背景:传统上使用Kato-Katz方法和福尔马林乙酸乙酯浓缩技术来诊断Opisthorchisviverrini感染。然而,这些技术的有限的灵敏度和特异性促使人们探索各种分子方法,如常规聚合酶链反应(PCR)和实时PCR,检测O.Viverrini感染.最近,开发了一种称为重组酶聚合酶扩增(RPA)-成簇的规则间隔短回文重复序列(CRISPR)/CRISPR相关蛋白(Cas)(RPA-CRISPR/Cas)测定的新技术,作为检测各种病原体的即时工具。包括病毒和细菌,如严重急性呼吸道综合症冠状病毒2和结核分枝杆菌。该技术表现出高灵敏度和特异性。因此,我们开发并使用RPA-CRISPR/Cas测定法检测现场收集的人类粪便中的O.viverrini感染。
方法:为了检测粪便样本中的O.viverrini感染,我们开发了CRISPR/Cas12a(RNA指导的核酸内切酶)系统与RPA(Ov-RPA-CRISPR/Cas12a)组合。几个粪便样本,蠕虫阳性和蠕虫阴性,用于扩增条件的开发和优化,CRISPR/Cas检测条件,检测限,以及RPA-CRISPR/Cas12a检测O.Viverrini感染的特异性。使用基于荧光值的实时PCR系统确定检测结果。此外,当记者被贴上荧光素的标签时,使用紫外线(UV)透射仪目视检查检测结果。接收器工作特征曲线(ROC)用于确定荧光检测的最佳截止值。诊断性能,包括敏感性和特异性,在与标准方法比较的基础上评估Ov-RPA-CRISPR/Cas12a测定。
结果:Ov-RPA-CRISPR/Cas12a分析显示出检测O.viverriniDNA的高特异性。根据检测限,该测定法可以使用实时PCR系统以低至10-1ng的浓度检测O.viverriniDNA。然而,在这种方法中,在紫外光下目视检查需要的最小浓度为1ng。为了验证Ov-RPA-CRISPR/Cas12a测定,分析了121个现场收集的粪便样品。显微镜检查显示,29个样品对O.viverrini样鸡蛋呈阳性。其中,根据Ov-RPA-CRISPR/Cas12a测定和显微镜检查确认18为真阳性,而11个样本仅通过显微镜检查确定为阳性,表明其他微小肠吸虫感染的可能性。
结论:本研究中开发的Ov-RPA-CRISPR/Cas12a测定法可以成功检测现场收集的粪便中的O.viverrini感染。由于本研究中报道的测定的高特异性,它可以用作确认O.Viverrini感染的替代方法,标志着即时诊断发展的第一步。
BACKGROUND: Opisthorchis viverrini infection is traditionally diagnosed using the Kato-Katz method and formalin ethyl-acetate concentration technique. However, the limited sensitivity and specificity of these techniques have prompted the exploration of various molecular approaches, such as conventional polymerase chain reaction (PCR) and real-time PCR, to detect O. viverrini infection. Recently, a novel technique known as recombinase polymerase amplification (RPA)-clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) (RPA-CRISPR/Cas) assay was developed as a point-of-care tool for the detection of various pathogens, including viruses and bacteria such as severe acute respiratory syndrome coronavirus 2 and Mycobacterium tuberculosis. This technology has demonstrated high sensitivity and specificity. Therefore, we developed and used the RPA-CRISPR/Cas assay to detect O. viverrini infection in field-collected human feces.
METHODS: To detect O. viverrini infection in fecal samples, we developed a CRISPR/Cas12a (RNA-guided endonuclease) system combined with RPA (Ov-RPA-CRISPR/Cas12a). Several fecal samples, both helminth-positive and helminth-negative, were used for the development and optimization of amplification conditions, CRISPR/Cas detection conditions, detection limits, and specificity of the RPA-CRISPR/Cas12a assay for detecting O. viverrini infection. The detection results were determined using a real-time PCR system based on fluorescence values. Additionally, as the reporter was labeled with fluorescein, the detection results were visually inspected using an ultraviolet (UV) transilluminator. A receiver operating characteristic curve (ROC) was used to determine the optimal cutoff value for fluorescence detection. The diagnostic performance, including sensitivity and specificity, of the Ov-RPA-CRISPR/Cas12a assay was evaluated on the basis of comparison with standard methods.
RESULTS: The Ov-RPA-CRISPR/Cas12a assay exhibited high specificity for detecting O. viverrini DNA. On the basis of the detection limit, the assay could detect O. viverrini DNA at concentrations as low as 10-1 ng using the real-time PCR system. However, in this method, visual inspection under UV light required a minimum concentration of 1 ng. To validate the Ov-RPA-CRISPR/Cas12a assay, 121 field-collected fecal samples were analyzed. Microscopic examination revealed that 29 samples were positive for O. viverrini-like eggs. Of these, 18 were confirmed as true positives on the basis of the Ov-RPA-CRISPR/Cas12a assay and microscopic examination, whereas 11 samples were determined as positive solely via microscopic examination, indicating the possibility of other minute intestinal fluke infections.
CONCLUSIONS: The Ov-RPA-CRISPR/Cas12a assay developed in this study can successfully detect O. viverrini infection in field-collected feces. Due to the high specificity of the assay reported in this study, it can be used as an alternative approach to confirm O. viverrini infection, marking an initial step in the development of point-of-care diagnosis.