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RT-RPA Assisted CRISPR/Cas12a Based One-Pot Rapid and Visual Detection of the Pan-Dengue Virus.

Globally ≤ 4 billion of the population are at potential risk of contracting dengue virus (DENV) infection. Seasonal outbreaks of dengue are frequently reported causing a high healthcare burden. Undiagnosed DENV can lead to severe morbidity and mortality. Early diagnosis of DENV relies on molecular methods, which are impractical in resource-constrained settings (RCSs). Dengue can be caused by any of the four distinct DENV serotypes. Therefore, a simple method for rapid diagnosis of Pan-DENV serotypes is of utmost importance at RCSs. A fluorescence detection platform for Pan-DENV using RT-RPA and CRISPR/Cas12a was developed targeting nonstructural 1 (NS1) gene for DENV-1, 2, and 3, and envelope (E) gene for DENV-2. Further, crRNA specific to DENV serotypes were designed to facilitate CRISPR/Cas12a detection. Analytical sensitivity was determined using synthetic RNA and DENV serotypes genome. Clinical validation of the assay was performed using RNA extracted from AES/AFI clinical samples. The developed CRISPR/Cas12a-based detection platform can detect all four serotypes of DENV viz 1-4 in a single pot using fluorescence detection. This assay showed the limit of detection ≥ 781 zg reaction- 1, ≥ 1.81 ag reaction-1, ≥ 62.5 fg reaction-1, and ≥ 2.5 pg reaction-1 for synthetic DENV-1, DENV-2, DENV-3, and DENV-4 template, respectively. Our assay demonstrated the analytic sensitivity of ≥ 10 ng reaction-1 for DENV-1 and DENV-4, and ≥ 0.5 ng reaction-1 for DENV-3 and DENV-4 genomes. This assay showed no cross-reactivity with other related etiologies tested causing AFI/AES. With 76 clinical samples (DENV PCR positive = 16, DENV PCR negative = 60), the assay demonstrated 93.7% sensitivity and 100% specificity with an overall accuracy of 98.7% for detection of the Pan-DENV serotypes. Our assay displayed comparable results to that of RT-PCR. The ease of interpretation and rapid detection of the Pan-DENV, represents the potential of the developed assay as an ideal point-of-care test. This assay upon field-deployment could help in reducing healthcare burden, provide differential diagnosis and support initiating early and prompt treatment to patients at RCS.

Dengue Virus

Sensitive and Visualized Detection of Hantavirus Using CRISPR/Cas12a Based on AutoCORDSv2 Design.

In recent years, detection technologies based on the CRISPR/Cas12a method have been extensively utilized in the fields of nucleic acid, enzyme, and macromolecule detection, thereby reinforcing their significant role in the detection landscape. Enhancing the simplicity of design, efficiency, and automation of the CRISPR/Cas12a detection system is essential for advancing its application in diagnostics. Recently, we developed an automated CRISPR/Cas12a design system named AutoCORDSv2. This system can process published genomic sequences of pathogenic bacteria in a high-throughput manner and automatically generate conserved and highly specific crRNA sequences, along with primer sequences for target amplification. This capability facilitates the specific and precise design of the CRISPR/Cas12a detection system. In this study, crRNAs targeting the Hantaan virus (HTNV) and Seoul virus (SEOV), as well as RT-PCR primers and RT-RPA primers, were designed using AutoCORDSv2. The experimental results demonstrated that the CRISPR/Cas12a system, automatically designed by AutoCORDSv2, was specific for the detection of both the HTNV and SEOV, with no cross-reactivity observed with other pathogens. The detection sensitivity reached 6 copies/μL (equivalent to 111 copies per amplification reaction), whether measured by a microplate reader or directly observed with the naked eye. The detection results for 50 samples were consistent with those obtained from commercial RT-qPCR kits, indicating high precision. Furthermore, the CRISPR/Cas12a system designed by AutoCORDSv2 can also be utilized for the development of a single-tube detection system with a sensitivity of 42 copies per reaction. This system combined with a 5-min extraction step and RT-RPA, further underscoring its potential for application.

CRISPR-Cas Systems

RT-RPA-Assisted CRISPR/Cas12a-Based Isothermal Detection of Chikungunya Virus.

Chikungunya virus (CHIKV) is transmitted through the bite of Aedes mosquitoes, specifically A. aegypti and A. albopictus. CHIKV belongs to the alphavirus with a positive-sense ssRNA genome of 11-12 kb size. The virus has been reported from various geographical regions across the globe. Chikungunya fever is an acute febrile illness, which, if left untreated, may develop into chronic arthralgia that may persist for several months or acute encephalitis syndrome. Therefore, early diagnosis of CHIKV is crucial to initiate prompt supportive treatment. Laboratory diagnosis of CHIKV typically relies on serological tests such as IgM antigen capture ELISA and molecular methods including RT-PCR or qRT-PCR. However, both these methods are not viable in peripheral settings. This chapter highlights recent advancements in molecular detection techniques for CHIKV, specifically isothermal detection methods that eliminate the requirement for complex instruments. The detection is facilitated by RT-RPA and CRISPR/Cas12a endonuclease. The assay offers advantages over existing methods such as rapid and early detection, and eliminates cross-over contamination, ultra-sensitivity, high specificity, and ease of result interpretation.

Chikungunya virus