention and control.

Leveraging CRISPR-Cas-Enhanced Isothermal Amplification Tools for Quick Identification of Pathogens Causing Livestock Diseases

Prompt and accurate diagnosis of infectious pathogens of livestock origin is of utmost importance for epidemiological surveillance and effective therapeutic strategy formulation. Among various methods, nucleic acid-based detection of pathogens is the most sensitive and specific; but the majority of these assays need expensive equipment and skilled workers. Due to the rapid advancement of clustered regularly interspaced short palindromic repeats-CRISPR-associated protein (CRISPR-Cas)-based nucleic acid detection methods, these are now being widely used for pathogen detection. CRISPR-Cas is a bacterial counterpart of "adaptive immunity", generally used for editing genome. Many CRISPR systems have been modified for nucleic acid detection due to their excellent selectivity in detecting DNA and RNA sequences. The combination of CRISPR with suitable isothermal amplification technologies has made it more sensitive, specific, versatile, and reproducible for the detection of pathogen nucleic acids at the point of care. Amplification of pathogen nucleic acid by isothermal amplification followed by CRISPR-Cas-based detection has several advantages, including short sample-to-answer times and no requirement for laboratory set-up. They are also significantly less expensive than the existing nucleic acid detection methods. This review focuses on the recent trends in the use of this precision diagnostic method for diagnosis of a wide range of animal pathogens with or without zoonotic potential, particularly various isothermal amplification strategies, and visualization methods for sensing bacteria, viruses, and parasites of veterinary and public health importance.

Rapid detection of feline parvovirus using RAA-CRISPR/Cas12a-based lateral flow strip and fluorescence

Feline parvovirus (FPV) causes severe gastroenteritis and leukopenia in cats, with high morbidity and mortality, necessitating a rapid and effective antigen diagnostic test with high sensitivity and specificity. In this study, a diagnostic platform based on a combination of Recombinase-Aided Amplification (RAA) and CRISPR/Cas12a was established for detecting FPV. Cas12a recombinant protein was purified using Nickel-Nitriloacetic Acid resin after heterologous expression in Escherichia coli. The results of RAA-CRISPR/Cas12a can be detected with a fluorescence reader or lateral flow strips (LFS) for on-site detection. The RAA-CRISPR/Cas12a-LFS had a detection limit of 2.1 × 100 copies of recombinant plasmids per reaction, compared with 2.1 × 103 copies for conventional PCR analysis. Furthermore, no cross-reactivity was observed for the RAA-CRISPR/Cas12a assay with feline coronavirus, feline herpesvirus, and feline calicivirus, demonstrating reasonable specificity. Additionally, 43 cat fecal samples with suspected clinical signs were assayed with RAA-CRISPR/Cas12a-LFS and conventional PCR in parallel. The RAA-CRISPR/Cas12a-LFS showed a 100% coincident rate with PCR. In summary, a novel, visual, sensitive, and specific detection assay based on RAA and CRISPR/Cas12a was developed for FPV.

Facilitating self-testing with a fast, accurate, and simplified shelf-stable colorimetric LAMP system for Mpox and SARS-CoV-2 detection

The rapid and accurate detection of viral infections is essential for effective disease management and prevention. Quantitative polymerase chain reaction (qPCR) remains the gold standard for viral detection due to its high sensitivity and specificity. However, its limitations-including the need for specialized equipment, trained personnel, and longer processing times-make it impractical for at-home or rapid testing. Although numerous point-of-care assays based on isothermal nucleic acid amplification have been developed, they often lack the simplicity and adaptability required for self-testing in non-laboratory settings such as at home. To address this, we developed and validated the SCOLAR (Shelf-stable Colorimetric LAMP system for Rapid self-testing of viruses) system, a simplified, portable, and accurate diagnostic tool designed for self-testing of Mpox and SARS-CoV-2 infections. The SCOLAR system employs novel lyophilized colorimetric loop-mediated isothermal amplification (LAMP) beads, a customized sample lysis buffer, and smartphone-assisted RGB color analysis for interpreting results. Validation was conducted using 24 mock Mpox skin swabs, 32 wastewater samples, and 104 clinical SARS-CoV-2 nasopharyngeal swabs, with comparisons to an in-house qPCR assay. The SCOLAR system demonstrated an analytical sensitivity of below 10 copies/μL for all targets within 15 min. Diagnostic performance for mock Mpox samples exhibited 93.8 % sensitivity and 100 % specificity, while wastewater samples achieved 100 % sensitivity and specificity. SARS-CoV-2 swabs had 96 % sensitivity and 100 % specificity. The system also proved effective for self-testing by untrained individuals. SCOLAR offers a reliable, easy-to-use platform for rapid self-testing, with potential for broader applications in public health strategies to enhance pandemic preparedness and response.

The current status and future prospects of CRISPR-based detection of monkeypox virus: A review

BACKGROUND

The current pandemic of 2022 global mpox (formerly known as monkeypox), caused by infection with monkeypox virus (MPXV), has now reached over 120 countries. This constitutes a critical public health issue requiring effective disease management and surveillance. Rapid and reliable diagnosis is conducive to the control of infection, early intervention, and timely treatment. Clinical laboratories use various conventional diagnostic methods for detecting MPXV, including PCR, which can be regarded as a gold-standard diagnostic method. However, the application of PCR is limited by its requirements for high-cost equipment, skilled professionals, and a laboratory setting.

RESULTS

Clustered regularly interspaced short palindromic repeats (CRISPR)-based diagnostic systems have provided promising prospects for the rapid, sensitive, and specific detection of infectious diseases, especially in point-of-care settings. Over the past 2 years, an increasing number of researchers have concentrated on the application of the CRISPR method to mpox diagnosis. In the majority of cases, a two-step method was chosen, with CRISPR/Cas12a and recombinase polymerase amplification (RPA) as pre-amplification methods, followed by a fluorescence readout. Different strategies have been applied to overcome the encountered limitations of CRISPR detection, but no consensus on an integrated solution has been achieved. Thus, the application of the CRISPR/Cas system in mpox detection requires further exploration and improvement.

SIGNIFICANCE

This review discusses contemporary studies on MPXV CRISPR detection systems and the strategies proposed to address the challenges faced by CRISPR diagnosis with the hope of helping the development of CRISPR detection methods and improving pathogen detection technologies.

CRISPR/Cas13a combined with reverse transcription and RPA for NoV GII.4 monitoring in water environments

Water bodies contaminated with the norovirus (NoV) are important vectors for its transmission. Therefore, enhanced monitoring of NoV in aqueous environments plays an active role in preventing diseases. Here, we reverse transcribed viral RNA into cDNA, and then used the constructed RPA-CRISPR/Cas13a-based platform for sensitive and quantitative monitoring of NoV GII.4 in aqueous environments. The use of glycerol as a phase separator and the direct release of nucleic acids from the virus by NaOH significantly enhanced the stability of the assay and reduced its economic cost. This assay is sensitive, specific, and stable. Based on the qualitative detection method, we established a relatively accurate quantitative detection method using the plasmid as a standard. Four water samples, totaling 64 samples, were analyzed using this method and compared with the qPCR method. The results of the two methods showed 100 % concordance with no significant difference in viral load. The entire process of our established method-from viral nucleic acid extraction to the output of the results-was completed in 30 min, much less than the time required for qPCR method. This suggests that the assay can be used as an alternative to qPCR for monitoring the change of NoV GII.4 concentration in water bodies, and shows high potential for application in the immediate detection of viruses in aqueous environments and resource-limited areas.

Loop-mediated isothermal amplification linked a nanoparticles-based biosensor for detecting Epstein-Barr virus

Epstein-Barr virus (EBV) is a ubiquitous gamma herpesvirus that maintains a lifelong latent association with B lymphocytes. Here, a rapid and reliable diagnosis platform for detecting EBV infection, employing loop-mediated isothermal amplification (LAMP) combined with a gold nanoparticles-based lateral flow biosensors (AuNPs-LFB) (termed LAMP Amplification Mediated AuNPs-LFB Detection, LAMAD), was developed in the current study. A set of specific LAMP primers targeting the Epstein-Barr nuclear antigen (EBNA) leader protein (EBNA-LP) gene was designed and synthesized. Subsequently, these templates extracted from various pathogens and whole blood samples were used to optimize and evaluate the EBV-LAMAD assay. As a result, the limit of detection (LoD) of the EBV-LAMAD assay was 45 copies/reaction. The EBV-LAMAD assay can detect all representative EBV pathogens used in the study, and of note, no cross-reactions were observed with other non-EBV organisms. Moreover, the whole workflow of the EBV-LAMAD assay can be completed within 70 min, including rapid EBV template preparation, EBV-LAMP amplification, and AuNPs-LFB-mediated detection. Taken together, the EBV-LAMAD assay targeting the EBNA-LP gene is a rapid, simplified, sensitive, reliable, and easy-to-use detection protocol that can be used as a competitive potential diagnostic/screening tool for EBV infection in clinical settings, especially in basic laboratories in resource-limited regions. KEY POINTS: • A novel, simplified, and easy-to-use AuNPs-LFB biosensor was designed and prepared. • LAMP combined with an AuNPs-LFB targeting the novel EBNA-LP gene was established. • EBV-LAMAD is a rapid, sensitive, and reliable detection protocol for EBV infection.

CRISPR-based strategies for sample-to-answer monkeypox detection: current status and emerging opportunities

The global health threat posed by the Monkeypox virus (Mpox) requires swift, simple, and accurate detection methods for effective management, emphasizing the growing necessity for decentralized point-of-care (POC) diagnostic solutions. The clustered regularly interspaced short palindromic repeats (CRISPR), initially known for its effective nucleic acid detection abilities, presents itself as an attractive diagnostic strategy. CRISPR offers exceptional sensitivity, single-base specificity, and programmability. Here, we reviewed the latest developments in CRISPR-based POC devices and testing strategies for Mpox detection. We explored the crucial role of genetic sequencing in designing crRNA for CRISPR reaction and understanding Mpox transmission and mutations. Additionally, we showed the integration of CRISPR-Cas12 strategy with pre-amplification and amplification-free methods. Our study also focused on the significant role of Cas12 proteins and the effectiveness of Cas12 coupled with recombinase polymerase amplification (RPA) for Mpox detection. We envision the future prospects and challenges, positioning CRISPR-Cas12-based POC devices as a frontrunner in the next generation of molecular biosensing technologies.

Advances and challenges of mpox detection technology

Mpox is a zoonotic disease caused by the monkeypox virus (MPXV). Diagnosing and treating the disease has become a global health concern requiring close attention to its spread to non-endemic regions. Clinical diagnosis is based on laboratory test results. Conventional detection techniques include real-time quantitative polymerase chain reaction (qPCR), genome sequencing, antigen and antibody identification, and virus isolation. Nevertheless, these methods fall short of rapidly and efficiently identifying MPXV, as they require specialized training, specific laboratory environments, and professional-grade equipment. Emerging technologies offer complementary advantages to meet diverse diagnostic needs, including various point-of-care testing (POCT) approaches and integrating biosensors with rapid detection techniques. This review discusses prospective future research avenues for MPXV detection, examining the advances and challenges of various detection techniques which may contribute to the ongoing elimination of mpox human-to-human transmission and serves as a reference for developing effective prevention and control strategies.

Rapid detection of monkeypox virus and differentiation of West African and Congo Basin strains using endonuclease restriction-mediated real-time PCR-based testing

The ongoing multi-country outbreak of monkeypox virus (MPXV) has continuously attracted global attention, highlighting the critical need for timely and accurate methods to detect MPXV and differentiate its clades. Herein, we devised a novel multiplex ET-PCR (endonuclease restriction-mediated real-time PCR) assay that integrates PCR amplification, restriction endonuclease cleavage and real-time fluorescence detection to diagnose MPXV infection and distinguish the Congo Basin and West African MPXV strains. In the MPXV ET-PCR system, three sets of specific primers were designed for MPXV, Congo Basin and West African strains. A short sequence, which could be recognized by restriction endonuclease enzyme BstUI, was added to the 5'end of amplification primers. Then, the modified primers were assigned different reporter dyes and corresponding quenching dyes to each of the three targets, enabling real-time fluorescence reporting of the results and multiplex detection. The designed assay enabled the detection of single or three targets in a single tube, with excellent specificity and analytical sensitivity in terms of plasmid and pseudotyped virus. Moreover, the clinical feasibility of our assay was validated using artificially simulated plasma, nasopharyngeal swab and skin swab samples. In conclusion, the multiplex ET-PCR assay devised here had the advantages of simple primer design, cost-effectiveness, low contamination risk, excellent sensitivity, high specificity and multiplex detection, making it a valuable and dependable tool for curbing the extensive spread of MPXV.

A modified multiple cross displacement amplification linked with a gold nanoparticle biosensor for the detection of Epstein-Barr virus in clinical applications

Epstein-Barr virus (EBV), a double-stranded DNA virus belonging to the family Herpesviridae, infects more than 95% of healthy adults by attacking the host immune system. Here, a novel detection protocol, utilizing the modified multiple cross displacement amplification (MCDA) technique combined with a gold nanoparticles-based lateral flow biosensors (AuNPs-LFB), was devised and developed to detect EBV infection (termed EBV-MCDA-LFB assay). Ten MCDA primers targeting the EBNA-LP gene were designed, including CP1* primers modified with 6-carboxyfluorescein (FAM) and D1* primers modified with biotin. Then, nucleic acid templates extracted from various pathogens and whole blood samples were used to optimize and evaluate the EBV-MCDA-LFB assay. As a result, the lowest concentration of EBNA-plasmids, which can be detected by MCDA-LFB assay with an optimal reaction condition of 67°C for 30 min, was 10 copies/reaction. Here, the MCDA-LFB assay can detect all EBV pathogens used in the study, and no cross-reactions with non-EBV organisms were observed. Meanwhile, the entire detection workflow of the EBV-MCDA-LFB assay for whole blood samples, including DNA template preparation (25 min), EBV-MCDA amplification (30 min), and AuNPs-LFB-mediated validation (2-5 min), can be completed within 1 h. Taken together, the EBV-MCDA-LFB assay established in the current study is a rapid, simplified, sensitive, specific, and easy-to-obtain technique that can be used as a screening or diagnostic tool for EBV infection in clinical applications, especially in resource-poor regions.