Development of a recombinase polymerase amplification lateral flow assay for the detection of active Trypanosoma evansi infections

Recombinase polymerase amplification combined with lateral flow dipstick assay for rapid visual detection of A.simplex (s. s.) and A.pegreffii in sea foods

Anisakiasis is a food-borne parasitic disease mainly caused by the third stage of Anisakis simplex (s. s.) and Anisakis pegreffii. Traditional methods for detecting of Anisakis involve morphology identification such as visual inspection, enzyme digestion, and molecular methods based on PCR, but they have certain limitations. In this study, the internal transcribed spacer 1 (ITS 1) regions of Anisakis were targeted to develop a visual screening method for detecting A. simplex (s. s.) and A. pegreffii in fish meat based on recombinase polymerase amplification (RPA) combined with lateral flow dipstick (LFD). Specific primers and probes were designed and optimized for temperature, reaction time, and detection threshold. LFD produced clear visual results that were easily identifiable after a consistent incubation of 10-20 min at 37 °C. The whole process of DNA amplification by RPA and readout by LFD did not exceed 30 min. In addition, the detection limit is up to 9.5 × 10-4 ng/μL, and the detection of the artificially contaminated samples showed that the developed assay can effectively and specifically detect A. simplex (s. s.) and A. pegreffii, which fully meet the market's requirements for fish food safety supervision.

Recent Progress in the Detection of Surra, a Neglected Disease Caused by Trypanosoma evansi with a One Health Impact in Large Parts of the Tropic and Sub-Tropic World

Surra is a wasting disease triggered by infection with Trypanosoma evansi, a protozoan blood parasite that causes mortality and morbidity in a broad spectrum of wild and domestic animals and occasionally humans. Trypanosoma evansi has the widest geographical spread among all pathogenic trypanosomes, inflicting significant worldwide economic problems due to its adverse effects on meat and milk production. For diagnosis, most endemic countries continue to rely on traditional parasitological and serological techniques, such as the analysis of blood smears by microscopy and the Card Agglutination Test for T. evansi (CATT/T. evansi). Although these techniques suffer from a limited positive predictive value (PPV), resource constraints in endemic countries often hinder the adoption of more advanced diagnostic tools such as PCR. This paper addresses diverse diagnostic approaches for identifying T. evansi and assesses their viability in field settings. Moreover, it underscores the urgency of transitioning towards molecular diagnostic techniques such as Loop-Mediated Isothermal Amplification (LAMP) and Recombinase Polymerase Amplification (RPA) for dependable high-PPV point-of-care (POC) diagnostics. Finally, this review delves into strategies to enhance and refine next-generation diagnostics for Surra as part of a One Health approach.

Recent advances in recombinase polymerase amplification: Principle, advantages, disadvantages and applications

After the outbreak of SARS-CoV-2, nucleic acid testing quickly entered people's lives. In addition to the polymerase chain reaction (PCR) which was commonly used in nucleic acid testing, isothermal amplification methods were also important nucleic acid testing methods. Among several common isothermal amplification methods like displaced amplification, rolling circle amplification, and so on, recombinase polymerase amplification (RPA) was recently paid more attention to. It had the advantages like a simple operation, fast amplification speed, and reaction at 37-42°C, et al. So it was very suitable for field detection. However, there were still some disadvantages to RPA. Herein, our review mainly summarized the principle, advantages, and disadvantages of RPA. The specific applications of RPA in bacterial detection, fungi detection, virus detection, parasite detection, drug resistance gene detection, genetically modified food detection, and SARS-CoV-2 detection were also described. It was hoped that the latest research progress on RPA could be better delivered to the readers who were interested in RPA.

Recent progress in diagnosis and treatment of Human African Trypanosomiasis has made the elimination of this disease a realistic target by 2030

Human African Trypanosomiasis (HAT) is caused by unicellular flagellated protozoan parasites of the genus Trypanosoma brucei. The subspecies T. b. gambiense is mainly responsible for mostly chronic anthroponotic infections in West- and Central Africa, accounting for roughly 95% of all HAT cases. Trypanosoma b. rhodesiense results in more acute zoonotic infections in East-Africa. Because HAT has a two-stage pathogenesis, treatment depends on clinical assessment of patients and the determination whether or not parasites have crossed the blood brain barrier. Today, ultimate confirmation of parasitemia is still done by microscopy analysis. However, the introduction of diagnostic lateral flow devices has been a major contributor to the recent dramatic drop in T. b. gambiense HAT. Other techniques such as loop mediated isothermal amplification (LAMP) and recombinant polymerase amplification (RPA)-based tests have been published but are still not widely used in the field. Most recently, CRISPR-Cas technology has been proposed to improve the intrinsic diagnostic characteristics of molecular approaches. This will become crucial in the near future, as preventing the resurgence of HAT will be a priority and will require tools with extreme high positive and negative predicted values, as well as excellent sensitivity and specificity. As for treatment, pentamidine and suramin have historically been the drugs of choice for the treatment of blood-stage gambiense-HAT and rhodesiense-HAT, respectively. For treatment of second-stage infections, drugs that pass the blood brain barrier are needed, and melarsoprol has been effectively used for both forms of HAT in the past. However, due to the high occurrence of post-treatment encephalopathy, the drug is not recommended for use in T. b. gambiense HAT. Here, a combination therapy of eflornithine and nifurtimox (NECT) has been the choice of treatment since 2009. As this treatment requires IV perfusion of eflornithine, efforts were launched in 2003 by the drugs for neglected disease initiative (DNDi) to find an oral-only therapy solution, suitable for rural sub-Saharan Africa treatment conditions. In 2019 this resulted in the introduction of fexinidazole, with a treatment regimen suitable for both the blood-stage and non-severe second-stage T. b. gambiense infections. Experimental treatment of T. b. rhodesiense HAT has now been initiated as well.

The COMBAT project: controlling and progressively minimizing the burden of vector-borne animal trypanosomosis in Africa

Vector-borne diseases affecting livestock have serious impacts in Africa. Trypanosomosis is caused by parasites transmitted by tsetse flies and other blood-sucking Diptera. The animal form of the disease is a scourge for African livestock keepers, is already present in Latin America and Asia, and has the potential to spread further. A human form of the disease also exists, known as human African trypanosomosis or sleeping sickness. Controlling and progressively minimizing the burden of animal trypanosomosis (COMBAT) is a four-year research and innovation project funded by the European Commission, whose ultimate goal is to reduce the burden of animal trypanosomosis (AT) in Africa. The project builds on the progressive control pathway (PCP), a risk-based, step-wise approach to disease reduction or elimination. COMBAT will strengthen AT control and prevention by improving basic knowledge of AT, developing innovative control tools, reinforcing surveillance, rationalizing control strategies, building capacity, and raising awareness. Knowledge gaps on disease epidemiology, vector ecology and competence, and biological aspects of trypanotolerant livestock will be addressed. Environmentally friendly vector control technologies and more effective and adapted diagnostic tools will be developed. Surveillance will be enhanced by developing information systems, strengthening reporting, and mapping and modelling disease risk in Africa and beyond. The socio-economic burden of AT will be assessed at a range of geographical scales. Guidelines for the PCP and harmonized national control strategies and roadmaps will be developed. Gender equality and ethics will be pivotal in all project activities. The COMBAT project benefits from the expertise of African and European research institutions, national veterinary authorities, and international organizations. The project consortium comprises 21 participants, including a geographically balanced representation from 13 African countries, and it will engage a larger number of AT-affected countries through regional initiatives.

The COMBAT project: controlling and progressively minimizing the burden of vector-borne animal trypanosomosis in Africa

Vector-borne diseases affecting livestock have serious impacts in Africa. Trypanosomosis is caused by parasites transmitted by tsetse flies and other blood-sucking Diptera. The animal form of the disease is a scourge for African livestock keepers, is already present in Latin America and Asia, and has the potential to spread further. A human form of the disease also exists, known as human African trypanosomosis or sleeping sickness. Controlling and progressively minimizing the burden of animal trypanosomosis (COMBAT) is a four-year research and innovation project funded by the European Commission, whose ultimate goal is to reduce the burden of animal trypanosomosis (AT) in Africa. The project builds on the progressive control pathway (PCP), a risk-based, step-wise approach to disease reduction or elimination. COMBAT will strengthen AT control and prevention by improving basic knowledge of AT, developing innovative control tools, reinforcing surveillance, rationalizing control strategies, building capacity, and raising awareness. Knowledge gaps on disease epidemiology, vector ecology and competence, and biological aspects of trypanotolerant livestock will be addressed. Environmentally friendly vector control technologies and more effective and adapted diagnostic tools will be developed. Surveillance will be enhanced by developing information systems, strengthening reporting, and mapping and modelling disease risk in Africa and beyond. The socio-economic burden of AT will be assessed at a range of geographical scales. Guidelines for the PCP and harmonized national control strategies and roadmaps will be developed. Gender equality and ethics will be pivotal in all project activities. The COMBAT project benefits from the expertise of African and European research institutions, national veterinary authorities, and international organizations. The project consortium comprises 21 participants, including a geographically balanced representation from 13 African countries, and it will engage a larger number of AT-affected countries through regional initiatives.

Development of a Lateral Flow Strip-Based Recombinase-Aided Amplification for Active Chlamydia psittaci Infection

Chlamydia psittaci is the causative agent of psittacosis, a worldwide zoonotic disease. A rapid, specific, and sensitive diagnostic assay would be benefit for C. psittaci infection control. In this study, an assay combining recombinase-aided amplification and a lateral flow strip (RAA-LF) for the detection of active C. psittaci infection was developed. The RAA-LF assay targeted the CPSIT_RS02830 gene of C. psittaci and could be accomplished in 15 min at a single temperature (39°C). The analytical sensitivity of the assay was as low as 1 × 100 copies/μl and no cross-reaction with some other intracellular pathogens was observed. Moreover, all feces samples from mice infected with C. psittaci at day-1 post-infection were positive in the RAA-LF assay. In conclusion, the RAA-LF assay provides a convenient, rapid, specific and sensitive method for detection of active C. psittaci infection and it is also suitable for C. psittaci detection in field.

A review of applications of environmental DNA for reptile conservation and management

Reptile populations are in decline globally, with total reptile abundance halving in the past half century, and approximately a fifth of species currently threatened with extinction. Research on reptile distributions, population trends, and trophic interactions can greatly improve the accuracy of conservation listings and planning for species recovery, but data deficiency is an impediment for many species. Environmental DNA (eDNA) can detect species and measure community diversity at diverse spatio‐temporal scales, and is especially useful for detection of elusive, cryptic, or rare species, making it potentially very valuable in herpetology. We aim to summarize the utility of eDNA as a tool for informing reptile conservation and management and discuss the benefits and limitations of this approach. A literature review was conducted to collect all studies that used eDNA and focus on reptile ecology, conservation, or management. Results of the literature search are summarized into key discussion points, and the review also draws on eDNA studies from other taxa to highlight methodological challenges and to identify future research directions. eDNA has had limited application to reptiles, relative to other vertebrate groups, and little use in regions with high species richness. eDNA techniques have been more successfully applied to aquatic reptiles than to terrestrial reptiles, and most (64%) of studies focused on aquatic habitats. Two of the four reptilian orders dominate the existing eDNA studies (56% Testudines, 49% Squamata, 5% Crocodilia, 0% Rhynchocephalia). Our review provides direction for the application of eDNA as an emerging tool in reptile ecology and conservation, especially when it can be paired with traditional monitoring approaches. Technologies associated with eDNA are rapidly advancing, and as techniques become more sensitive and accessible, we expect eDNA will be increasingly valuable for addressing key knowledge gaps for reptiles.

Molecular Analysis of Trypanosome Infections in Algerian Camels

PURPOSE

Surra is an economically important livestock disease in many low- and middle-income countries, including those of Northern Africa. The disease is caused by the biting fly-transmitted subspecies Trypanosoma brucei evansi, which is very closely related to the tsetse-transmitted subspecies T. b. brucei and the sexually transmitted subspecies T. b. equiperdum. At least two phylogenetically distinct groups of T. b. evansi can be distinguished, called type A and type B. These evolved from T. b. brucei independently. The close relationships between the T. brucei subspecies and the multiple evolutionary origins of T. b. evansi pose diagnostic challenges.

METHODS

Here we use previously established and newly developed PCR assays based on nuclear and mitochondrial genetic markers to type the causative agent of recent trypanosome infections of camels in Southern Algeria.

RESULTS/CONCLUSION

We confirm that these infections have been caused by T. b. evansi type A. We also report a newly designed PCR assay specific for T. b. evansi type A that we expect will be of diagnostic use for the community.

Recombinase Polymerase Amplification Combined with Real-Time Fluorescent Probe for Mycoplasma pneumoniae Detection

Mycoplasma pneumoniae (M. pneumoniae) is one of the major causes of community-acquired pneumonia, accounting for 20-40% of total cases. Rapid and accurate detection of M. pneumoniae is crucial for the diagnosis and rational selection of antibiotics. In this study, we set up a real-time recombinase polymerase amplification (RPA) assay to detect the conserved gene CARDS of M. pneumoniae. The amplification can be finished in 20 min at a wide temperature range from 37-41 °C. The limit of detection of RPA assay was 10 fg per microliter. Cross-reaction with commonly detected respiratory pathogens was not observed using RPA assay. Among clinical sputum samples, the detection rate of RPA assay and real-time PCR assay was 48.4% (92/190) and 46.3% (88/190), respectively (p = 0.68). Therefore, the RPA assay for M. pneumoniae detection is rapid and easy to use and may serve as a promising test for early diagnosis of M. pneumoniae infection.

Salivarian Trypanosomes Have Adopted Intricate Host-Pathogen Interaction Mechanisms That Ensure Survival in Plain Sight of the Adaptive Immune System

Salivarian trypanosomes are extracellular parasites affecting humans, livestock and game animals. Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense are human infective sub-species of T. brucei causing human African trypanosomiasis (HAT—sleeping sickness). The related T. b. brucei parasite lacks the resistance to survive in human serum, and only inflicts animal infections. Animal trypanosomiasis (AT) is not restricted to Africa, but is present on all continents. T. congolense and T. vivax are the most widespread pathogenic trypanosomes in sub-Saharan Africa. Through mechanical transmission, T. vivax has also been introduced into South America. T. evansi is a unique animal trypanosome that is found in vast territories around the world and can cause atypical human trypanosomiasis (aHT). All salivarian trypanosomes are well adapted to survival inside the host’s immune system. This is not a hostile environment for these parasites, but the place where they thrive. Here we provide an overview of the latest insights into the host-parasite interaction and the unique survival strategies that allow trypanosomes to outsmart the immune system. In addition, we review new developments in treatment and diagnosis as well as the issues that have hampered the development of field-applicable anti-trypanosome vaccines for the implementation of sustainable disease control.

New Haplotypes of Trypanosoma evansi Identified in Dromedary Camels from Algeria

PURPOSE

Surra is a zoonotic disease caused by Trypanosoma evansi (Trypanozoon), a salivary trypanosome native to Africa which affects a wide range of mammals worldwide and causes mortality and significant economic loss. The present study was devoted to the molecular characterization of T. evansi derived from naturally infected dromedary camels in Algeria.

METHODS

A total of 148 blood samples were collected from mixed age camels living in one of four geographic regions (Ouargla, El Oued, Biskra and Ghardaia) of Algeria. Samples underwent PCR amplification and sequencing of the internal transcribed spacer 1 (ITS1) complete sequence.

RESULTS

DNA of Trypanosoma spp. was found in 19 camels (12.84%). Trypanosoma spp. molecular positivity was not affected by sex (p = 0.50), age (p = 0.08), or geographic location (p = 0.12). Based on multiple sequence alignment of the obtained DNA sequences with representative T. evansi ITS1 sequences available globally, the Algerian sequences were grouped within four different haplotypes including two which were original.

CONCLUSION

Results of this study provide preliminary data on which future studies of genetic diversity and molecular epidemiology of T. evansi can be based.

Bushmeat Species Identification: Recombinase Polymerase Amplification (RPA) Combined with Lateral Flow (LF) Strip for Identification of Formosan Reeves' Muntjac (Muntiacus reevesi micrurus)

Simple Summary

Illegal hunting of wild animals and the consumption of bushmeat are recognized not only as a threat to biodiversity, but also as a risk for transmitting zoonotic diseases. Illegal sales of meat products from Formosan Reeves’ muntjac (Muntiacus reevesi micrurus) is a growing issue in Taiwan, bringing forth the demand for a fast and cost-effective technique for meat species identification. In this study, a new recombinase polymerase amplification combined with a lateral flow strip to identify Formosan Reeves’ muntjac in meat products was described. This method only requires minimal sample preparation and an isothermal heating process. The result can be interpreted by the naked eye within 30 min. The system we designed efficiently detected a variety of meat products, and no cross-reactions were observed with other animal species. This simple assay provides a sensitive and specific method to identify bushmeat sources in various meat products, which holds the potential for on-field application in the future.

Abstract

The identification of animal species of meat in meat products is of great concern for various reasons, such as public health, religious beliefs, food allergies, legal perspectives, and bushmeat control. In this study, we developed a new technique to identify Formosan Reeves’ muntjac in meat using recombinase polymerase amplification (RPA) in combination with a lateral flow (LF) strip. The DNA extracted from a piece of Formosan Reeves’ muntjac meat was amplified by a pair of specific primers based on its mitochondrial cytochrome b gene for 10 min at a constant temperature ranging from 30 to 45 °C using RPA. Using the specific probe added to the RPA reaction system, the amplified products were visualized on the LF strip within 5 min. The total operating time from quick DNA extraction to visualizing the result was approximately 30 min. The RPA-LF system we designed was efficient when using boiled, pan-fried, roasted, stir-fried, or stewed samples. The advantages of simple operation, speediness, and cost-effectiveness make our RPA-LF method a promising molecular detection tool for meat species identification of either raw or variously cooked Formosan Reeves’ muntjac meat. It is also possible to apply this method to identify the meat of other wildlife sources.

An Unbiased Immunization Strategy Results in the Identification of Enolase as a Potential Marker for Nanobody-Based Detection of Trypanosoma evansi

Trypanosoma evansi is a widely spread parasite that causes the debilitating disease “surra” in several types of ungulates. This severely challenges livestock rearing and heavily weighs on the socio-economic development in the affected areas, which include countries on five continents. Active case finding requires a sensitive and specific diagnostic test. In this paper, we describe the application of an unbiased immunization strategy to identify potential biomarkers for Nanobody (Nb)-based detection of T. evansi infections. Alpaca immunization with soluble lysates from different T. evansi strains followed by panning against T. evansi secretome resulted in the selection of a single Nb (Nb11). By combining Nb11-mediated immuno-capturing with mass spectrometry, the T. evansi target antigen was identified as the glycolytic enzyme enolase. Four additional anti-enolase binders were subsequently generated by immunizing another alpaca with the recombinant target enzyme. Together with Nb11, these binders were evaluated for their potential use in a heterologous sandwich detection format. Three Nb pairs were identified as candidates for the further development of an antigen-based assay for Nb-mediated diagnosis of T. evansi infection.