Characterization of novel Leishmania infantum recombinant proteins encoded by genes from five families with distinct capacities for serodiagnosis of canine and human visceral leishmaniasis

Diagnostic Potential for the Detection of Canine Visceral Leishmaniasis of an ELISA Assay Based on the Q5 Recombinant Protein: A Large-Scale and Comparative Evaluation Using Canine Sera with a Positive Diagnosis from the Dual-Path-Platform (DPP) Test

Dogs are considered the major domestic reservoir for human visceral leishmaniasis, a serious disease caused by the Leishmania infantum parasite. Diagnosis of canine visceral leishmaniasis (CVL) is critical for disease control, with several methods currently available. Among the serological tests, the DPP rapid test and the EIE-LVC, more commonly used in Brazil, are associated with variable sensitivity and specificity. Research with novel recombinant proteins such as the ELISA with the recombinant chimeric protein Q5 may therefore improve the CVL diagnosis. This study aimed to evaluate the true diagnostic potential of Q5 in an ELISA assay using a large number of CVL-suspected sera (406) with a previous positive diagnosis based on the rapid DPP test. Sera from the DPP-positive dogs, also assessed with the EIE-LVC test, were compared with sera from healthy dogs (n = 46) and used for ELISA tests using the recombinant Q5. The resulting data as well as the correlation with the clinical signs and the environmental characteristics of the animals were analyzed using Medal and GraphPad Prism 8.0. Overall, similar levels of lower sensitivity (67-68%) were seen for both the commercial EIE-LVC test and the Q5 ELISA when all assessed sera were considered, but a much greater sensitivity (92%) was seen for those samples from symptomatic dogs only. In contrast, many negative results were observed for the DPP-positive sera from asymptomatic dogs or those with no clinical information available. A selection of those sera were tested yet again in new ELISA assays using a second batch of the recombinant Q5, purified under milder denaturing conditions, as well as using another recombinant protein (Lci13). The results reveal a higher-than-expected incidence of likely false-positive results for DPP, reinforcing the need for other recombinant proteins, such as the chimeric Q5, to be investigated as possible alternatives to the currently used CVL diagnostic methods.

Laboratory diagnostics for human Leishmania infections: a polymerase chain reaction-focussed review of detection and identification methods

Leishmania infections span a range of clinical syndromes and impact humans from many geographic foci, but primarily the world's poorest regions. Transmitted by the bite of a female sand fly, Leishmania infections are increasing with human movement (due to international travel and war) as well as with shifts in vector habitat (due to climate change). Accurate diagnosis of the 20 or so species of Leishmania that infect humans can lead to the successful treatment of infections and, importantly, their prevention through modelling and intervention programs. A multitude of laboratory techniques for the detection of Leishmania have been developed over the past few decades, and although many have drawbacks, several of them show promise, particularly molecular methods like polymerase chain reaction. This review provides an overview of the methods available to diagnostic laboratories, from traditional techniques to the now-preferred molecular techniques, with an emphasis on polymerase chain reaction-based detection and typing methods.

Early detection and persistent positivity of anti-Leishmania antibodies using a recombinant protein-based ELISA in naturally infected dogs in Brazil

Background

Visceral leishmaniasis (VL) is a zoonotic disease caused by Leishmania infantum, for which dogs constitute the main urban parasite reservoir. Control measures and the treatment of canine visceral leishmaniasis (CVL) are essential to reduce VL cases. Early and accurate detection of L. infantum-infected dogs is crucial to the success of VL control. To improve the serological detection of L. infantum-exposed dogs, we evaluated the early diagnosis capacity of a recombinant protein (rLci5) in an immunosorbent assay (ELISA) to detect naturally infected dogs. Additionally, we evaluated the persistence of the positive results obtained by rLci5 ELISA in comparison to other conventional diagnostic test methods.

Methods

Serum samples obtained from 48 L. infantum-infected dogs involved in a cohort study were evaluated using different diagnostic methods (qPCR, EIE-LVC, DPP-LVC and splenic culture). The results were compared to rLci5 ELISA to determine its capacity to diagnose L. infantum infection at earlier infection time points. The persistence of positive diagnostic test results was also compared for each dog evaluated.

Results

rLci5 ELISA presented higher rates of positive results at early time points compared to the other diagnostic tests employed in the cohort study, as early as 24 months prior to detection by other tests. rLci5 ELISA positivity was 52.1% (25/48) at baseline, while qPCR was 35.4% (17/48), DPP-LVC 27.1% (13/48), EIE-LVC 22.9% (11/48) and culture only 4.2% (2/48). In at least one of the time points of the 24-month cohort study, rLci5 ELISA was positive in 100% (48/48) of the dogs, versus 83% (40/48) for qPCR, 75% (36/48) for DPP-LVC, 65% (31/48) for EIE-LVC and 31% (15/48) for culture. Investigating clinical signs in association with diagnostic test positivity, rLci5 ELISA successfully detected CVL in 62.9% (95/151) of the clinical evaluations with a score of 0–3, 64.3% (45/70) with scores between 4 and 7, and 73.7% (14/19) with scores > 7, providing higher rates of positivity than all other methods evaluated. Moreover, rLci5 ELISA presented the greatest persistence with respect to test positivity: 45.8% of the dogs evaluated.

Conclusion

Four diagnostic tests were compared to rLci5 ELISA, which presented earlier infection diagnosis and a greater persistence of positive test results. Accordingly, the use of the rLci5 ELISA can improve CVL diagnostic performance by detecting infected dogs sooner than other testing methods, with enhanced persistence of positive results over the course of the infection.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04895-z.

Assessment of a recombinant protein from Leishmania infantum as a novel tool for Visceral Leishmaniasis (VL) diagnosis in VL/HIV co-infection cases

Visceral Leishmaniasis and HIV-AIDS coinfection (VL/HIV) is considered a life-threatening pathology when undiagnosed and untreated, due to the immunosuppression caused by both diseases. Serological tests largely used for the VL diagnosis include the direct agglutination test (DAT), ELISA and immunochromatographic (ICT) assays. For VL diagnosis in HIV infections, different studies have shown that the use of the DAT assay facilitates the VL diagnosis in co-infected patients, since the performance of the most widely used ELISA and ICT tests, based on the recombinant protein rK39, are much less efficient in HIV co-infections. In this scenario, alternative recombinant antigens may help the development of new serological diagnostic methods which may improve the VL diagnosis for the co-infection cases. This work aimed to evaluate the use of the recombinant Lci2 antigen, related to, but antigenically more diverse than rK39, for VL diagnosis in co-infected sera through ELISA assays. A direct comparison between recombinant Lci2 and rK39 was thus carried out. The two proteins were first tested using indirect ELISA with sera from VL afflicted individuals and healthy controls, with similar performances. They were then tested with two different sets of VL/HIV co-infected cases and a significant drop in performance, for one of these groups, was observed for rK39 (32% sensitivity), but not for Lci2 (98% sensitivity). In fact, an almost perfect agreement (Kappa: 0.93) between the Lci2 ELISA and DAT was observed for the coinfected VL/HIV patients. Lci2 then has the potential to be used as a new tool for the VL diagnosis of VL/HIV co-infections.

Genome mutations of the Turkish strain Leishmania infantum_TR01

PURPOSE

Today, almost 15 years have passed since the whole genome sequence (WGS) of a Leishmania parasite was completed for the first time. However, information on the genetics of these parasites remains to be elucidated. Genome-based studies may contribute to control strategies for leishmaniasis. The increase in genetically based studies, particularly whole-genome sequencing studies on Leishmania, will contribute to the control of leishmaniasis, which is a common and neglected disease worldwide. Our previous study obtained the Leishmania infantum_TR01 (Lin_TR01) genome sequence (Guldemir et al., 2020). In the present study, we focused on the mutations detected in the genome and aimed to investigate the effects of these mutations.

METHODS

In our previous study, the whole-genome sequence of the L. infantum_TR01 strain was obtained (Guldemir et al., 2020). In the present study, 3153 polymorphisms were detected in bioinformatics analysis performed on the Geneious 11.0.5. (www.geneious.com) platform. Herein, the L. infantum JPCM5 strain was used as the reference genome for genome mapping. Polymorphic regions were determined using the Find Variations/SNPs program on the Geneious platform. We further analyzed these polymorphisms detected in the previous study. Additionally, a literature review was performed by searching the PubMed database for proteins with polymorphisms.

RESULTS

In our previous study (Guldemir et al., 2020), the genomic DNA sequence was submitted to the NCBI GenBank (www.ncbi.nlm.nih.gov) database and registered under the name Leishmania infantum_TR01 (Lin_TR01) and project accession number PRJNA437593. As a result of the annotation of the genome, 3153 polymorphisms were identified. In this study, 166 protein-coding polymorphisms were found among the 3153 polymorphisms, affecting 63 different proteins. Fourteen of them were studied, and the remaining 49 proteins were not studied. The 14 proteins examined in terms of the mutations detected in this study were related to virulence (n = 5), vaccine candidates (n = 2), diagnosis/typing (n = 4), drug resistance (n = 2), drug targets (n = 3) and vital function (n = 1).

CONCLUSION

As mentioned previously, the acquisition of the Lin_TR01 genome was described in our previous study (Guldemir et al., 2020). The present meta-analytical study is the first comparison report of whole-genome sequence-based polymorphisms between the Turkish strain Leishmania infantum_TR01 and reference Leishmania infantum JPCM5 strain and evaluated polymorphisms and proteins. In this study, we focused on the mutations detected in the genome, and the effects of these mutations were investigated and evaluated together with the current literature. In our previous study, a high-quality WGS of Leishmania infantum was successfully obtained for the first time in Turkey (1). In this study, the comparison of both genomes will contribute to providing the scientific community with a solid infrastructure for postgenomic investigations of the parasite.

A Flow Cytometry-Based Serological Assay to Detect Visceral Leishmaniasis in HIV-Infected Patients

Visceral Leishmaniasis (VL) is a severe parasitic disease that has emerged as an important opportunistic condition in HIV-infected patients and whose control is impaired by inaccurate identification. This is mainly due to the serological tests used for VL having a reduced performance in cases of VL-HIV coinfection due to a low humoral response. In this situation, however, a positive test has even greater diagnostic value when combined with the clinical status. This study aimed to evaluate the application and performance of flow cytometry to detect anti-Leishmania infantum antibodies in HIV-infected patients. Sera from VL/HIV coinfected patients, characterized using "gold standard" techniques, were compared with sera from healthy controls plus sera from HIV-infected individuals. The flow cytometry results were expressed as levels of IgG reactivity, based on the percentage of positive fluorescent parasites (PPFP). A ROC curve analysis of a serum titration indicated a PPFP of 1.26% as being the cutoff point to segregate positive and negative results. At the 1:2,048 dilution, with 89% sensitivity and 83% specificity, flow cytometry showed greater sensitivity in relation to the serological tests evaluated. Futhermore, flow cytometry was the only assay that positively identified all VL-HIV patients with quantified HIV load. Together, these findings suggest that flow cytometry may be used as an alternative serological approach for VL identification and as a tool to characterize the humoral response against Leishmania infantum in HIV-infected patients.

Immunoprophylactic Potential of a New Recombinant Leishmania infantum Antigen for Canine Visceral Leishmaniasis: An In Vitro Finding

The development and application of safe and effective immunoprophylactic/immunotherapeutic agents against canine visceral leishmaniasis (CanL) have been pointed out as the only means for the real control of the disease. Thus, this study aimed to evaluate the in vitro cellular immune response of dogs, elicited by the new recombinant proteins of Leishmania infantum, Lci10 and Lci13, in order to investigate their potential for vaccinology. Twenty-four dogs were submitted to clinical, parasitological, serological and molecular tests, and then separated into two study groups: 12 infected (InD) and 12 non-infected dogs (NInD), and six of each group were directed for Lci10 and Lci13 evaluation. Peripheral blood mononuclear cells (PBMC) were cultured and stimulated with Lci10 (10 μg/ml) or Lci13 (5 μg/ml), and with L. infantum soluble antigen (LSA) (25 μg/ml) or no stimulus (NS) as controls. Afterwards, the mRNA levels of different cytokines were quantified through qPCR, and Nitric Oxide (NO) production was assessed in the culture supernatants. Significant differences were considered when p ≤ 0.05. The comparative analysis revealed that, in the NInD group, Lci13 promoted a significant increase in the expression of IFN-γ in relation to LSA (p = 0.0362), and the expression of this cytokine in NInD was significantly higher than that presented in the InD (p = 0.0028). A negative expression for TGF-β was obtained in both groups. Lci13 also induced a greater production of NO in relation to the NS sample in the NInD group. No significant differences were observed after stimulation with Lci10. In conclusion, the results suggest a protective role of Lci13 for uninfected animals, thus with a potential for immunoprophylaxis. The results will help to direct the antigen Lci13 for further studies (pre-clinical trials), in order to determine its immunogenicity and reactogenicity effects, as a way to consolidate its real applicability for vaccinology against CanL.

Recent advances and new strategies in Leishmaniasis diagnosis

Leishmaniasis is a set of complex and multifaceted syndromes, with different clinical manifestations, caused by different species of the genus Leishmania spp. that can be characterized by at least four syndromes: visceral leishmaniasis (VL, also known as kala-azar), post-kala-azar dermal leishmaniasis (PKDL), cutaneous leishmaniasis (CL), and mucocutaneous leishmaniasis (MCL). Among the most serious clinical forms, VL stands out, which causes the death of around 59,000 people annually. Fast and accurate diagnosis in VL is essential to reduce the disease's morbidity and mortality. There are a large number of diagnostic tests for leishmaniasis, however they do cross-react with other protozoa and their sensitivity changes according to the clinical form of the disease. Thus, it is essential and necessary to provide a diagnosis that is sufficiently sensitive to detect asymptomatic infected individuals and specific to discriminate individuals with other infectious and parasitic diseases, thus enabling more accurate diagnostic tools than those currently used. In this context, the aim of this review is to summarize the conventional diagnostic tools and point out the new advances and strategies on visceral and cutaneous leishmaniasis diagnosis.

Gene design, optimization of protein expression and preliminary evaluation of a new chimeric protein for the serological diagnosis of both human and canine visceral leishmaniasis

Background

Visceral leishmaniasis (VL) is a major neglected disease, potentially fatal, whose control is still impaired by inefficient and/or expensive treatment and diagnostic methods. The most promising approach for VL diagnosis uses serological assays with recombinant proteins, since they are more efficient and easier to perform. Tests developed for the human form of the disease, however, have not been shown to be efficient for its diagnosis in the canine host, the major reservoir for the American VL.

Methodology/Principal findings

Here, we describe a systematic approach aimed at the production of a new chimeric protein potentially able to be used for both human and canine VL diagnosis and based both on in silico gene design and experimental data. Starting from the previous identification of Leishmania infantum recombinant antigens efficient for the diagnosis of either human or canine VL, three of the best performing antigens were selected (Lci2, Lci3 and Lci12). After a preliminary evaluation validating the chimeric approach, DNA fragments encoding predicted antigenic regions from each protein, enriched with repeats, were joined in various combinations to generate a total of seventeen chimeric genes optimized for prokaryotic expression. These were assessed for optimal expression and purification yield, with four chimeric proteins being efficiently produced. Their diagnostic potential was then evaluated through ELISA assays with sera from VL afflicted humans and dogs. After two rounds of gene design, the results showed high levels of sensitivity for the best chimeric protein, named Q5, in humans (82%) and dogs (100%) with 100% specificity in comparison with healthy controls. A single non-specific reaction was seen with serum from individuals with tegumentary leishmaniasis.

Conclusion

The newly described chimeric protein is potentially useful for the detection of both humans and dogs afflicted with VL, with its use in rapid tests necessary for validation as a new diagnostic tool.

Visceral leishmaniasis (VL) is a major neglected disease, potentially fatal, caused mainly by Leishmania infantum and L. donovani. Its control is still impaired by inefficient and/or expensive treatment and diagnostic methods. VL diagnosis is mostly dependent on serological assays made with bacterially expressed Leishmania proteins. Tests developed for the human form of the disease, however, are not efficient for its diagnosis in the canine host. Dogs are the major reservoir for the American VL and their infection also needs to be monitored, requiring a distinct diagnostic test. Here, we describe a new chimeric protein potentially able to be used for both human and canine VL diagnosis. Based on a systematic approach using three Leishmania proteins known to be efficient for the diagnosis of either human or canine VL, fragments of each were joined in various combinations. The diagnostic potential of different chimeric proteins was then evaluated with human and canine sera from VL afflicted individuals. The best protein showed high levels of sensitivity in humans and dogs with no relevant false positive results with healthy controls or humans with tegumentary leishmaniasis. It is then potentially useful for the detection of both humans and dogs afflicted with VL in novel diagnostic tests.

Improving the serodiagnosis of canine Leishmania infantum infection in geographical areas of Brazil with different disease prevalence

Serodiagnosis of Leishmania infantum infection in dogs relies on the detection of antibodies against leishmanial crude extracts or parasitic defined antigens. The expansion of canine leishmaniasis from geographical areas of Brazil in which the infection is endemic to regions in which the disease is emerging is occurring. This fact makes necessary the analysis of the serodiagnostic capabilities of different leishmanial preparations in distinct geographical locations. In this article sera from dogs infected with Leishmania and showing the clinical form of the disease, were collected in three distinct Brazilian States and were tested against soluble leishmanial antigens or seven parasite individual antigens produced as recombinant proteins. We show that the recognition of soluble leishmanial antigens by sera from these animals was influenced by the geographical location of the infected dogs. Efficacy of the diagnosis based on this crude parasite preparation was higher in newly endemic regions when compared with areas of high disease endemicity. We also show that the use of three of the recombinant proteins, namely parasite surface kinetoplastid membrane protein of 11 kDa (KMP-11), and two members of the P protein family (P2a and P0), can improve the degree of sensitivity without adversely affecting the specificity of the diagnostic assays for canine leishmaniasis, independently of the geographical area of residence. In addition, sera from dogs clinically healthy but infected were also assayed with some of the antigen preparations. We demonstrate that the use of these proteins can help to the serodiagnosis of Leishmania infected animals with subclinical infections. Finally, we propose a diagnostic protocol using a combination of KMP-11, P2a y P0, together with total leishmanial extracts.

Production of a kinesin-related recombinant protein (Lbk39) from Leishmania braziliensis by Leishmania tarentolae promastigotes and its application in the serodiagnosis of leishmaniasis

The leishmaniases are multifactorial zoonotic diseases requiring a multidisciplinary One Health approach for diagnosis and control. For leishmaniasis diagnosis, here we describe production of a new recombinant protein based on a kinesin-related gene of Leishmania braziliensis (Lbk39), which shows 59% amino acid identity to the L. infantum homologue. The Lbk39 gene was synthesized, inserted into the pLEXSY-sat2 vector and transfected into L. tarentolae cells by electroporation. Culturing was carried out, and the secreted recombinant protein with a C-terminal histidine tag purified using nickel affinity chromatography on the culture supernatant, yielding a final product at 0.4 mg/mL. An indirect enzyme linked immunosorbent assay (ELISA) was standardised using sera from 74 Brazilian patients with cutaneous leishmaniasis and 11 with visceral leishmaniasis. Optimal ELISA conditions were established for the Lbk39 antigen in comparison with a crude extract from L. braziliensis. The sensitivity, specificity analysis and receiver operating characteristic (ROC) curve were determined with a significance level of 5%. The ROC curve showed a good accuracy with an area under curve (AUC) = 0.967, p < 0.001 (0.941-0.993) for CL patients and an AUC = 100 (100-100) for VL patients. The values of sensitivity and specificity were 88 and 98% for CL and 100 and 100% for VL, respectively. The study showed good production and expression of the target protein and has generated a potential new antigen for the diagnosis of leishmaniasis.

Multiplex flow cytometry serology to diagnosis of canine visceral leishmaniasis

An accurate diagnosis of visceral leishmaniasis is an essential tool for control of the disease. While serologic methods are very useful, these conventional methodologies still present limitations in terms of sensitivity and specificity. The use of flow cytometry is a worldwide trend in the development of high-performance diagnostic methods. Herein, we describe a new flow cytometry serology test, characterized by the employment of the Cytometric Bead Array microspheres A4 and E4 coated with the recombinant antigens rLci1A and rLci2B respectively, to improve the serodiagnosis of canine visceral leishmaniasis. The tests were conducted in a wide variety of sera groups (n = 140), where the diagnostics development would be optimized accounting not just the ability to identify infected dogs with different clinical status, but also to exclude cross-reaction and differentiate vaccinated dogs from dogs infected. Serological testing of the antigenic system A4-rLci1A showed a sensitivity of 90.0% and specificity of 75%, while the E4-rLci2B testing demonstrated a sensitivity of 95.0% and specificity of 82.5%. The use of a multiplex assay of A4-rLci1A and E4-rLci2B, resulted in a diagnostic improvement, with a sensitivity of 95.0% and specificity of 91.2%. Our results show that this novel flow cytometry serology test is a viable tool for sensitive and specific serodiagnosis. Notably, the combination of distinct antigenic systems allows us to test for antibodies to multiple recombinant antigens from a single serum sample. This benefit emphasizes the importance of this methodology as an alternative in the serological diagnosis.

Performance evaluation of anti-fixed Leishmania infantum promastigotes immunoglobulin G (IgG) detected by flow cytometry as a diagnostic tool for visceral Leishmaniasis

Visceral Leishmaniasis (VL) is a severe disease, caused by the protozoans Leishmania infantum and L. donovani that is widely diagnosed using serological tools. These, however, have limitations in performance that limit their use for the correct identification of the cases. This study aimed to evaluate the performance of flow cytometry with fixed parasites for VL diagnosis, comparing it with four other serological tests. Samples from two endemic VL regions in Brazil, diagnosed by direct examination (DG1) and by at least two or one standard serological test (DG2 and DG3, respectively), as well as patients with chronic Chagas' disease (CG1) and healthy controls (CG2) were used in this study. The flow cytometry results were expressed as levels of IgG reactivity, based on the percentage of positive fluorescent parasites (PPFP). Using a 1:4096 serum dilution, a ROC curve analysis of the serum titration on flow cytometry has indicated a PPFP of 2% as the cutoff point to segregate positive and negative results. In the present study, flow cytometry had the best performance for DG1 (sensitivity of 96%) while rK39 (imunocromagraphic rapid test) and DAT (Direct agglutination test) were also associated with high sensitivity and specificity. The substantial agreement and kappa indexes observed suggested similar performances between these two tests and flow cytometry. IFAT (Immunofluorescent antibody test) and ELISA (Enzyme-linked immunosorbent assay) had lower performances and the lower values of agreement with flow cytometry. Together, these findings suggest that although adjustments are needed in order to reduce cross reactivity with other trypanosomatids, flow cytometry has the potential to be a safe serological alternative for the diagnosis of VL.

High accuracy of an ELISA test based in a flagella antigen of Leishmania in serodiagnosis of canine visceral leishmaniasis with potential to improve the control measures in Brazil - A Phase II study

BACKGROUND

Canine Visceral leishmaniasis (CVL) is a serious public health problem, thus for its control, the Ministry of Health in Brazil recommends the rapid diagnosis and euthanasia of seropositive dogs in endemic areas. Therefore, our group had previously selected six recombinant proteins (rLci1, rLci2, rLci4, rLci5, rLci8, and rLci12) due to their high potential for CVL diagnostic testing. The present study aims to produce an immunodiagnostic test using the aforementioned antigens, to improve the performance of the diagnosis of CVL recommended by Brazilian Ministry of Health.

METHODOLOGY/PRINCIPAL FINDINGS

To evaluate the recombinant proteins in the serological assays, positive and negative samples were selected based on parasitological test (culture) and molecular test (qPCR) of splenic aspirate. Initially, we selected 135 dog serum samples, 73 positives (symptomatic and asymptomatic) and 62 negatives to screen recombinant proteins on ELISA platform. Then, for rLci5 ELISA validation, 361 serum samples collected in a cross-sectional study were selected, being 183 positives (symptomatic and asymptomatic) and 178 negatives. In the screening of the recombinant proteins, rLci5 was the only protein to present a performance statistically higher than the performance presented by EIE-LVC test, presenting 96% (IC 95%; 85-99%) vs. 83% (IC 95%; 69-92%) of sensitivity for symptomatic dogs, 71% (IC 95%; 49-97%) vs. 54% (IC 95%; 33-74%) for asymptomatic dogs and 94% (IC 95%; 83-99%) vs, 88% (IC 95%; 76-95% of specificity. Thus, the rLci5 protein was selected to compose a final ELISA test. Validation of rLci5 ELISA showed 87% (IC 81-91%) of sensitivity, 94% (IC 95%; 90-97%) of specificity and 90% accuracy. Testing the EIE-LVC with the same validation panel, we observed a lower performance when compared to ELISA rLci5 (sensitivity of 67% (IC 95%; 59-74%), specificity of 87% (IC 95%; 81-92%), and accuracy of 77%). Finally, the performance of current CVL diagnostic protocol recommended by Brazilian Ministry of Health, using DPP-LVC as screening test and EIE-LVC as confirmatory test, was compared with a modified protocol, replacing EIE-LVC by rLci5 ELISA. The current protocol presented a sensitivity of 59% (IC 95%; 52-66%), specificity of 98% (IC 95%; 95-99%) and accuracy of 80% (IC 95%; 76-84%), while the modified protocol presented a sensitivity of 71% (IC 95%; 63-77%), specificity of 99% (IC 95%; 97-100%) and accuracy of 86% (IC 95%; 83-89%).

CONCLUSION

Thus, we concluded that rLci5 ELISA is a promising test to replace EIE-LVC test and increase the diagnostic performance of CVL in Brazil.

Evaluation of a new set of recombinant antigens for the serological diagnosis of human and canine visceral leishmaniasis

Current strategies for the control of zoonotic visceral leishmaniasis (VL) rely on its efficient diagnosis in both human and canine hosts. The most promising and cost effective approach is based on serologic assays with recombinant proteins. However, no single antigen has been found so far which can be effectively used to detect the disease in both dogs and humans. In previous works, we identified Leishmania infantum antigens with potential for the serodiagnosis of VL. Here, we aimed to expand the panel of the available antigens for VL diagnosis through another screening of a genomic expression library. Seven different protein-coding gene fragments were identified, five of which encoding proteins which have not been previously studied in Leishmania and rich in repetitive motifs. Poly-histidine tagged polypeptides were generated from six genes and evaluated for their potential for diagnosis of VL by ELISA (Enzyme Linked ImmunoSorbent Assay) with sera from infected humans and dogs. None of those was valid for the detection of human VL (26–52% sensitivity) although their performance was increased in the canine sera (48–91% sensitivity), with one polypeptide useful for the diagnosis of canine leishmaniasis. Next, we assayed a mixture of three antigens, found to be best for human or canine VL, among 13 identified through different screenings. This “Mix” resulted in similar levels of sensitivity for both human (84%) and canine (88%) sera. With improvements, this validates the use of multiple proteins, including antigens identified here, as components of a single system for the diagnosis of both forms of leishmaniasis.

Synthetic Peptides as Potential Antigens for Cutaneous Leishmaniosis Diagnosis

This work's goal was to research new candidate antigens for cutaneous leishmaniosis (CL). In order to reach the goal, we used random peptide phage display libraries screened using antibodies from Leishmania braziliensis patients. After selection, three peptides (P1, P2, and P3) were synthesized using Fmoc chemistry. The peptides individually or a mixture of them (MIX) was subsequently emulsified in complete and incomplete Freund's adjuvant and injected subcutaneously in golden hamsters. Sera from the hamsters administered with P1 presented antibodies that recognized proteins between 76 and 150 kDa from L. braziliensis. Sera from hamsters which had peptides P2 and P3, as well as the MIX, administered presented antibodies that recognized proteins between 52 and 76 kDa of L. braziliensis. The research on the similarity of the peptides' sequences in protein databases showed that they match a 63 kDa glycoprotein. The three peptides and the MIX were recognized by the sera from CL patients by immunoassay approach (ELISA). The peptides' MIX showed the best performance (79% sensitivity) followed by the P1 (72% sensitivity), and the AS presented 91% sensitivity. These results show a new route for discovering molecules for diagnosis or for immunoprotection against leishmaniosis.

Proteins Selected in Leishmania (Viannia) braziliensis by an Immunoproteomic Approach with Potential Serodiagnosis Applications for Tegumentary Leishmaniasis

The serodiagnosis of human tegumentary leishmaniasis (TL) presents some problems, such as the low level of antileishmanial antibodies found in most of the patients, as well as the cross-reactivity in subjects infected by other trypanosomatids. In the present study, an immunoproteomic approach was performed aimed at identification of antigens in total extracts of stationary-phase promastigote and amastigote-like forms of Leishmania (Viannia) braziliensis using sera from TL patients. With the purpose of reducing the cross-reactivity of the identified proteins, spots recognized by sera from TL patients, as well as those recognized by antibodies present in sera from noninfected patients living in areas where TL is endemic and sera from Chagas disease patients, were discarded. Two Leishmania hypothetical proteins and 18 proteins with known functions were identified as antigenic. The study was extended with some of them to validate the results of the immunoscreening. The coding regions of five of the characterized antigens (enolase, tryparedoxin peroxidase, eukaryotic initiation factor 5a, β-tubulin, and one of the hypothetical proteins) were cloned in a prokaryotic expression vector, and the corresponding recombinant proteins were purified and evaluated for the serodiagnosis of TL. The antigens presented sensitivity and specificity values ranging from 95.4 to 100% and 82.5 to 100%, respectively. As a comparative antigen, a preparation of Leishmania extract showed sensitivity and specificity values of 65.1 and 57.5%, respectively. The present study has enabled the identification of proteins able to be employed for the serodiagnosis of TL.

Leishmaniases diagnosis: an update on the use of immunological and molecular tools

Leishmaniases are caused by obligate intracellular protozoan parasites of the genus Leishmania. They cause a spectrum of diseases, most notably visceral (VL), cutaneous (CL), and mucosal (ML) leishmaniasis, which affect millions of people around the world, each year. Despite scientific advances, leishmaniases cases are expanding, constituting an important public health problem. Immunological and molecular diagnostic tools have been increasingly applied for the early detection of these parasitic infections, since the existence of limitations in clinical and parasitological examinations may provide false results, thus interfering in epidemiological research and diseases control. Although there is a great diversity of available immunological assays, important common deficiencies persist, which explains the current exploration of the molecular biology in research fields, especially the Polymerase Chain Reaction (PCR) and its variants, such as real-time quantitative PCR. However, in the last years, significant results have also been reached inside of immunological context (especially by Flow Cytometry), for humans and dogs, demonstrated by research works of the New and Old worlds. In spite of their potential to clarify and minimize the present global situation of the diseases, the implementation of molecular or immunological innovative reference assays for VL and CL at health services is still a challenge due to several reasons, including lack of standardization among laboratories and structural concerns. In this article we bring classical and current information about technological advances for the immunological and molecular leishmaniases diagnosis, their features, and applications.

Multi-antigen print immunoassay (MAPIA)-based evaluation of novel recombinant Leishmania infantum antigens for the serodiagnosis of canine visceral leishmaniasis

Background

Domestic dogs are the principal reservoir hosts of Leishmania infantum in regions where visceral leishmaniasis (VL) is endemic. Although serologic methods are frequently used for the screening of infected dogs, antibody-based tests require further assessment, due to lack of sensitivity and specificity. In this study, we employed a multi-antigen printing immunoassay (MAPIA) to compare the antibody responses to novel recombinant proteins of L. infantum with the potential for the detection of canine VL.

Findings

MAPIA strips were prepared employing 12 recombinant proteins. Antibody reactivity to these antigens was compared using a panel of sera collected from clinically asymptomatic (n = 16) and symptomatic (n = 41) culture-positive animals. Our findings showed that the canine immune response to antigen differs between dogs and depends on infection status. Using this screening assay, when five out of the 12 antigens were combined, an overall 81% detection rate of L. infantum-infected dogs was achieved.

Conclusions

We conclude that MAPIA is an effective screening tool to rapidly select multiple antigens of diagnostic utility to be used in a more sensitive point of care diagnostic test such as the Dual-Path Platform (DPP) multiplex test for the rapid detection of infected dogs.

Novel recombinant multiepitope proteins for the diagnosis of asymptomatic leishmania infantum-infected dogs

Background

Visceral leishmaniasis is the most severe form of leishmaniasis. Worldwide, approximately 20% of zoonotic human visceral leishmaniasis is caused by Leishmania infantum, also known as Leishmania chagasi in Latin America. Current diagnostic methods are not accurate enough to identify Leishmania-infected animals and may compromise the effectiveness of disease control. Therefore, we aimed to produce and test two recombinant multiepitope proteins as a means to improve and increase accuracy in the diagnosis of canine visceral leishmaniasis (CVL).

Methodology/Principal Findings

Ten antigenic peptides were identified by CVL ELISA in previous work. In the current proposal, the coding sequences of these ten peptides were assembled into a synthetic gene. Furthermore, other twenty peptides were selected from work by our group where good B and T cell epitopes were mapped. The coding sequences of these peptides were also assembled into a synthetic gene. Both genes have been cloned and expressed in Escherichia coli, producing two multiepitope recombinant proteins, PQ10 and PQ20. These antigens have been used in CVL ELISA and were able to identify asymptomatic dogs (80%) more effectively than EIE-LVC kit, produced by Bio-Manguinhos (0%) and DPP kit (10%). Moreover, our recombinant proteins presented an early detection (before PCR) of infected dogs, with positivities ranging from 23% to 65%, depending on the phase of infection in which sera were acquired.

Conclusions/Significance

Our study shows that ELISA using the multiepitope proteins PQ10 and PQ20 has great potential in early CVL diagnosis. The use of these proteins in other methodologies, such as immunochromatographic tests, could be beneficial mainly for the detection of asymptomatic dogs.

Visceral leishmaniasis is the most severe form among leishmaniasis, being a neglected disease caused by a protozoan parasite. Its transmission through phlebotominae bites, between dogs and humans, classifies it as a zoonotic disease. It is caused by the specie Leishmania infantum ( = L. chagasi) and represents 20% of the world's human visceral leishmaniasis. Visceral leishmaniasis is a serious public health issue, fatal if untreated, and its incidence is increasing in urban areas of the tropics. In Brazil, one of the control measures is the identification and elimination of infected dogs, which act as reservoirs for Leishmania parasites. Diagnostic methods used to identify infection in these animals are still not accurate enough, which may compromise the effectiveness of this control measure. Thus, to contribute to the diagnosis of canine visceral leishmaniasis, we aimed to develop and test two new antigens that could be applied in early detection of infected dogs.

Evaluation of three recombinant Leishmania infantum antigens in human and canine visceral leishmaniasis diagnosis

Visceral leishmaniasis (VL) is a neglected disease and is fatal if untreated. Dogs serve as reservoirs for Leishmania infantum (syn. L. chagasi) due to their susceptibility to infection and high skin parasitism. Therefore, VL control in Brazil involves the elimination of seropositive dogs, among other actions. However, the most frequently used serological tests have limitations regarding sensitivity and specificity. In this study, we have selected three Leishmania antigens (C1, C8 and C9) and have produced them as recombinant proteins using pET-28a-TEV vector and Escherichia coli BL-21 as expression system. When tested in ELISA with human samples, the C9 antigen was the one showing the most promising results, with 68% sensitivity and 78% specificity. When testing canine samples, the C1, C8 and C9 antigens showed a sensitivity range from 70% to 80% and specificity range from 60% to 90%. The C1 antigen presented higher sensitivity (80%) and the C8 antigen presented higher specificity (90%). Due to it, we decided to mix and test C1 and C8 antigens together, resulting in the C18 antigen. The mix also yielded high percentages of detected symptomatic and asymptomatic dogs however it did not improve the performance of the diagnostic. Comparison of our tests with the tests recommended by the Brazilian Ministry of Health revealed that our antigens' sensitivities and the percentage of detected asymptomatic dogs were much higher. Our results suggest that the C1, C8, C18 and C9 recombinant proteins are good antigens to diagnose canine visceral leishmaniasis and could potentially be used in screening tests. To diagnose human visceral leishmaniasis, the C9 antigen presented reasonable results, but more optimization must be performed for this antigen to provide better performance.

A multicentric evaluation of the recombinant Leishmania infantum antigen-based immunochromatographic assay for the serodiagnosis of canine visceral leishmaniasis

Background

Visceral leishmaniasis (VL) is a serious public health challenge in Brazil and dogs are considered to be the main urban reservoir of the causative agent. The culling of animals to control VL in some countries makes the accurate diagnosis of canine VL (CVL) essential. Recombinant antigens rLci1A and rLci2B were selected from a cDNA library of Leishmania infantum amastigotes due to their strong potential as candidates in diagnostic testing for CVL. The present multicentric study aimed to evaluate the sensitivity of a prototype test using these antigens (DPP rLci1A/rLci2B) against 154 sera obtained from symptomatic dogs within three endemic areas of VL in Brazil. The specificity was evaluated using 40 serum samples from negative dogs and dogs infected with other pathogens. Sensitivity and specificity rates of DPP rLci1A/rLci2B prototype were compared to rates from other diagnostic tests currently in use by the Brazilian Ministry of Health, including DPP®LVC, EIE®LVC.

Findings

DPP rLci1A/rLci2B prototype offered similar performance to that offered by DPP®LVC rapid test, as follows: sensitivity of 87% (CI 81–91) and 88% (CI 82–93) and specificity of 100% (CI 91–100) and 97% (CI 87–100), respectively for DPP rLci1A/rLci2B and DPP®LVC. When results of these two tests were considered concomitantly, sensitivity increased to 93.5% (CI 89–96).

Conclusions

The recombinant antigens rLci1A and rLci2B represent promising candidates for use in a multi-antigen rapid test for CVL. The inclusion of novel antigens to the DPP rLci1A/rLci2B prototype model could offer additionally enhanced sensitivity to detect animals infected by L. infantum.