Immunodiagnosis of canine visceral leishmaniasis using mimotope peptides selected from phage displayed combinatorial libraries

Synthetic Peptides Selected by Immunoinformatics as Potential Tools for the Specific Diagnosis of Canine Visceral Leishmaniasis

Diagnosing canine visceral leishmaniasis (CVL) in Brazil faces challenges due to the limitations regarding the sensitivity and specificity of the current diagnostic protocol. Therefore, it is urgent to map new antigens or enhance the existing ones for future diagnostic techniques. Immunoinformatic tools are promising in the identification of new potential epitopes or antigen candidates. In this study, we evaluated peptides selected by epitope prediction for CVL serodiagnosis in ELISA assays. Ten B-cell epitopes were immunogenic in silico, but two peptides (peptides No. 45 and No. 48) showed the best performance in vitro. The selected peptides, both individually and in combination, were highly diagnostically accurate, with sensitivities ranging from 86.4% to 100% and with a specificity of approximately 90%. We observed that the combination of peptides showed better performance when compared to peptide alone, by detecting all asymptomatic dogs, showing lower cross-reactivity in sera from dogs with other canine infections, and did not detect vaccinated animals. Moreover, our data indicate the potential use of immunoinformatic tools associated with ELISA assays for the selection and evaluation of potential new targets, such as peptides, applied to the diagnosis of CVL.

Mapping linear B-cell epitopes of the Tryparedoxin Peroxidase and its implications in the serological diagnosis of tegumentary leishmaniasis

Diagnosis of tegumentary leishmaniasis (TL) is essential to avoid permanent damage and severe functional sequelae and there is an urgent need to discover new antigens. The present study aimed to comprehensively evaluate the potential use of the Tryparedoxin Peroxidase (TryP) as an antigen for serological tests. The proposal integrates data from immunoproteomics with immunoinformatics, in addition to a precise analysis of protein levels in the evolutionary stages of the parasite by flow cytometry. To evaluate the performance in the diagnosis of TL, Enzyme-Linked Immunosorbent Assay (ELISA) assays were performed using the recombinant protein and the respective B-cell epitope, followed by an analysis of the contribution of this peptide in the recognition of the protein by patients, evaluated by serum depletion assays. We showed that the TryP has a linear B-cell epitope with high divergence compared to orthologs from Trypanosoma cruzi and Homo sapiens. The results also show high expression and positive cells for TryP (TryP⁺) in the infective metacyclic promastigotes (MET) and intracellular (24 and 48 hours) stages. From the depletion assays, it was possible to confirm the contribution of the peptide in the specific recognition of the TryP protein by patients with TL (13.7-15.9%). ELISA using the peptide showed high performance in the diagnosis compared to the recombinant TryP (rTryP), Soluble Leishmania braziliensis Antigen (sLba) and Immunofluorescence Assay (IFA) with accuracy of 94.29, 89.29, 65.00 and 37.14%, respectively). We can conclude that the MNEPAPP peptide is a potential antigen for the diagnosis of TL.

Diagnostic application of sensitive and specific phage-exposed epitopes for visceral leishmaniasis and human immunodeficiency virus coinfection

The diagnosis of visceral leishmaniasis (VL) has improved with the search of novel antigens; however, their performance is limited when samples from VL/human immunodeficiency virus (HIV)-coinfected patients are tested. In this context, studies conducted to identify more suitable antigens to detect both VL and VL/HIC coinfection cases should be performed. In the current study, phage display was performed using serum samples from healthy subjects and VL, HIV-infected and VL/HIV-coinfected patients; aiming to identify novel phage-exposed epitopes to be evaluated with this diagnostic purpose. Nine non-repetitive and valid sequences were identified, synthetized and tested as peptides in enzyme-linked immunosorbent assay experiments. Results showed that three (Pep2, Pep3 and Pep4) peptides showed excellent performance to diagnose VL and VL/HIV coinfection, with 100% sensitivity and specificity values. The other peptides showed sensitivity varying from 50.9 to 80.0%, as well as specificity ranging from 60.0 to 95.6%. Pep2, Pep3 and Pep4 also showed a potential prognostic effect, since specific serological reactivity was significantly decreased after patient treatment. Bioinformatics assays indicated that Leishmania trypanothione reductase protein was predicted to contain these three conformational epitopes. In conclusion, data suggest that Pep2, Pep3 and Pep4 could be tested for the diagnosis of VL and VL/HIV coinfection.

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.

Prevalence of Trypanosoma cruzi infection in active military population of The Colombian National Army gathered in five departments

Background

The National Army of Colombia is present in all of the national territory, focused in sylvatic zones where they are exposed continually to potential risk of transmission of Trypanosoma cruzi, the etiological agent of the Chagas disease. People of this study were active personal that were born and lived during their first years in endemic areas of transmission through domiciled vectors as Rhodnius prolixus.

Aim

The main aim of this study was to estimate the prevalence of Chagas disease in the active military population of the National Army, gathered in five departments.

Methods

An observational and descriptive study with cross-sectional analysis was carried out. Blood sample each patient in order to apply serological diagnosis by two different Enzyme Linked ImmunoSorbent Assay tests, following the algorithm of National Institute of Health, Colombia. In cases of serum results with inconsistencies, a Hemagglutination Inhibition test and Indirect Immunofluorescence assay test were performed to solve inconclusiveness. Positive samples by two different tests were considered seropositive. Additionally, to each positive sample by at least one serological test, we did extraction of DNA for molecular diagnosis.

Results

295 serums were analyzed and two of them were positive in order to get a prevalence of 0.68%. Two samples analyzed by molecular diagnosis were negative.

Conclusion

The prevalence was < 1% It is probable the infection in the seropositive individuals occurred before enlisting in the military service due to origin locations with transmission such as Casanare and Boyacá. These findings allow defining the prevention and control programs of chronic cases and reduction in the disease burden.

Diagnostic markers selected by immunoproteomics and phage display applied for the serodiagnosis of canine leishmaniosis

Canine leishmaniosis (CanL) is one of the most important parasitic diseases found in several countries worldwide. Dogs are considered important domestic reservoirs of the parasites, being relevant in the maintenance of transmission cycle of the disease between sandflies and humans. However, the prevalence of asymptomatic infection is considerably higher than that of apparent clinical illness in the infected animals; thus making promptly necessary to diagnose the infection in these animals, which could help to allow to the adoption of more efficient control measures against disease. Parasitological tests, which are considered as gold standard to demonstrate the infection and diagnose the disease, present problems related with their sensitivity. Also, the sample´s collect is considered invasive. As consequence, serological tests could be applied as an additional tool to detect the asymptomatic and symptomatic CanL. For this purpose, distinct recombinant antigens have been studied; however, problems in their sensitivity and/or specificity have been still registered. The present review focus in advances in the identification of new diagnostic targets applied for the CanL diagnose, represented here by recombinant single, combined or chimeric proteins, as well as by peptides that mimic epitopes (mimotopes); which were selected by means of immunoproteomics and phage display.

New antigens for the serological diagnosis of human visceral leishmaniasis identified by immunogenomic screening

Visceral leishmaniasis (VL) still represents a serious public health problem in Brazil due to the inefficiency of the control measures currently employed, that included early diagnosis and treatment of human cases, vector control, euthanasia of infected dogs and, recently approved in Brazil, treatment with Milteforam drug. Effective clinical management depend largely on early and unequivocal diagnosis, however, cross-reactivity have also been described in serological tests, especially when it refers to individuals from areas where Chagas' disease is also present. Thus, to discover new antigens to improve the current serological tests for VL diagnosis is urgently needed. Here, we performed an immunogenomic screen strategy to identify conserved linear B-cell epitopes in the predicted L. infantum proteome using the following criteria: i) proteins expressed in the stages found in the vertebrate host, amastigote stage, and secreted/excreted, to guarantee greater exposure to the immune system; ii) divergent from proteins present in other infectious disease pathogens with incidence in endemic areas for VL, as T. cruzi; iii) highly antigenic to humans with different genetic backgrounds, independently of the clinical stage of the disease; iv) stable and adaptable to quality-control tests to guarantee reproducibility; v) using statistical analysis to determine a suitable sample size to evaluate accuracy of diagnostic tests established by receiver operating characteristic strategy. We selected six predicted linear B-cell epitopes from three proteins of L. infantum parasite. The results demonstrated that a mixture of peptides (Mix IV: peptides 3+6) were able to identify VL cases and simultaneously able to discriminate infections caused by T. cruzi parasite with high accuracy (100.00%) and perfect agreement (Kappa index = 1.000) with direct methods performed by laboratories in Brazil. The results also demonstrated that peptide-6, Mix III (peptides 2+6) and I (peptides 2+3+6) are potential antigens able to used in VL diagnosis, represented by high accuracy (Ac = 99.52%, 99.52% and 98.56%, respectively). This study represents an interesting strategy for discovery new antigens applied to serologic diagnosis which will contribute to the improvement of the diagnosis of VL and, consequently, may help in the prevention, control and treatment of the disease in endemic areas of Brazil.

Epitope mapping of recombinant Leishmania donovani virulence factor A2 (recLdVFA2) and canine leishmaniasis diagnosis using a derived synthetic bi-epitope

Background

Leishmaniasis is one of the most important zoonotic diseases spread in Latin America. Since many species are involved in dog infection with different clinical manifestations, the development of specific diagnostic tests is mandatory for more accurate disease control and vaccine strategies.

Methodology/Principal findings

Seventy-five 15-mer peptides covering the sequence of recombinant Leishmania donovani virulence factor A2 (recLdVFA2) protein were prepared by Spot synthesis. Membrane-bound peptides immunoreactivity with sera from dogs immunized with recLdVFA2 and with a specific anti-recLdVFA2 monoclonal antibody allowed mapping of continuous B-cell epitopes. Five epitopes corresponding to the N-terminal region of recLdVFA2 (MKIRSVRPLVVLLVC, RSVRPLVVLLVCVAA, RPLVVLLVCVAAVLA, VVLLVCVAAVLALSA and LVCVAAVLALSASAE, region 1–28) and one located within the repetitive units (PLSVGPQAVGLSVG, regions 67–81 and 122–135) were identified. A 34-mer recLdVFA2-derived bi-epitope containing the sequence MKIRSVRPLVVLLVC linked to PLSVGPQAVGLSVG by a Gly-Gly spacer was chemically synthesized in its soluble form. The synthetic bi-epitope was used as antigen to coat ELISA plates and assayed with dog sera for in vitro diagnosis of canine visceral leishmaniasis (CVL). The assay proved to be highly sensitive (98%) and specific (99%).

Conclusions/Significance

Our work suggests that synthetic peptide-based ELISA strategy may be useful for the development of a sensitive and highly specific serodiagnosis for CVL or other parasitic diseases.

Leishmaniasis is a neglected tropical disease being among the six endemic prioritized diseases in the world. Visceral leishmaniasis (VL) is caused by Leishmania infantum and represents a serious public health problem in Brazil. Dogs are the main source of infection in the urban area and, in Brazil, the main strategies of the Visceral Leishmaniasis Control Program are directed to control the canine reservoir (serological survey and euthanasia of dogs which present reactive serum). In general, diagnosis of canine visceral leishmaniasis (CVL) has been presented as a problem for Brazilian public health services. The issue should be attributed mainly to the following factors: 1- range of similar clinical signs observed in other infectious diseases that affect dogs; 2- large percentage of asymptomatic or oligosymptomatic dogs; 3- nonspecific histopathological changes; 4- nonexistence of a diagnostic test 100% specific and sensitive. In this work, we developed a synthetic bi-epitope peptide as an antigen for immunodiagnostic ELISA to detect CVL. The biepitope used for ELISA assay accurately distinguish (98% sensitivity and 99% specificity) CVL dogs sera from non-infected dogs sera.

Evaluation of recombinant K39 antigen and various promastigote antigens in sero-diagnosis of visceral leishmaniasis in Bangladesh

Background

Definitive diagnosis of visceral leishmaniasis (VL) by demonstrating parasites in tissue smears or by culture involves invasive procedures, technical expertise and adequate laboratory facilities. Endemic countries rely mainly on serological tests to diagnose VL. Currently, the immunochromatographic test incorporating the recombinant K39 antigen (rK39 ICT) is the reference test for rapid diagnosis of VL in the Indian subcontinent. The performance of serological tests using rK39 and other promastigote antigens can vary due to differences in antigen expression, the various hosts and environmental factors. To achieve elimination of VL, diagnostic accuracy will be necessary for active case detection especially in those who carry asymptomatic infections. We evaluated the performance of rK39 ICT, enzyme linked immunosorbent assay using mixed Leishmania promastigotes from different Leishmania species (p-ELISA) and indirect fluorescent antibody test (IFAT) utilizing whole promastigotes from the Leishmania donovani complex for sero-diagnosis of VL in Bangladesh.

Methods

The sensitivity of each serological test was evaluated on 155 patients who were diagnosed to have VL by microscopy and/or by culture methods. Test specificities were calculated on 706 healthy blood donors, 91 diagnostic sera from patients with a febrile illness and sera from patients positive for malaria (n = 91) and Chagas disease (n = 91). All statistical calculations were at 95% confidence intervals.

Results

The sensitivities of rK39 ICT, p-ELISA and IFAT were 100%, 86.5% and 92.3%, respectively. All three serological methods had a pooled sensitivity of 82.6%. The specificities of rK39 ICT, p-ELISA and IFAT from combined control groups were 100%, 93.1% and 99.9%, respectively. The respective positive and negative predictive values of the tests were both 100% for rK39 ICT, 66.3% and 97.8% for p-ELISA and 99.3% and 98.8% for IFAT. The p-ELISA showed cross reactivity with 36.3% of sera positive for malaria and 28.6% of sera positive for Chagas disease while rK39 ICT and IFAT showed no cross reactivity.

Conclusion

This study confirms the efficiency of rK39 ICT for rapid diagnosis of VL. The p-ELISA using mixed promastigote antigens did not perform well as a serological test for VL in Bangladesh. Due to high sensitivity and specificity of whole promastigote antigen of L. donovani complex utilized in IFAT, this test can be considered in combination with rK39 ICT to confirm VL diagnosis when clinical diagnosis cannot distinguish between other diseases.