Detection of Babesia gibsoni in dogs by combining recombinase polymerase amplification (RPA) with lateral flow (LF) dipstick

Current status of recombinase polymerase amplification technologies for the detection of pathogenic microorganisms

Rapid detection of pathogenic microorganisms is key to the epidemiologic identification, prevention and control of disease in the field of public health. PCR-based pathogen detection methods have been widely used because they overcome the time-consuming issues encountered in traditional culture-based methods, including the limited detecting window-phase of immunological detection. However, the requirement for precise temperature-controlled thermal cyclers severely limits the application of these methods in resource-limited areas. Recombinase polymerase amplification (RPA) is a new type of nucleic acid amplification technology that can amplify DNA or RNA at a constant temperature. It has the advantages of simple operation, high specificity and sensitivity and a short detection time. In recent years, a number of alternative methods for pathogenic microorganism detection have been developed by combining microfluidic technology with RPA. Through the design of chip structures, optimization of injection modes, and utilization of multiple detection and quantification methods, the integration of pathogen nucleic acid extraction, amplification and detection is achieved, and this approach is suitable for the rapid detection of pathogenic microorganisms in various environments. In this review, we compare different nucleic acid amplification techniques, explain the principle of RPA technology, detection methods, and applications for pathogen microorganism detection and describe future direction of RPA application. These methods increase the ability to rapidly screen pathogenic microorganisms, thus improving the management of infectious diseases in the field of public health.

Advanced approaches for the diagnosis and chemoprevention of canine vector-borne pathogens and parasites-Implications for the Asia-Pacific region and beyond

Vector-borne pathogens (VBPs) of canines are a diverse range of infectious agents, including viruses, bacteria, protozoa and multicellular parasites, that are pernicious and potentially lethal to their hosts. Dogs across the globe are afflicted by canine VBPs, but the range of different ectoparasites and the VBPs that they transmit predominate in tropical regions. Countries within the Asia-Pacific have had limited prior research dedicated to exploring the epidemiology of canine VBPs, whilst the few studies that have been conducted show VBP prevalence to be high, with significant impacts on dog health. Moreover, such impacts are not restricted to dogs, as some canine VBPs are zoonotic. We reviewed the status of canine VBPs in the Asia-Pacific, with particular focus on nations in the tropics, whilst also investigating the history of VBP diagnosis and examining recent progress in the field, including advanced molecular methods, such as next-generation sequencing (NGS). These tools are rapidly changing the way parasites are detected and discovered, demonstrating a sensitivity equal to, or exceeding that of, conventional molecular diagnostics. We also provide a background to the armoury of chemopreventive products available for protecting dogs from VBP. Here, field-based research within high VBP pressure environments has underscored the importance of ectoparasiticide mode of action on their overall efficacy. The future of canine VBP diagnosis and prevention at a global level is also explored, highlighting how evolving portable sequencing technologies may permit diagnosis at point-of-care, whilst further research into chemopreventives will be essential if VBP transmission is to be effectively controlled.

Sensitive and rapid detection of Babesia species in dogs by recombinase polymerase amplification with lateral flow dipstick (RPA-LFD)

Canine babesiosis is a tick-borne disease caused by Babesia spp., which infects and destroys healthy erythrocytes, leading to mortality and morbidity in dogs. The diagnosis of babesiosis is tedious and time-consuming, especially in latent and chronic infections. Here, a recombinase polymerase amplification combined with a lateral flow dipstick (RPA-LFD) assay was developed for rapid and accurate detection of Babesia spp. in canine blood specimens based on the 18S rRNA region. The RPA-LFD assay using rpaBab264 gave specificity to Babesia spp. in dogs (B. vogeli and B. gibsoni) without cross-amplification to other parasites (apicomplexans and non-apicomplexans), with detection limit of at least 22.5 copies/μl (0.1 fg/µl) at 40 °C for at least 10 min. The whole process of DNA amplification by RPA and readout by LFD did not exceed 30 min. To determine the performance of the RPA-LFD assay, a total of 30 clinical samples was examined and compared with conventional PCR (cPCR) and multiplex HRM (mHRM). Eight dogs (26.67%) were detected as positive by RPA-LFD, while seven and six were found positive by cPCR and mHRM, respectively. RPA-LFD and cPCR showed high agreement with Babesia spp. detection with kappa > 0.9. We confirmed that the dogs were infected by B. vogeli from sequences of positive PCR results. Our findings suggested that RPA-LFD using the rpaBab264 assay offered a rapid, accurate, cost-effective and simple method for Babesia spp. detection that is feasibly applicable to be rapid kit at a pet hospital or point-of-care testing.

Recombinase polymerase amplification in the molecular diagnosis of microbiological targets and its applications

Since the introduction of the polymerase chain reaction (PCR) technique in 1983, nucleic acid amplification has permeated all fields of biological science, particularly clinical research. Despite its importance, PCR has been restricted to specialized centers and its use in laboratories with few resources is limited. In recent decades, there has been a notable increase in the development of new isothermal technologies for molecular diagnosis with the hope of overcoming the traditional limitations of the laboratory. Among these technologies, recombinase polymerase amplification (RPA) has a wide application potential because it does not require thermocyclers and has high sensitivity, specificity, simplicity, and detection speed. This technique has been used for DNA and RNA amplification in various pathogenic organisms such as viruses, bacteria, and parasites. In addition, RPA has been successfully implemented in different detection strategies, making it a promising alternative for performing diagnoses in environments with scarce resources and a high burden of infectious diseases. In this study, we present a review of the use of RPA in clinical settings and its implementation in various research areas.

Recombinase polymerase amplification with lateral flow strip for detecting Babesia microti infections

Babesia microti is one of the most important pathogens causing humans and rodents babesiosis-an emerging tick-borne disease that occurs worldwide. At present, the gold standard for the detection of Babesia is the microscopic examination of blood smears, but this diagnostic test has several limitations. The recombinase polymerase amplification with lateral flow (LF-RPA) assay targeting the mitochondrial cytochrome oxidase subunit I (cox I) gene of B. microti was developed in this study. The LF-RPA can be performed within 10-30 min, at a wide range of temperatures between 25 and 45 °C, which is much faster and easier to perform than conventional PCR. The results showed that the LF-RAP can detect 0.25 parasites/μl blood, which is 40 times more sensitive than the conventional PCR based on the V4 variable region of 18S rRNA. Specificity assay showed no cross-reactions with DNAs of related apicomplexan parasites and their host. The applicability of the LF-RPA method was further evaluated using two clinical human samples and six experimental mice samples, with seven samples were positively detected, while only three of them were defined as positive by conventional PCR. These results present the developed LF-RPA as a new simple, specific, sensitive, rapid and convenient method for diagnosing infection with B. microti. This novel assay was the potential to be used in field applications and large-scale sample screening.

Highly Sensitive Detection of Low-Abundance BRAF V600E Mutation in Fine-Needle Aspiration Samples by Zip Recombinase Polymerase Amplification

Papillary thyroid carcinoma (PTC) is the most common thyroid cancer with high incidence in endocrine tumors, which emphasizes the significance of accurate diagnostics. Still, the commonly used cytological method (fine-needle aspiration (FNA) cytology) and molecular diagnostic methods (such as PCR and sequencing) are limited in terms of diagnostic time, sensitivity, and user-friendliness. In this study, we introduce a novel Zip recombinase polymerase amplification (Z-RPA) strategy to efficiently detect rare mutant alleles in PTC fine-needle aspiration samples, which is sensitive, fast, and simple to manipulate. Using Zip nucleic acid (ZNA) probes to clamp the mutation region, the phi 29 polymerase could selectively displace mismatched ZNA probes and start amplification, while leaving complementary ZNA probes untouched and blocking amplification according to genotype. We demonstrated the good sensitivity and specificity of this strategy with optimized conditions and design, which enabled detection of BRAF V600E mutation in a total 4 ng of genomic DNA within 40 min (≈1 copy). Robust behavior in clinical specimen analysis was also demonstrated. The Z-RPA strategy provides a pragmatic approach to rapidly, sensitively, and easily detect BRAF V600E mutation in clinical fine-needle aspiration samples, which is a promising method for early cancer diagnosis and treatment guideline.

Isothermal Detection of Canine Blood Parasite (Ehrlichia canis) Utilizing Recombinase Polymerase Amplification Coupled with Graphene Oxide Quenching-Based Pyrrolidinyl Peptide Nucleic Acid

Canine monocytic ehrlichiosis (CME), caused by transmitted Ehrlichia canis infection, is a major disease in dogs with worldwide distribution. Herein, a nucleic acid assay was established for the identification of E. canis infection employing a fluorescently labeled conformationally constrained pyrrolidinyl PNA probe (Flu-acpcPNA) designed to sequence-specifically target the 16S rRNA gene. The sensing principle is based on the excellent quenching ability of graphene oxide (GO) of the free PNA probe, that was diminished upon binding to the DNA target. The addition of DNase I improved the performance of the detection system by eliminating the nonspecific quenching capability of long-chain dsDNA and thus enhancing the fluorescence signaling. The assay was coupled with a recombinase polymerase amplification (RPA) technique, which could be performed under isothermal conditions (37 °C) without DNA denaturation and purification steps. The established method is simple to set up and execute, proving a rapid, specific, and sensitive detection of 16S rRNA gene of E. canis with a limit of detection at least 11.1 pM. This technique shows good potential for the visual detection of double-stranded DNA targets without the need for PCR or complicated instruments, which shows great promise for practical usage in resource limited areas.

Detection of Prorocentrum minimum by hyperbranched rolling circle amplification coupled with lateral flow dipstick

A novel method referred to as hyperbranched rolling circle amplification (HRCA) coupled with lateral flow dipstick (LFD) (HRCA-LFD) here was developed for specific, sensitive, rapid, and simple detection of Prorocentrum minimum. HRCA-LFD relies on a padlock probe (PLP) consisting of a common ligation sequence, two terminal sequences that complement the target DNA, and a manually designed detection probe (LFD probe). The two terminal sequences of the PLP were designed against the species-specific sites of the large subunit ribosomal DNA (LSU rDNA) D1-D2 region of P. minimum. The optimum parameters for HRCA were as follows: PLP concentration of 20 pM, ligation time of 30 min, ligation temperature of 59 °C, enzymic digestion time of 105 min, amplification time of 45 min, and amplification temperature of 58 °C. The HRCA-LFD displaying high specificity could accurately distinguish P. minimum from other microalgae. The detection limit of HRCA-LFD was as low as 1.42 × 10^-7 ng μL^-1 for genomic DNA, 1.03 × 10^-7 ng μL^-1 (approximately 27 copies) for recombinant plasmid containing the inserted LSU rDNA D1-D2, and 0.17 cells for crude DNA extract of P. minimum, which was consistently 100 times more sensitive than regular PCR. Interfering test suggested that the performance of HRCA-LFD is stable and would not be affected by other non-target species. The HRCA-LFD results of field samples that are comparable with microscopic examination confirmed that the developed method is competent for detection of target cells in field samples. In conclusion, the developed HRCA-LFD exhibiting stable performance is specific, sensitive, and rapid, which provides a good alternative to traditional microscopic examination for the detection of P. minimum cells in field samples.

Rapid isothermal duplex real-time recombinase polymerase amplification (RPA) assay for the diagnosis of equine piroplasmosis

Equine piroplasmosis (EP) is a severe disease of horses caused by the tick-borne protozoa Theileria equi (T. equi) and Babesia caballi (B. caballi). Infectious carriers are not always symptomatic, meaning there is a risk to non-enzootic areas. Regulatory tests for EP include sero-epidemiological methods for equine babesiosis, but these lack specificity due to cross-reactivity with other Babesia species. In this study, we present a real-time quantitative recombinase polymerase amplification (qRPA) method for fast simultaneous detection of both T. equi and B. caballi. In this method, primers and probes targeting the 18S rRNA gene of both T. equi and B. caballi, the ema-1 gene of T. equi and the bc48 gene of B. caballi were designed and evaluated. The sensitivity of qRPA was evaluated using the pUC57 plasmid DNA containing the target gene. For the pUC57-bc48 gene DNA, the R² value was 0.983 for the concentration range 0.2 ng (4.1 × 10⁷ DNA copies) to 2.0 fg (4.1 × 10¹ DNA copies). For the pUC57-ema gene DNA, the R² value was 0.993 for the concentration range 0.2 ng (5.26 × 10⁷ DNA copies) to 2.0 fg (5.26 × 10² DNA copies). For the pUC57-Bc18S gene DNA the R² value was 0.976 for the concentration range 2.0 ng (4.21 × 10⁸ DNA copies) to 2.0 fg (4.21 × 10² DNA copies). For the pUC57-Te18S gene DNA, the R² value was 0.952 (Fig. S3b) for the concentration range 2.0 ng (4.16 × 10⁸ DNA copies) to 2.0 fg (4.16 × 10² DNA copies). Furthermore, a duplex qRPA analysis was developed and optimized and the results showed that primers and probes targeting for the bc48 gene of B. caballi and the 18S rRNA gene of T. equi is the best combination for a duplex qRPA analysis in one reaction. The developed duplex qRPA assay has good specificity, and had negative amplification for several similar parasite. For DNA extracted from real horse blood specimens, this qRPA method has comparable sensitivity to traditional qPCR, but a simpler and more rapid operating process to obtain positive amplification. The qRPA, including the duplex strategy described here, could allow fast identification of the EP-causing T. equi and B. caballi, showing great potential for on-site EP screening of horses.

A novel PCR-based point-of-care method enables rapid, sensitive and reliable diagnosis of Babesia gibsoni infection in dogs

BACKGROUND

Babesia gibsoni (B. gibsoni) is an intraerythrocytic protozoan parasite of dogs that causes fever and hemolytic illness. A timely diagnosis is essential for the disease management.

RESULTS

Here, we report a QubeMDx PCR system which enables a rapid, sensitive and reliable diagnosis of B. gibsoni near the dog patient. Within 30 min, this diagnostic assay was able to detect as low as 0.002% parasitemia of the dog blood. Using clinical samples, this new assay was validated to demonstrate 100% agreement with real-time PCR.

CONCLUSIONS

This novel diagnostic method provides a reliable point-of-care test to assist in the identification of B. gibsoni.

Development of a recombinase polymerase amplification assay with lateral flow dipstick for rapid detection of feline parvovirus

Feline panleukopenia caused by feline parvovirus (FPV), a single-stranded DNA virus, is typically highly contagious and often presents with lethal syndrome. The broad spectrum of possible hosts suggests its potential for transmission from animal to person through close contact with pets. FPV thus serves as an example of the importance of new rapid point-of-care field diagnostic tools for the control and prevention of transmission, especially among rare wild animals and pet cats. Recombinase polymerase amplification (RPA), as a real-time and isothermal method, could be a more affordable alternative to PCR when combined with a lateral flow dipstick (LFD) indicator. In this study, we report a novel FPV lateral flow dipstick RPA (LFD-RPA) instant detection method capable of detecting a range of different FPV strains. The LFD-RPA assay consists of specific primers, probe, and nucleic acid strip. It is capable of detecting 10² copies of target nucleic acid per reaction, which is one order of magnitude higher than the sensitivity of traditional PCR. The most suitable reaction conditions for this assay are at 38 ℃ for 15 min. This paper develops an efficient visual detection system that can eliminate the need for professional staff and expensive and sophisticated equipment for field detection.