The risk factors for relapse among patients with African trypanosomiasis in Daloa, Cote d'Ivoire

We describe rates of follow-up and the risk factors for relapse in a cohort of adult patients treated for Trypanosoma brucei gambiense African trypanosomiasis. 812 patients were discharged from hospital between 6 January 1983 and 16 January 1992. The numbers who did not attend a scheduled follow-up appointment at 6,12,18 and 24 months were 383 (47%), 467 (58%), 536 (66%) and 533 (66%), respectively. Thirty-two patients relapsed over the 2 years follow-up: 24 (75%) before the 12-month follow-up appointment. The presence of antibody to trypanosomes in the cerebrospinal fluid (CSF) at discharge from hospital was associated significantly with the risk of relapse at any time. When the analysis was restricted to a follow-up of 1 year, a protein level in the CSF above the median and the presence of antibody in the CSF (both at discharge) were associated in univariate analysis with relapse. A high number of patients were lost to follow-up, which may have resulted in bias. From the data available, the majority of the relapses were recorded within 12 months and the presence of antibody in the CSF at hospital discharge was identified as an independent predictor of future relapse at any time.

Immunogenicity and Serological Cross-Reactivity of Saliva Proteins among Different Tsetse Species

Tsetse are vectors of pathogenic trypanosomes, agents of human and animal trypanosomiasis in Africa. Components of tsetse saliva (sialome) are introduced into the mammalian host bite site during the blood feeding process and are important for tsetse’s ability to feed efficiently, but can also influence disease transmission and serve as biomarkers for host exposure. We compared the sialome components from four tsetse species in two subgenera: subgenus Morsitans: Glossina morsitans morsitans (Gmm) and Glossina pallidipes (Gpd), and subgenus Palpalis: Glossina palpalis gambiensis (Gpg) and Glossina fuscipes fuscipes (Gff), and evaluated their immunogenicity and serological cross reactivity by an immunoblot approach utilizing antibodies from experimental mice challenged with uninfected flies. The protein and immune profiles of sialome components varied with fly species in the same subgenus displaying greater similarity and cross reactivity. Sera obtained from cattle from disease endemic areas of Africa displayed an immunogenicity profile reflective of tsetse species distribution. We analyzed the sialome fractions of Gmm by LC-MS/MS, and identified TAg5, Tsal1/Tsal2, and Sgp3 as major immunogenic proteins, and the 5'-nucleotidase family as well as four members of the Adenosine Deaminase Growth Factor (ADGF) family as the major non-immunogenic proteins. Within the ADGF family, we identified four closely related proteins (TSGF-1, TSGF-2, ADGF-3 and ADGF-4), all of which are expressed in tsetse salivary glands. We describe the tsetse species-specific expression profiles and genomic localization of these proteins. Using a passive-immunity approach, we evaluated the effects of rec-TSGF (TSGF-1 and TSGF-2) polyclonal antibodies on tsetse fitness parameters. Limited exposure of tsetse to mice with circulating anti-TSGF antibodies resulted in a slight detriment to their blood feeding ability as reflected by compromised digestion, lower weight gain and less total lipid reserves although these results were not statistically significant. Long-term exposure studies of tsetse flies to antibodies corresponding to the ADGF family of proteins are warranted to evaluate the role of this conserved family in fly biology.

Insect saliva contains many proteins that are injected into the mammalian host during the blood feeding process. Saliva proteins enhance the blood feeding ability of insects, but they can also induce mammalian immune responses that inhibit successful feeding, or modulate the bite site to benefit pathogen transmission. Here we studied saliva from four different tsetse species that belong to two distant species groups. We show that the saliva protein profiles of different species groups vary. Experimental mice subjected to fly bites display varying immunological responses against the abundant saliva proteins and the antigenicity of the shared saliva proteins in different tsetse species differs. We show that one member of the ADGF family with adenosine deaminase motifs, TSGF-2, is non-immunogenic in Glossina morsitans in mice, while the same protein from Glossina fuscipes is highly immunogenic. Such species-specific immune responses could be exploited as biomarkers of host exposures in the field. We also show that short-term exposure of G. morsitans to mice passively immunized by anti-TSGF antibodies leads to slight but not statistically significant negative fitness effects. Thus, future investigations with non-antigenic saliva proteins are warranted as they can lead to novel mammalian vaccine targets to reduce tsetse populations in the field.

Experimental African Trypanosome Infection by Needle Passage or Natural Tsetse Fly Challenge Thwarts the Development of Collagen-Induced Arthritis in DBA/1 Prone Mice via an Impairment of Antigen Specific B Cell Autoantibody Titers

Collagen-induced arthritis is a B cell-mediated autoimmune disease. Recently published studies have demonstrated that in some rare cases pathogens can confer protection from autoimmunity. Trypanosoma brucei parasites are tsetse fly transmitted extracellular protozoans causing sleeping sickness disease in humans and Nagana in livestock in sub-Saharan endemic areas. In the past, we demonstrated that trypanosome infections impair B cell homeostasis and abolish vaccine-induced protection against unrelated antigens. Hence, here we hypothesized that trypanosome infection can affect the onset of CIA by specifically dampening specific B-cell responses and type II collagen antibody titers in DBA/1 prone mice. We observed a substantial delay in the onset of collagen-induced arthritis in T. brucei-infected DBA/1 mice that correlates with a drastic decrease of type II collagen titers of the different IgG isotypes in the serum. Treatment of infected mice with Berenil, a trypanocidal drug, restored the development of CIA-associated clinical symptoms. Interestingly, these data were confirmed by the challenge of immunized DBA/1 prone mice with T. brucei-infected tsetse flies. Together, these results demonstrate that T. brucei infection is impairing the maintenance of the antigen specific plasma B cell pool driving the development of CIA in DBA/1 prone mice.

Evaluation of the diagnostic accuracy of prototype rapid tests for human African trypanosomiasis

Background

Diagnosis of human African trypanosomiasis (HAT) remains a challenge both for active screening, which is critical in control of the disease, and in the point-of-care scenario where early and accurate diagnosis is essential. Recently, the first field deployment of a lateral flow rapid diagnostic test (RDT) for HAT, “SD BIOLINE HAT” has taken place. In this study, we evaluated the performance of “SD BIOLINE HAT” and two new prototype RDTs.

Methodology/Principal Findings

The performance of “SD BIOLINE HAT” and 2 prototype RDTs was tested using archived plasma from 250 Trypanosoma brucei gambiense patients, and 250 endemic controls. As well as comparison of the sensitivity and specificity of each device, the performance of individual antigens was assessed and the hypothetical performance of novel antigen combinations extrapolated. Neither of the prototype devices were inferior in sensitivity or specificity to “SD BIOLINE HAT” (sensitivity 0.82±0.01, specificity 0.97±0.01, 95% CI) at the 5% margins, while one of the devices (BBI) had significantly superior sensitivity (0.88±0.03). Analysis of the performance of individual antigens was used to model new antigen combinations to be explored in development of the next generation of HAT RDTs. The modelling showed that an RDT using two recombinant antigens (rLiTat1.5 and rISG65) would give a performance similar to the best devices in this study, and would also offer the most robust performance under deteriorating field conditions.

Conclusions/Significance

Both “SD BIOLINE HAT” and the prototype devices performed comparably well to one another and also to the published performance range of the card agglutination test for trypanosomiasis in sensitivity and specificity. The performance of individual antigens enabled us to predict that an all-recombinant antigen RDT can be developed with an accuracy equivalent to “ SD BIOLINE HAT.” Such an RDT would have advantages in simplified manufacture, lower unit cost and assured reproducibility.

The most prevalent species of trypanosome causing human African trypanosomiasis (HAT), Trypanosoma brucei gambiense, presents a diagnostic challenge. While early diagnosis is essential for effective treatment and also to control transmission, symptoms are non-specific and parasitological diagnosis is laborious and technically difficult. Screening for HAT suspects has until now been done using the card agglutination test for trypanosomiasis (CATT), which requires a cold chain and equipment, making it difficult to deploy. Thus there is an urgent need for sensitive point of care diagnostic tests that are suitable for use in rural areas in terms of stability, simplicity and cost. We describe the evaluation of 3 rapid diagnostic tests (RDTs) for HAT based on lateral flow devices that detect antibodies against defined parasite antigens in blood samples. We demonstrate that the SD BIOLINE HAT RDT currently being deployed in HAT endemic regions, as well as two new prototype devices, are accurate in screening for HAT. By analysing the sensitivity of each of the antigens used in the devices tested, we predict that a highly sensitive RDT based on recombinant antigens can be developed. An all-recombinant antigen RDT offers significant benefits in manufacturing reproducibility and cost, and would dramatically simplify HAT diagnosis.

Unravelling human trypanotolerance: IL8 is associated with infection control whereas IL10 and TNFα are associated with subsequent disease development

In West Africa, Trypanosoma brucei gambiense, causing human African trypanosomiasis (HAT), is associated with a great diversity of infection outcomes. In addition to patients who can be diagnosed in the early hemolymphatic phase (stage 1) or meningoencephalitic phase (stage 2), a number of individuals can mount long-lasting specific serological responses while the results of microscopic investigations are negative (SERO TL+). Evidence is now increasing to indicate that these are asymptomatic subjects with low-grade parasitemia. The goal of our study was to investigate the type of immune response occurring in these “trypanotolerant” subjects. Cytokines levels were measured in healthy endemic controls (n = 40), stage 1 (n = 10), early stage 2 (n = 19), and late stage 2 patients (n = 23) and in a cohort of SERO TL+ individuals (n = 60) who were followed up for two years to assess the evolution of their parasitological and serological status. In contrast to HAT patients which T-cell responses appeared to be activated with increased levels of IL2, IL4, and IL10, SERO TL+ exhibited high levels of proinflammatory cytokines (IL6, IL8 and TNFα) and an almost absence of IL12p70. In SERO TL+, high levels of IL10 and low levels of TNFα were associated with an increased risk of developing HAT whereas high levels of IL8 predicted that serology would become negative. Further studies using high throughput technologies, hopefully will provide a more detailed view of the critical molecules or pathways underlying the trypanotolerant phenotype.

Whereas immunological mechanisms involved in the control of trypanosome infections have been extensively studied in animal models, knowledge of how Trypanosoma brucei gambiense interacts with its human hosts lags far behind. In this study we measured cytokine levels in sleeping sickness patients and individuals who were apparently able to control infection to subdetection levels over long periods of time or who were engaged in a process of self-cure as demonstrated by the disappearance of specific antibodies. In contrast to patients, trypanotolerant subjects were characterized by a strong inflammatory response with elevated levels of IL8, IL6, and TNFα. This study indicates that both protective immune responses and markers of disease development exist in human T. brucei. gambiense infection and constitute an important step forward to identify new diagnostic or therapeutic targets in the fight against sleeping sickness.

Recombinant antigens expressed in Pichia pastoris for the diagnosis of sleeping sickness caused by Trypanosoma brucei gambiense

BACKGROUND

Screening tests for gambiense sleeping sickness, such as the CATT/T. b. gambiense and a recently developed lateral flow tests, are hitherto based on native variant surface glycoproteins (VSGs), namely LiTat 1.3 and LiTat 1.5, purified from highly virulent trypanosome strains grown in rodents.

METHODOLOGY/PRINCIPAL FINDINGS

We have expressed SUMO (small ubiquitin-like modifier) fusion proteins of the immunogenic N-terminal part of these antigens in the yeast Pichia pastoris. The secreted recombinant proteins were affinity purified with yields up to 10 mg per liter cell culture.

CONCLUSIONS/SIGNIFICANCE

The diagnostic potential of each separate antigen and a mixture of both antigens was confirmed in ELISA on sera from 88 HAT patients and 74 endemic non-HAT controls. Replacement of native antigens in the screening tests for sleeping sickness by recombinant proteins will eliminate both the infection risk for the laboratory staff during antigen production and the need for laboratory animals. Upscaling production of recombinant antigens, e.g. in biofermentors, is straightforward thus leading to improved standardisation of antigen production and reduced production costs, which on their turn will increase the availability and affordability of the diagnostic tests needed for the elimination of gambiense HAT.

Cyclical appearance of African trypanosomes in the cerebrospinal fluid: new insights in how trypanosomes enter the CNS

It is textbook knowledge that human infective forms of Trypanosoma brucei, the causative agent of sleeping sickness, enter the brain across the blood-brain barrier after an initial phase of weeks (rhodesiense) or months (gambiense) in blood. Based on our results using an animal model, both statements seem questionable. As we and others have shown, the first infection relevant crossing of the blood brain border occurs via the choroid plexus, i.e. via the blood-CSF barrier. In addition, counting trypanosomes in blood-free CSF obtained by an atlanto-occipital access revealed a cyclical infection in CSF that was directly correlated to the trypanosome density in blood infection. We also obtained conclusive evidence of organ infiltration, since parasites were detected in tissues outside the blood vessels in heart, spleen, liver, eye, testis, epididymis, and especially between the cell layers of the pia mater including the Virchow-Robin space. Interestingly, in all organs except pia mater, heart and testis, trypanosomes showed either a more or less degraded appearance of cell integrity by loss of the surface coat (VSG), loss of the microtubular cytoskeleton and loss of the intracellular content, or where taken up by phagocytes and degraded intracellularly within lysosomes. This is also true for trypanosomes placed intrathecally into the brain parenchyma using a stereotactic device. We propose a different model of brain infection that is in accordance with our observations and with well-established facts about the development of sleeping sickness.

Gambiense human african trypanosomiasis and immunological memory: effect on phenotypic lymphocyte profiles and humoral immunity

In mice, experimental infection with Trypanosoma brucei causes decreased bone marrow B-cell development, abolished splenic B-cell maturation and loss of antibody mediated protection including vaccine induced memory responses. Nothing is known about this phenomenon in human African trypanosomiasis (HAT), but if occurring, it would imply the need of revaccination of HAT patients after therapy and abolish hope for a HAT vaccine. The effect of gambiense HAT on peripheral blood memory T- and B-cells and on innate and vaccine induced antibody levels was examined. The percentage of memory B- and T-cells was quantified in peripheral blood, prospectively collected in DR Congo from 117 Trypanosoma brucei gambiense infected HAT patients before and six months after treatment and 117 controls at the same time points. Antibodies against carbohydrate antigens on red blood cells and against measles were quantified. Before treatment, significantly higher percentages of memory B-cells, mainly T-independent memory B-cells, were observed in HAT patients compared to controls (CD20+CD27+IgM+, 13.0% versus 2.0%, p<0.001). The percentage of memory T-cells, mainly early effector/memory T-cells, was higher in HAT (CD3+CD45RO+CD27+, 19.4% versus 16.7%, p = 0.003). After treatment, the percentage of memory T-cells normalized, the percentage of memory B-cells did not. The median anti-red blood cell carbohydrate IgM level was one titer lower in HAT patients than in controls (p<0.004), and partially normalized after treatment. Anti-measles antibody concentrations were lower in HAT patients than in controls (medians of 1500 versus 2250 mIU/ml, p = 0.02), and remained so after treatment, but were above the cut-off level assumed to provide protection in 94.8% of HAT patients, before and after treatment (versus 98.3% of controls, p = 0.3). Although functionality of the B-cells was not verified, the results suggest that immunity was conserved in T.b. gambiense infected HAT patients and that B-cell dysfunction might not be that severe as in mouse models.

DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes

Antigenic variation in African trypanosomes requires monoallelic transcription and switching of variant surface glycoprotein (VSG) genes. The transcribed VSG, always flanked by ‘70 bp’-repeats and telomeric-repeats, is either replaced through DNA double-strand break (DSB) repair or transcriptionally inactivated. However, little is known about the subtelomeric DSBs that naturally trigger antigenic variation in Trypanosoma brucei, the subsequent DNA damage responses, or how these responses determine the mechanism of VSG switching. We found that DSBs naturally accumulate close to both transcribed and non-transcribed telomeres. We then induced high-efficiency meganuclease-mediated DSBs and monitored DSB-responses and DSB-survivors. By inducing breaks at distinct sites within both transcribed and silent VSG transcription units and assessing local DNA resection, histone modification, G₂/M-checkpoint activation, and both RAD51-dependent and independent repair, we reveal how breaks at different sites trigger distinct responses and, in ‘active-site’ survivors, different switching mechanisms. At the active site, we find that promoter-adjacent breaks typically failed to trigger switching, 70 bp-repeat-adjacent breaks almost always triggered switching through 70 bp-repeat recombination (∼60% RAD51-dependent), and telomere-repeat-adjacent breaks triggered switching through loss of the VSG expression site (25% of survivors). Expression site loss was associated with G₂/M-checkpoint bypass, while 70 bp-repeat-recombination was associated with DNA-resection, γH2A-focus assembly and a G₂/M-checkpoint. Thus, the probability and mechanism of antigenic switching are highly dependent upon the location of the break. We conclude that 70 bp-repeat-adjacent and telomere-repeat-adjacent breaks trigger distinct checkpoint responses and VSG switching pathways. Our results show how subtelomere fragility can generate the triggers for the major antigenic variation mechanisms in the African trypanosome.

Previous studies on antigenic variation in African trypanosomes relied upon positive or negative selection, yielding only cells that underwent variation. This made it difficult to define individual switched clones as independent, potentially introduced bias in the relative contribution of each switching mechanism and precluded analysis of cells undergoing switching. We show that DNA double-strand breaks (DSBs) naturally accumulate close to Trypanosoma brucei telomeres. Using the I-SceI meganuclease, we then established a system to trigger breaks in all cells in a population. The specificity, temporal constraint and efficiency of cleavage facilitated the application of a quantitative approach to dissecting subtelomeric break responses and their consequences. Accordingly, we show that the DSB-site determines probability and mechanism of antigenic switching, that DSBs can trigger switching via recombination or transcription inactivation and that a checkpoint-bypass mechanism can explain switching via VSG expression site deletion. Our results provide major new insights into the mechanisms underlying antigenic variation and provide a new model to explain how the repeats flanking VSG genes serve distinct roles in fragility and recombination. The findings are also relevant to telomeric gene rearrangements that control immune evasion in other protozoal, fungal and bacterial pathogens such as Plasmodium, Pneumocystis and Borrelia species, respectively.

Proteomic selection of immunodiagnostic antigens for human African trypanosomiasis and generation of a prototype lateral flow immunodiagnostic device

Background

The diagnosis of Human African Trypanosomiasis relies mainly on the Card Agglutination Test for Trypanosomiasis (CATT). While this test is successful, it is acknowledged that there may be room for improvement. Our aim was to develop a prototype lateral flow test based on the detection of antibodies to trypanosome antigens.

Methodology/Principal Findings

We took a non-biased approach to identify potential immunodiagnostic parasite protein antigens. The IgG fractions from the sera from Trypanosoma brucei gambiense infected and control patients were isolated using protein-G affinity chromatography and then immobilized on Sepharose beads. The IgG-beads were incubated with detergent lysates of trypanosomes and those proteins that bound were identified by mass spectrometry-based proteomic methods. This approach provided a list of twenty-four trypanosome proteins that selectively bound to the infection IgG fraction and that might, therefore, be considered as immunodiagnostic antigens. We selected four antigens from this list (ISG64, ISG65, ISG75 and GRESAG4) and performed protein expression trials in E. coli with twelve constructs. Seven soluble recombinant protein products (three for ISG64, two for ISG65 and one each for ISG75 and GRESAG4) were obtained and assessed for their immunodiagnostic potential by ELISA using individual and/or pooled patient sera. The ISG65 and ISG64 construct ELISAs performed well with respect to detecting T. b. gambiense infections, though less well for detecting T. b. rhodesiense infections, and the best performing ISG65 construct was used to develop a prototype lateral flow diagnostic device.

Conclusions/Significance

Using a panel of eighty randomized T. b. gambiense infection and control sera, the prototype showed reasonable sensitivity (88%) and specificity (93%) using visual readout in detecting T. b. gambiense infections. These results provide encouragement to further develop and optimize the lateral flow device for clinical use.

Human African Trypanosomiasis is caused by infection with Trypanosoma brucei gambiense or T. b. rhodesiense. Preliminary diagnosis of T. b. gambiense infection relies mainly on a Card Agglutination Test for Trypanosomiasis (CATT), which has acknowledged limitations. New approaches are needed, first to identify new diagnostic antigens and, second, to find a more suitable platform for field-based immunodiagnostic tests. We took an unbiased approach to identify candidate diagnostic antigens by asking which parasite proteins bind to the antibodies of infected patients and not to the antibodies of uninfected patients. From this list of twenty-four candidate antigens, we selected four and from these we selected the one that worked the best in conventional immunodiagnostic tests. This antigen, ISG65, was used to make lateral flow devices, where a small sample of patient serum is added to a pad and thirty minutes later infection can be inferred by simple optical read out. This simple prototype device works as well as the CATT test and may be developed and optimized for clinical use in the field.

Structure of the trypanosome haptoglobin-hemoglobin receptor and implications for nutrient uptake and innate immunity

African trypanosomes are protected by a densely packed surface monolayer of variant surface glycoprotein (VSG). A haptoglobin-hemoglobin receptor (HpHbR) within this VSG coat mediates heme acquisition. HpHbR is also exploited by the human host to mediate endocytosis of trypanolytic factor (TLF)1 from serum, contributing to innate immunity. Here, the crystal structure of HpHbR from Trypanosoma congolense has been solved, revealing an elongated three α-helical bundle with a small membrane distal head. To understand the receptor in the context of the VSG layer, the dimensions of Trypanosoma brucei HpHbR and VSG have been determined by small-angle X-ray scattering, revealing the receptor to be more elongated than VSG. It is, therefore, likely that the receptor protrudes above the VSG layer and unlikely that the VSG coat can prevent immunoglobulin binding to the receptor. The HpHb-binding site has been mapped by single-residue mutagenesis and surface plasmon resonance. This site is located where it is readily accessible above the VSG layer. A single HbHpR polymorphism unique to human infective T. brucei gambiense has been shown to be sufficient to reduce binding of both HpHb and TLF1, modulating ligand affinity in a delicate balancing act that allows nutrient acquisition but avoids TLF1 uptake.

Trypanosoma brucei gambiense group 1 is distinguished by a unique amino acid substitution in the HpHb receptor implicated in human serum resistance

Trypanosoma brucei rhodesiense (Tbr) and T. b. gambiense (Tbg), causative agents of Human African Trypanosomiasis (sleeping sickness) in Africa, have evolved alternative mechanisms of resisting the activity of trypanosome lytic factors (TLFs), components of innate immunity in human serum that protect against infection by other African trypanosomes. In Tbr, lytic activity is suppressed by the Tbr-specific serum-resistance associated (SRA) protein. The mechanism in Tbg is less well understood but has been hypothesized to involve altered activity and expression of haptoglobin haemoglobin receptor (HpHbR). HpHbR has been shown to facilitate internalization of TLF-1 in T.b. brucei (Tbb), a member of the T. brucei species complex that is susceptible to human serum. By evaluating the genetic variability of HpHbR in a comprehensive geographical and taxonomic context, we show that a single substitution that replaces leucine with serine at position 210 is conserved in the most widespread form of Tbg (Tbg group 1) and not found in related taxa, which are either human serum susceptible (Tbb) or known to resist lysis via an alternative mechanism (Tbr and Tbg group 2). We hypothesize that this single substitution contributes to reduced uptake of TLF and thus may play a key role in conferring serum resistance to Tbg group 1. In contrast, similarity in HpHbR sequence among isolates of Tbg group 2 and Tbb/Tbr provides further evidence that human serum resistance in Tbg group 2 is likely independent of HpHbR function.

Identification of mimotopes with diagnostic potential for Trypanosoma brucei gambiense variant surface glycoproteins using human antibody fractions

Background

At present, screening of the population at risk for gambiense human African trypanosomiasis (HAT) is based on detection of antibodies against native variant surface glycoproteins (VSGs) of Trypanosoma brucei (T.b.) gambiense. Drawbacks of these native VSGs include culture of infective T.b. gambiense trypanosomes in laboratory rodents, necessary for production, and the exposure of non-specific epitopes that may cause cross-reactions. We therefore aimed at identifying peptides that mimic epitopes, hence called “mimotopes,” specific to T.b. gambiense VSGs and that may replace the native proteins in antibody detection tests.

Methodology/Principal Findings

A Ph.D.-12 peptide phage display library was screened with polyclonal antibodies from patient sera, previously affinity purified on VSG LiTat 1.3 or LiTat 1.5. The peptide sequences were derived from the DNA sequence of the selected phages and synthesised as biotinylated peptides. Respectively, eighteen and twenty different mimotopes were identified for VSG LiTat 1.3 and LiTat 1.5, of which six and five were retained for assessment of their diagnostic performance. Based on alignment of the peptide sequences on the original protein sequence of VSG LiTat 1.3 and 1.5, three additional peptides were synthesised. We evaluated the diagnostic performance of the synthetic peptides in indirect ELISA with 102 sera from HAT patients and 102 endemic negative controls. All mimotopes had areas under the curve (AUCs) of ≥0.85, indicating their diagnostic potential. One peptide corresponding to the VSG LiTat 1.3 protein sequence also had an AUC of ≥0.85, while the peptide based on the sequence of VSG LiTat 1.5 had an AUC of only 0.79.

Conclusions/Significance

We delivered the proof of principle that mimotopes for T.b. gambiense VSGs, with diagnostic potential, can be selected by phage display using polyclonal human antibodies.

Control of the chronic form of sleeping sickness or gambiense human African trypanosomiasis (HAT) consists of accurate diagnosis followed by treatment. We aim to replace the native variant surface glycoprotein (VSG) parasite antigens that are presently used in most antibody detection tests with peptides that can be synthesised in vitro. Antibodies recognising VSG were purified from HAT patient sera and were used to select phage-expressed peptides that mimic VSG epitopes from a Ph.D.-12 phage display library. The diagnostic potential of the corresponding synthetic peptides was demonstrated in indirect ELISA with sera from HAT patients and endemic negative controls. We proved that diagnostic mimotopes for T.b. gambiense VSGs can be selected by phage display technology, using polyclonal human antibodies.

Accuracy of five algorithms to diagnose gambiense human African trypanosomiasis

Background

Algorithms to diagnose gambiense human African trypanosomiasis (HAT, sleeping sickness) are often complex due to the unsatisfactory sensitivity and/or specificity of available tests, and typically include a screening (serological), confirmation (parasitological) and staging component. There is insufficient evidence on the relative accuracy of these algorithms. This paper presents estimates of the accuracy of five algorithms used by past Médecins Sans Frontières programmes in the Republic of Congo, Southern Sudan and Uganda.

Methodology and Principal Findings

The sequence of tests in each algorithm was programmed into a probabilistic model, informed by distributions of the sensitivity, specificity and staging accuracy of each test, constructed based on a literature review. The accuracy of algorithms was estimated in a baseline scenario and in a worst-case scenario introducing various near worst-case assumptions. In the baseline scenario, sensitivity was estimated as 85–90% in all but one algorithm, with specificity above 99.9% except for the Republic of Congo, where CATT serology was used as independent confirmation test: here, positive predictive value (PPV) was estimated at <50% in realistic active screening prevalence scenarios. Furthermore, most algorithms misclassified about one third of true stage 1 cases as stage 2, and about 10% of true stage 2 cases as stage 1. In the worst-case scenario, sensitivity was 75–90% and PPV no more than 75% at 1% prevalence, with about half of stage 1 cases misclassified as stage 2.

Conclusions

Published evidence on the accuracy of widely used tests is scanty. Algorithms should carefully weigh the use of serology alone for confirmation, and could enhance sensitivity through serological suspect follow-up and repeat parasitology. Better evidence on the frequency of low-parasitaemia infections is needed. Simulation studies should guide the tailoring of algorithms to specific scenarios of HAT prevalence and availability of control tools.

Gambiense human African trypanosomiasis (HAT, sleeping sickness) usually features low prevalence. The two stages of the disease require different treatments, and stage 2 is fatal if untreated. HAT diagnosis must therefore be highly sensitive (i.e., detect as many true cases as possible) and specific (i.e., minimize false positives). HAT diagnostic algorithms are complex and involve several tests to screen for, confirm and stage infection. We analyzed five algorithms used by Médecins Sans Frontières HAT programmes. We combined published data on the accuracy of each test in the algorithm with a computer program that simulates all possible algorithm branches. We found that all algorithms had reasonable sensitivity (85–90%); specificity was high (>99.9%) except for the Republic of Congo, where confirmation did not rely on microscopic evidence, resulting in frequent false positives (but also higher sensitivity). Algorithms misclassified about one third of stage 1 cases as stage 2, but stage 2 classification was highly accurate. The use of serology alone for confirmation merits caution. HAT diagnosis could be made more sensitively by following up serological suspects and repeating microscopic examinations. Computer simulations can help to adapt algorithms to local conditions in each HAT programme, such as the prevalence of infection and operational constraints.

Identification of peptide mimotopes of Trypanosoma brucei gambiense variant surface glycoproteins

Background

The current antibody detection tests for the diagnosis of gambiense human African trypanosomiasis (HAT) are based on native variant surface glycoproteins (VSGs) of Trypanosoma brucei (T.b.) gambiense. These native VSGs are difficult to produce, and contain non-specific epitopes that may cause cross-reactions. We aimed to identify mimotopic peptides for epitopes of T.b. gambiense VSGs that, when produced synthetically, can replace the native proteins in antibody detection tests.

Methodology/Principal Findings

PhD.-12 and PhD.-C7C phage display peptide libraries were screened with mouse monoclonal antibodies against the predominant VSGs LiTat 1.3 and LiTat 1.5 of T.b. gambiense. Thirty seven different peptide sequences corresponding to a linear LiTat 1.5 VSG epitope and 17 sequences corresponding to a discontinuous LiTat 1.3 VSG epitope were identified. Seventeen of 22 synthetic peptides inhibited the binding of their homologous monoclonal to VSG LiTat 1.5 or LiTat 1.3. Binding of these monoclonal antibodies to respectively six and three synthetic mimotopic peptides of LiTat 1.5 and LiTat 1.3 was significantly inhibited by HAT sera (p<0.05).

Conclusions/Significance

We successfully identified peptides that mimic epitopes on the native trypanosomal VSGs LiTat 1.5 and LiTat 1.3. These mimotopes might have potential for the diagnosis of human African trypanosomiasis but require further evaluation and testing with a large panel of HAT positive and negative sera.

The control of human African trypanosomiasis or sleeping sickness, a deadly disease in sub-Saharan Africa, mainly depends on a correct diagnosis and treatment. The aim of our study was to identify mimotopic peptides (mimotopes) that may replace the native proteins in antibody detection tests for sleeping sickness and hereby improve the diagnostic sensitivity and specificity. We selected peptide expressing phages from the PhD.-12 and PhD.-C7C phage display libraries with mouse monoclonal antibodies specific to variant surface glycoprotein (VSG) LiTat 1.3 or LiTat 1.5 of Trypanosoma brucei gambiense. The peptide coding genes of the selected phages were sequenced and the corresponding peptides were synthesised. Several of the synthetic peptides were confirmed as mimotopes for VSG LiTat 1.3 or LiTat 1.5 since they were able to inhibit the binding of their homologous monoclonal to the corresponding VSG. These peptides were biotinylated and their diagnostic potential was assessed with human sera. We successfully demonstrated that human sleeping sickness sera recognise some of the mimotopes of VSG LiTat 1.3 and LiTat 1.5, indicating the diagnostic potential of such peptides.

[Molecular dialogue between African trypanosomes and humans]

The evolutionary origin of Man in the African continent has imposed the requirement to resist endemic parasites, in particular African trypanosomes (prototype: Trypanosoma brucei). Therefore, human serum is provided with an efficient system of innate immunity against these parasites, as discovered by A. Laveran in 1902. However, two T. brucei clones, termed T. b. rhodesiense and T. b. gambiense, managed to escape this immunity system, enabling them to grow in humans where they cause sleeping sickness. We have identified the gene allowing T. b. rhodesiense to resist trypanolysis by human serum, which led us to discover that the trypanolytic factor is apolipoprotein L1 (apoL1). ApoL1 is a human-specific serum protein bound to HDL particles that also contain another human-specific protein termed "haptoglobin-related protein " (Hpr). Following the binding of hemoglobin (Hb) to Hpr, the apoL1-bearing HDL particles are avidly taken up by the trypanosome through their binding to a parasite surface receptor for the Hp-Hb complex. After endocytosis apoL1 kills the parasite by generating anionic pores in the lysosomal membrane. In our laboratory, mutant versions of apoL1 have been constructed, which are no longer neutralized by the resistance protein of T. b. rhodesiense and are therefore able to kill this human pathogen. Unexpectedly, we have recently discovered that similar mutants do actually exist in nature : in Africans and Americans of recent African origin, even a single allele of these mutants allows protection against infection by T. b. rhodesiense, but the price to pay is a high frequency of end-stage renal disease when doubly allelic. The evidence of natural selection of these apoL1 mutations despite their deleterious potential for kidneys highlights the importance of the resistance to trypanosomes in the evolution of Man. The mechanism by which mutant apoL1 triggers end-stage renal disease is currently studied.

The human trypanolytic factor: a drug shaped naturally

African trypanosomes are responsible for sleeping sickness in man and nagana in cattle, which are both tremendous health burdens in Africa. Most African trypanosome species are killed by human serum. This is due to a serum trypanolytic particle specific of some old world monkeys and great apes, an HDL subclass containing two proteins which appeared recently in mammalian evolution, apolipoprotein L1 and haptoglobin related protein. Nevertheless, two African trypanosome species, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense are able to infect humans, because they developed resistance to trypanolysis. Resistance to human serum in Trypanosoma brucei rhodesiense is due to a single gene called SRA. This mechanism of lysis-resistance is therefore an example of a natural drug-antidote system which evolved during a pathogen-host arms race. The lysis and resistance mechanisms, their molecular components as well as their mode of action are reviewed. I also discuss how components of the system would be suitable drug targets and how the system could be engineered to generate an effective synthetic drug.

Human African trypanosomiasis

Human African trypanosomiasis (sleeping sickness) occurs in sub-Saharan Africa. It is caused by the protozoan parasite Trypanosoma brucei, transmitted by tsetse flies. Almost all cases are due to Trypanosoma brucei gambiense, which is indigenous to west and central Africa. Prevalence is strongly dependent on control measures, which are often neglected during periods of political instability, thus leading to resurgence. With fewer than 12 000 cases of this disabling and fatal disease reported per year, trypanosomiasis belongs to the most neglected tropical diseases. The clinical presentation is complex, and diagnosis and treatment difficult. The available drugs are old, complicated to administer, and can cause severe adverse reactions. New diagnostic methods and safe and effective drugs are urgently needed. Vector control, to reduce the number of flies in existing foci, needs to be organised on a pan-African basis. WHO has stated that if national control programmes, international organisations, research institutes, and philanthropic partners engage in concerted action, elimination of this disease might even be possible.

[African trypanosomiasis in the Republic of Guinea]

The information on the Gambian form of African human trypanosomiasis (AHT), collected in Guinea, is analyzed. The fauna of tsetse flies currently numbers at least 8 species. Two species are the vectors of AHT. These include G.(N.) palpalis and G.(N.) tachinoides, the latter of which is the vector of animal trypanosomiasis ("nagana" cattle disease) as well. In the period of 1991 to 1997, the country's incidence of AHT was 9.6:100,000. The highest morbidity was established in the natural region of Lower Guinea (23.4:100,000, with mortality rates of 1.1 to 18.5%). A clinical study of the population of a few villages in this region revealed 6 patients with AHT. Its clinical diagnosis was parasitologically verified. Preliminary studies suggest the circulation of the pathogen of AHT in Guinea, the most active foci of which are in Lower Guinea. The epidemiological features of AHT and its epidemic significance for Guinea are yet to be studied.

Treatment failure related to intrathecal immunoglobulin M (IgM) synthesis, cerebrospinal fluid IgM, and interleukin-10 in patients with hemolymphatic-stage sleeping sickness

Human African trypanosomiasis treatment is stage dependent, but the tests used for staging are controversial. Central nervous system involvement and its relationship with suramin treatment failure were assessed in 60 patients with parasitologically confirmed hemolymphatic-stage Trypanosoma brucei gambiense infection (white blood cell count of or=1.9 mg/liter (OR, 11.7; 95% CI, 2.7 to 50), a CSF end titer by the LATEX/IgM assay of >or=2 (OR, 10.4; 95% CI, 2.5 to 44), and a CSF interleukin-10 concentration of >10 pg/ml (OR, 5; 95% CI, 1.3 to 20). The sensitivities of these markers for treatment failure ranged from 43 to 79%, and the specificities ranged from 74 to 93%. The results show that T. brucei gambiense-infected patients who have signs of neuroinflammation in CSF and who are treated with drugs recommended for use at the hemolymphatic stage are at risk of treatment failure. This highlights the need for the development and the evaluation of accurate point-of-care tests for the staging of human African trypanosomiasis.

Seasonal variation in human African trypanosomiasis in Tarangire National Park in Babati district, Tanzania

A survey was carried out to determine seasonal epidemiological variation of human African trypanosomiasis (HAT) in Tarangire National Park and villages around it in Babati District, Tanzania. Concentration and Field's stain techniques were employed to examine the presence of trypanosomes in human blood samples. Tsetse flies were collected using traps and dissected under light microscope to examine for presence of trypanosomes. Retrospective data on HAT were sought from health facilities. Blood samples were collected from a total 509 individuals (306 during the dry and 203 during wet seasons). None of the individuals was infected with trypanosomes in the area. A total of 766 tsetse flies were collected. Of these, Glossina swynnertoni accounted for 94.6% and G. pallidipes for 5.4% of the total collection. The largest proportion (63.8%) of the tsetse flies was collected during the wet season. Glossina swynnertoni was most abundant tsetse species during both wet and dry seasons. Salivary gland examination revealed the presence of Trypanosoma brucei type of infection in 3.2% of tsetse flies collected. All infective trypanosomes were found during the dry season. This study concludes that the transmission and prevalence of HAT among human population in Tarangire National Pars and its surrounding villages is low despite the recent reports on tourists acquiring the infection during their visits to the Park. However, disease surveillance needs to be strengthened to monitor any impending epidemic.

Human/vector relationships during human African trypanosomiasis: initial screening of immunogenic salivary proteins of Glossina species

The morbidity and mortality of vector-borne diseases is closely linked to exposure of the human host to vectors. Qualitative and quantitative evaluation of individual exposure to arthropod bites by investigation of the specific immune response to vector saliva would make it possible to monitor individuals at risk of vectorial transmission of pathogens. The objective of this study was to evaluate and compare the antibody (IgG) response to saliva from uninfected Glossina species, vectors, or non-vectors of Trypanosoma brucei gambiense by detecting immunogenic proteins in humans residing in an area endemic for human African trypanosomiasis in the Democratic Republic of Congo. Our results suggest that the immunogenic profiles observed seemed specific to the Glossina species (vector or non-vector species) and to the infectious status of exposed individuals (infected or not infected). This preliminary work tends to support the feasibility of development of an epidemiologic tool based on this antibody response to salivary proteins.

Identification of a tryptophan-like epitope borne by the variable surface glycoprotein (VSG) of African trypanosomes

Antibodies (Ab) directed against a tryptophan-like epitope (WE) were previously detected in patients with human African trypanosomiasis (HAT). We investigated whether or not these Ab resulted from immunization against trypanosome antigen(s) expressing a WE. By Western blotting, we identified an antigen having an apparent molecular weight ranging from 60 to 65 kDa, recognized by purified rabbit anti-WE Ab. This antigen, present in trypomastigote forms, was absent in procyclic forms and Trypanosoma cruzi trypomastigotes. Using purified variable surface glycoproteins (VSG) from various trypanosomes, we showed that VSG was the parasite antigen recognized by these rabbit Ab. Anti-WE and anti-VSG Ab were purified from HAT sera by affinity chromatography. Immunoreactivity of purified antibodies eluted from affinity columns and of depleted fractions showed that WE was one of the epitopes borne by VSG. These data underline the existence of an invariant WE in the structure of VSG from several species of African trypanosomes.

The trypanolytic factor of human serum

African trypanosomes (the prototype of which is Trypanosoma brucei brucei) are protozoan parasites that infect a wide range of mammals. Human blood, unlike the blood of other mammals, has efficient trypanolytic activity, and this needs to be counteracted by these parasites. Resistance to this activity has arisen in two subspecies of Trypanosoma brucei - Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense - allowing these parasites to infect humans, and this results in sleeping sickness in East Africa and West Africa, respectively. Study of the mechanism by which T. b. rhodesiense escapes lysis by human serum led to the identification of an ionic-pore-forming apolipoprotein - known as apolipoprotein L1 - that is associated with high-density-lipoprotein particles in human blood. In this Opinion article, we argue that apolipoprotein L1 is the factor that is responsible for the trypanolytic activity of human serum.

Detection of trypanosome-specific antibodies in saliva, towards non-invasive serological diagnosis of sleeping sickness

OBJECTIVE

The detection of trypanosome-specific antibodies in saliva is technically feasible, and, if clinically validated, could become an attractive option for non-invasive diagnosis of sleeping sickness. We wanted to optimize the test format of an enzyme-linked immunosorbent assay (ELISA)-based antibody detection system.

METHODS

Different ELISA formats for antibody detection in serum and saliva were developed and standardized. Saliva and serum samples were collected from 78 patient and 128 endemic control samples, and sensitivity and specificity of saliva ELISAs, serum ELISAs and the card agglutination test for trypanosomiasis (CATT), were evaluated.

RESULTS

All ELISA formats showed sensitivity and specificity above 90%. Saliva ELISAs showed a similar test performance as serum ELISAs and the CATT on whole blood or serum.

CONCLUSIONS

This study confirms the potential of trypanosome-specific antibody detection in saliva.

Comparison of cytokine plasma levels in human African trypanosomiasis

BACKGROUND

Immunological studies suggest that human African trypanosomiasis (HAT) is associated with inflammatory responses. A better understanding of the complex cytokine interactions regulating HAT infections is essential to elucidate the mechanisms of generalized immunosuppression.

METHOD

We determined levels of interleukin (IL)-2, IL-4, IL-6, IL-10, tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma protein levels in plasma samples from three groups of individuals from the Democratic Republic of Congo: (i) HAT cases; (ii) seropositive individuals for whom parasite detection was negative and (ii) controls.

RESULTS

Plasma levels of six cytokines were significantly higher in HAT cases than in both controls (P<0.003) and seropositive individuals (P<0.016). IL-2 and IL-10 concentrations were significantly lower (P<0.02) in the seropositive group than in the control one.

CONCLUSION

Human African trypanosomiasis leads to the development of strong cytokine responses, indicating the potential involvement of IL-2 and IL-10 in the phenomenon of seropositivity without parasitological confirmation. This strongly suggests the involvement of immunity in this particular aspect of HAT epidemiology.

Dot enzyme-linked immunosorbent assay for more reliable staging of patients with Human African trypanosomiasis

Human African trypanosomiasis (HAT) or sleeping sickness is a disease characterized by a hemolymphatic stage 1 followed by a meningoencephalitic stage 2 which is fatal without specific treatment. Furthermore, due to the toxicity of drugs used to treat stage 2 (mainly melarsoprol) accurate staging is required. Actual criteria employed during field surveys are not sensitive enough for precise staging. Antineurofilament (anti-NF) and antigalactocerebrosides (anti-GalC) antibodies have been identified in cerebrospinal fluid (CSF) as potential markers of central nervous system (CNS) involvement. We describe a dot enzyme-linked immunosorbent assay (dot-ELISA) to detect anti-GalC and anti-NF antibodies and its value in staging. NF- and GalC-dotted nitrocellulose strips were first developed in our laboratory. They were then evaluated in Angola and Central African Republic on 140 CSF samples. Compared to our staging criteria (i.e., CSF cell count > or = 20 cells/microl, CSF immunoglobulin M concentration > or = 100 mg/liter, and/or the presence of trypanosomes in the CSF), combined detection of both CSF anti-NF and CSF anti-GalC by dot-ELISA showed 83.2% sensitivity and 100.0% specificity. Dot-ELISA could be a useful test to diagnose CNS involvement in HAT in the less-equipped laboratories or in the field situation and to improve patient treatment.

Options for field diagnosis of human african trypanosomiasis

Human African trypanosomiasis (HAT) due to Trypanosoma brucei gambiense or T. b. rhodesiense remains highly prevalent in several rural areas of sub-Saharan Africa and is lethal if left untreated. Therefore, accurate tools are absolutely required for field diagnosis. For T. b. gambiense HAT, highly sensitive tests are available for serological screening but the sensitivity of parasitological confirmatory tests remains insufficient and needs to be improved. Screening for T. b. rhodesiense infection still relies on clinical features in the absence of serological tests available for field use. Ongoing research is opening perspectives for a new generation of field diagnostics. Also essential for both forms of HAT is accurate determination of the disease stage because of the high toxicity of melarsoprol, the drug most widely used during the neurological stage of the illness. Recent studies have confirmed the high accuracy of raised immunoglobulin M levels in the cerebrospinal fluid for the staging of T. b. gambiense HAT, and a promising simple assay (LATEX/IgM) is being tested in the field. Apart from the urgent need for better tools for the field diagnosis of this neglected disease, improved access to diagnosis and treatment for the population at risk remains the greatest challenge for the coming years.

Neuro-inflammatory risk factors for treatment failure in “early second stage” sleeping sickness patients treated with Pentamidine

In a clinical trial on efficacy of Pentamidine in second stage Trypanosoma brucei gambiense patients with </=20 cells/microl in cerebrospinal fluid (CSF), 43% of treatment failures were observed. We hypothesised that unsuccessful treatment was caused by uncured brain infection. The relationship between treatment outcome and CSF cell count, protein concentration, presence of trypanosomes, the intrathecal immune response, and CSF total IgM and trypanosome specific antibodies detected by LATEX/IgM and LATEX/T.b. gambiense card agglutination tests was examined. Cell counts of 11-20 cells/microl, intrathecal IgM synthesis, CSF end-titres in LATEX/IgM >/=4 and LATEX/T.b. gambiense positive CSF, were associated with treatment failure. Detection of intrathecal IgM synthesis is valuable for assessment of brain involvement and treatment decision.

Circulating antibodies directed against nitrosylated antigens in trypanosome-infected mice

Nitric oxide has been implicated as an effector cytotoxic molecule in trypanosomiasis. In this work, we investigated the presence of circulating antibodies directed against nitrosylated epitopes as biological indicators for nitric oxide (NO) production in the sera of trypanosome-infected mice. We tested these sera with synthetic antigens, such as S-nitrosated protein or nitrosylated conjugates of amino acids that possess a high affinity to NO, by an immunoenzymatic assay. We detected antibodies directed against nitroso epitopes in the sera of infected mice, as compared to non-infected control mice. The antibody response was linked to the IgM isotype. Our results indicate the production of NO and its derivatives in trypanosomiasis. This production may potentially induce the synthesis of nitroso epitopes in vivo and favor the development of a humoral immune response.

Human African trypanosomiasis: quantitative and qualitative assessment of intrathecal immune response

Quantitative and qualitative techniques for assessment of the intrathecal humoral immune response in human African trypanosomiasis were compared, and their diagnostic potential for detection of the meningo-encephalitic stage of the disease was evaluated. Total and trypanosome specific immunoglobulin G (IgG) and IgM intrathecal synthesis were studied in paired cerebrospinal fluid (CSF) and blood samples of 38 trypanosomiasis patients and in three controls using Reiber's formulae. The presence of CSF-specific oligoclonal IgG and of trypanosome-specific antibodies was determined using iso-electric focusing followed by immunoblotting and antigen-driven immunoblots. The intrathecal IgG fraction (16% positive) and oligoclonal IgG detection (24% positive) were insensitive for detection of an intrathecal humoral immune response. Trypanosome-specific IgG synthesis, reflected by the IgG antibody index (AI) (26% positive), was confirmed by the presence of oligoclonal specific IgG (47% positive), but the latter was more sensitive. Although the detection technique failed for oligoclonal IgM, the intrathecal IgM fraction (42% positive) and the IgM AI (32% positive) indicated that the meningo-encephalitic stage of the disease is characterized by a dominant intrathecal IgM response, which was higher than the IgG response. The highest combination of diagnostic sensitivity and specificity for the meningo-encephalitic stage of trypanosomiasis was observed for quantitative IgM determinations.

Glycosylinositolphosphate soluble variant surface glycoprotein inhibits IFN-gamma-induced nitric oxide production via reduction in STAT1 phosphorylation in African trypanosomiasis

Macrophages are centrally involved in the host immune response to infection with Trypanosoma brucei rhodesiense, a protozoan parasite responsible for human sleeping sickness in Africa. During trypanosome infections, the host is exposed to parasite-derived molecules that mediate macrophage activation, specifically GPI anchor substituents associated with the shed variant surface glycoprotein (VSG), plus the host-activating agent IFN-gamma, which is derived from activated T cells and is essential for resistance to trypanosomes. In this study, we demonstrate that the level and timing of exposure of macrophages to IFN-gamma vs GPI ultimately determine the macrophage response at the level of induced gene expression. Treatment of macrophages with IFN-gamma followed by GIP-sVSG (the soluble form of VSG containing the glycosylinositolphosphate substituent that is released by parasites) stimulated the induction of gene expression, including transcription of TNF-alpha, IL-6, GM-CSF, and IL-12p40. In contrast, treatment of macrophages with GIP-sVSG before IFN-gamma stimulation resulted in a marked reduction of IFN-gamma-induced responses, including transcription of inducible NO synthase and secretion of NO. Additional experiments revealed that the inhibitory activity of GIP-sVSG was associated with reduction in the level of STAT1 phosphorylation, an event required for IFN-gamma-induced macrophage activation. These results suggest that modulation of specific aspects of the IFN-gamma response may be one mechanism by which trypanosomes overcome host resistance during African trypanosomiasis.

Towards saliva-based screening for sleeping sickness?

A pilot study was carried out on the detection of trypanosome-specific antibodies in saliva for diagnosis of sleeping sickness. All twenty-three saliva samples of parasitologically confirmed Trypanosoma brucei gambiense patients tested positive in an indirect enzyme-linked immunosorbent assay, whereas all 14 saliva samples of a negative control group remained negative. Trypanosome-specific antibody levels in patient saliva correlated with antibody levels in serum, but were about 250-fold lower. Eight of 23 undiluted saliva samples of sleeping sickness patients tested positive in CATT/T. b. gambiense and two of 23 in LATEX/T. b. gambiense. All fourteen saliva samples of the negative control group were also positive in CATT/T. b. gambiense, as were four of 14 in LATEX/T. b. gambiense. CATT and LATEX were thus inappropriate for antibody detection in saliva. These results indicate that trypanosome-specific antibody detection in saliva is possible. This could lead to the development of a simple, non-invasive, reliable saliva field test for diagnosis of sleeping sickness.

Stage determination and therapeutic decision in human African trypanosomiasis: value of polymerase chain reaction and immunoglobulin M quantification on the cerebrospinal fluid of sleeping sickness patients in Côte d'Ivoire

In human African trypanosomiasis (HAT), two disease stages are defined: the first, or haemo-lymphatic stage, and the second, or meningo-encephalitic stage. Stage determination forms the basis of therapeutic decision and is of prime importance, as the drug used to cure second-stage patients has considerable side-effects. However, the tests currently used for stage determination have low sensitivity or specificity. Two new tests for stage determination in the cerebrospinal fluid (CSF) were evaluated on 73 patients diagnosed with HAT in Côte d'Ivoire. The polymerase chain reaction (PCR) detecting trypanosome DNA (PCR/CSF) is an indirect test for trypanosome detection whereas the latex agglutination test detecting immunoglobulin M (LATEX/IgM) is an indicator for neuro-inflammation. Both tests were compared with classically used tests, double centrifugation and white blood cell count of the CSF. PCR/CSF appeared to be the most sensitive test (96%), and may be of use to improve stage determination. However, its value for therapeutic decision appears limited, as patients whose CSF was positive with PCR were successfully treated with pentamidine. This result confirms those of previous works that showed that some patients with trypanosomes in the CSF could be treated successfully with pentamidine. LATEX/IgM, which depending on the cut-off, showed lower sensitivity of 76% and 88%, but higher specificity of 83% and 71% for LATEX/IgM 16 and LATEX/IgM 8 respectively, appears more appropriate for therapeutic decision making.

Intrathecal immune response pattern for improved diagnosis of central nervous system involvement in trypanosomiasis

Diagnosis of central nervous system (CNS) involvement in human African trypanosomiasis is crucial in determination of therapy. Cerebrospinal fluid (CSF) and serum immunoglobulin concentrations, blood-CSF barrier dysfunction, pattern of intrathecal immunoglobulin synthesis, trypanosome-specific antibody synthesis, and CSF lactate concentrations were analyzed in 272 patients with Trypanosoma brucei gambiense infection. As part of the 2- or 3-class immune response, the predominant intrathecal IgM synthesis was the most sensitive (95%) marker for inflammation of the brain. We propose to replace the World Health Organization (WHO) criteria (white blood cell count >5 cells/microL and presence of trypanosomes in CSF) with a new approach for stage determination in trypanosomiasis: CNS involvement is diagnosed only in patients with >20 cells/microL or with intrathecal IgM synthesis, independent of the presence of trypanosomes in CSF. Compared with the use of these new criteria, the WHO criteria incorrectly classified 49 of 234 patients in the meningoencephalitic stage and 7 of 38 patients in the hemolymphatic disease stage. We also show that trypanosomiasis-related immunoglobulin patterns are of value in differential diagnosis.

Evaluation of LATEX/T.b.gambiense for mass screening of Trypanosoma brucei gambiense sleeping sickness in Central Africa

We compared the Card Agglutination Test for Trypanosomiasis (CATT), which consists of lyophilized bloodstream form trypomastigotes of Trypanosoma brucei gambiense (T.b.g.) variable antigen type LiTat 1.3, with LATEX/T.b.g., which consists of a lyophilized suspension of latex particles coated with variable surface glycoproteins of T.b.g. variable antigen types LiTat 1.3, 1.5 and 1.6. This study was carried out during two mass screening surveys in 1998 in Campo, a sleeping sickness focus in Cameroon, with a low prevalence (0.3%) and in 1999 in Batangafo which belongs to the Central African focus of Ouham which has a higher prevalence (3%). In Campo, we compared the CATT performed on whole blood with the LATEX/T.b.g. on diluted blood. In Batangafo, both tests were performed on diluted blood. In all circumstances, the specificity of the LATEX/T.b.g. was higher than of CATT. The use of LATEX/T.b.g. on diluted blood instead of CATT results in an important decrease of workload and as a consequence, of costs related to parasitological examinations. In the case of Campo the workload was up to 12 times less than when using CATT 1.3 on whole blood and the cost divided by 3. In Batangafo the workload was decreased by nearly 20% with the LATEX/T.b.g. Finally, it should be noted that in Batangafo, one of the parasitologically confirmed sleeping sickness patients was negative in CATT and positive in LATEX/T.b.g. and that the reading of the test result in LATEX/T.b.g. is easier than in CATT.

[Diagnosis of sleeping sickness stage: towards a new approach]

Diagnosis of the neurological disease stage in Trypanosoma brucei (T.b.) gambiense infection is essential to select an optimal chemotherapy. The actual parameters for stage determination, the cerebrospinal fluid (CSF) cell count, total protein concentration and trypanosome detection, are insufficiently specific and sensitive. In order to identify new parameters for stage determination, we studied the neuro-inflammatory immune response in the central nervous system, notably the intrathecal humoral immune response in sleeping sickness patients. The presence of intrathecal IgM synthesis was identified as an excellent marker of central nervous system involvement. However, intrathecal IgM detection cannot be performed under field conditions. As a consequence of the strong intrathecal IgM synthesis, extremely high concentrations of IgM are found in the CSF of sleeping sickness. We therefore developed a latex agglutination field test (LATEX/IgM) indicative for intrathecal IgM synthesis and CNS involvement in sleeping sickness. Based on our observations on the intrathecal immune response and with LATEX/IgM, we propose a new approach for stage determination in sleeping sickness.

[Human African trypanosomiasis in Ivory Coast: biological characteristics after treatment. 812 cases treated in the Daloa focus (Ivory Coast)]

The treatment and post therapeutic follow up of patients diagnosed with HAT are important for HAT control. A longitudinal survey was implemented in the focus of Daloa (Côte d'Ivoire). A total of 812 patients infected with Trypanosoma brucei gambiense in meningoencephalitic stage and treated with melarsoprol were included, this study pointed out the biological characteristics of patients after treatment. The relapse occurs between 1 and 24 months after treatment. It is essentially neurological, and characterised by the presence in the CSF of antibodies, by the increase of cell count compared with value immediately after treatment, or by the presence of trypanosomes. The cure can be confirmed from 18 months after treatment, and is characterised by the absence of antibodies and trypanosomes in the CSF, by a normal cell count and a normal proteinorachy. Biological scares were recorded on some of the patients after 18 months of follow up, but no relapse occurred among them.

Field evaluation of the CATT/Trypanosoma brucei gambiense on blood-impregnated filter papers for diagnosis of human African trypanosomiasis in southern Sudan

Most Human African Trypanosomiasis (HAT) control programmes in areas endemic for Trypanosoma brucei gambiense rely on a strategy of active mass screening with the Card Agglutination Test for Trypanosomiasis (CATT)/T. b. gambiense. We evaluated the performance, stability and reproducibility of the CATT/T. b. gambiense on blood-impregnated filter papers (CATT-FP) in Kajo-Keji County, South-Sudan, where some areas are inaccessible to mobile teams. The CATT-FP was performed with a group of 100 people with a positive CATT on whole blood including 17 confirmed HAT patients and the results were compared with the CATT on plasma (CATT-P). The CATT-FP was repeated on impregnated filter papers stored at ambient and refrigerated temperature for 1, 3, 7 and 14 days. Another 82 patients with HAT, including 78 with a positive parasitology, were tested with the CATT-FP and duplicate filter paper samples were sent to a reference laboratory to assess reproducibility. The CATT-FP was positive in 90 of 99 patients with HAT (sensitivity: 91%). It was less sensitive than the CATT-P (mean dilution difference: -2.5). There was no significant loss of sensitivity after storage for up to 14 days both at ambient and cool temperature. Reproducibility of the CATT-FP was found to be excellent (kappa: 0.84). The CATT-FP can therefore be recommended as a screening test for HAT in areas where the use of CATT-P is not possible. Further studies on larger population samples in different endemic foci are still needed before the CATT-FP can be recommended for universal use.

IgM quantification in the cerebrospinal fluid of sleeping sickness patients by a latex card agglutination test

An increased IgM concentration in cerebrospinal fluid (CSF), occurring as a consequence of massive intrathecal IgM synthesis, is a marker of interest for diagnosis of the meningo-encephalitic stage in human African trypanosomiasis. However, in current practice, IgM in CSF is not determined because of the lack of a simple and robust test that is applicable in African rural regions where the disease prevails. We describe the development of a sensitive semiquantitative card agglutination test, LATEX/IgM, for IgM quantification in CSF. The test is simple and fast and the lyophilized reagent remains stable even at 45 degrees C. CSF end-titres obtained with LATEX/IgM parallel the IgM concentrations determined by nephelometry and enzyme-linked immunosorbent assay. Detection of intrathecal IgM synthesis is the most sensitive marker for CNS involvement in sleeping sickness. At a cut-off value of >or= 8, the sensitivity and specificity of LATEX/IgM for intrathecal IgM synthesis are 89.4 and 92.7%. As a consequence, patients with LATEX/IgM end-titres >or= 8 are likely to have intrathecal IgM synthesis, thus central nervous system involvement and therefore should be treated accordingly. Further studies should concentrate on the relationship between the LATEX/IgM end-titres, presence of intrathecal IgM synthesis and occurrence of treatment failures in patients treated with pentamidine.

VSG-GPI anchors of African trypanosomes: their role in macrophage activation and induction of infection-associated immunopathology

African trypanosomes express a glycosylphosphatidyl inositol (GPI)-anchored variant-specific surface glycoprotein (VSG) as a protective coat. During infection, large amounts of VSG molecules are released into the circulation. Their interaction with various cells of the immune system underlies the severe infection-associated pathology. Recent results have shown that anti-GPI vaccination can prevent the occurrence of this pathology.

Stage determination and follow-up in sleeping sickness

In order to select a correct treatment after primary diagnosis of trypanosomiasis infection, accurate assessment of the disease stage, haemo-lymphatic or meningo-encephalitic, is essential. This is achieved by lumbar puncture and subsequent examination of the cerebrospinal fluid. These examinations have to be repeated during 2 years after treatment, and only after the cerebrospinal fluid has normalized one can decide on complete cure. The currently used cerebrospinal fluid parameters, i.e. white blood cell count, total protein determination and finding of trypanosomes, and practical problems encountered using these parameters are discussed. Alternative markers for stage determination and follow-up include trypanosome specific antibodies, anti-galactocerebroside antibodies and IgM measurement in CSF.

[Diagnosis of human African trypanosomiasis in 2001]

Human African trypanosomiasis is characterized by a non-specific clinical presentation with no consistent, pathognomonic manifestations. However definite diagnosis is necessary to avoid unnecessary therapeutic risks with toxic drugs. Further complicating this situation is the frequent need to achieve field diagnosis in remote locations with limited facilities. Serological tests such as CATT (card agglutination trypanosomiasis test) are useful for initial population screening to identify suspects but are not sufficiently reliable for definitive diagnosis since the variations in sensitivity and specificity have been observed between countries and disease pockets. Parasitological examination is still the only method of definitive diagnosis. Thresholds of trypanosome detection differ from one technique to another, i.e., 10,000 trypanosomes per millilitre (T/ml) for fresh blood smears, 5,000 T/ml for thick drop specimens stained with Giemsa, 500 T/ml for centrifugation in capillary tubes, less than 500 T/ml for the QBC test, and 100 T/ml for the ion exchange minicolumn system. The possibility that the QBC test and minicolumn anion exchange system may go out of production could pose a serious problem for field diagnosis. Decisional algorithms are being developed to optimize use of remaining techniques.

Blood-cerebrospinal fluid barrier and intrathecal immunoglobulins compared to field diagnosis of central nervous system involvement in sleeping sickness

Diagnosis of central nervous system (CNS) involvement in sleeping sickness is crucial in order to give an appropriate treatment regimen. Neurological symptoms occur late, therefore field diagnosis is based on white blood cell count, total protein concentration and presence of trypanosomes in cerebrospinal fluid (CSF). More sensitive and specific parameters are now available. Blood-CSF barrier (B-CSFB) dysfunction, intrathecal total and specific immunoglobulin synthesis were evaluated in 95 patients with and without obvious meningoencephalitis, and compared to field criteria.B-CSFB dysfunction is a rather late event in the course of CNS involvement and correlates with the presence of trypanosomes, neurological signs and intrathecal polyspecific and specific immune response. IgM intrathecal response and particularly IgM antibody index are early markers of CNS invasion. We showed that 29% of patients with CSF abnormalities but without trypanosome detection in the field had no neuro-immunological response. In contrast, patients with normal CSF according to field diagnosis showed an intrathecal immune response in 31% of the cases.Field diagnosis can therefore fail to determine neurological involvement but can also provide false positive results. Improved criteria including B-CSFB dysfunction and IgM detection are needed in order to provide an adapted treatment regimen.

Evaluation of an EDTA version of CATT/Trypanosoma brucei gambiense for serological screening of human blood samples

CATT/Trypanosoma brucei gambiense, a direct card agglutination test designed for field surveys on human African trypanosomosis, is currently used with freshly collected heparinized blood samples. When testing serum samples, it has been observed earlier that, at lower sample dilutions, a complement-mediated inhibition phenomenon may cause false negative test results. This can be avoided by adding an anticomplementary agent such as di-sodium ethylenediaminetetraacetate dihydrate (EDTA) to the reaction. As the sensitivity of the blood assay might be improved in the same way, this possibility has been examined under both laboratory and field conditions, by adding EDTA to the test buffer or, as an anticoagulant, to the blood samples. The CATT-EDTA versions proved up to 7% more sensitive but also 1-2% less specific than the current test. CATT buffer supplemented with EDTA remained stable for at least 2 years at +45 degrees C.

Evaluation of the micro-CATT, CATT/Trypanosoma brucei gambiense, and LATEX/T b gambiense methods for serodiagnosis and surveillance of human African trypanosomiasis in West and Central Africa

OBJECTIVE

To evaluate the performance of serological tests using dried blood on filter-papers (micro-card agglutination test for trypanosomiasis (micro-CATT)) performed under field and laboratory conditions and using whole blood ((CATT/T.b. gambiense) (wb-CATT) and latex agglutination (LATEX/T.b. gambiense) (wb-LATEX)) for the serodiagnosis and surveillance of human African trypanosomiasis in West and Central Africa.

METHODS

We evaluated the micro-CATT, wb-CATT and wb-LATEX methods in Côte d'Ivoire and the Central African Republic by screening 940 people. Sensitivity and specificity were calculated for each serological test; only patients with the confirmed presence of trypanosomes in the blood or lymph aspirate were considered true positives. Positive and negative predictive values were also calculated.

FINDINGS

Each of the tests showed a lower sensitivity in the Central African Republic than in Côte d'Ivoire.

CONCLUSION

The results confirmed the efficiency of the classic wb-CATT to detect sleeping sickness patients. The micro-CATT method can be used for human African trypanosomiasis surveillance if the test is performed on the same day as the blood collection, or if samples are stored at 4 degrees C. Otherwise, micro-CATT can be used when absolute sensitivity is not required. wb-LATEX should only be used for high-specificity screening.

Increased trypanolytic activity in sera of sleeping sickness patients after chemotherapy

We tested sera from patients previously treated for human African trypanosomiasis, from patients infected with trypanosomes, and from individuals never diagnosed with African trypanosomiasis living in the Trypanosoma brucei gambiense sleeping sickness focus of Mbini in Equatorial Guinea for their trypanolytic activity against bloodstream forms of T. b. rhodesiense expressing a metacyclic and bloodstream variant surface glycoprotein (VSG). Nearly 80% of the sera from treated patients showed high trypanolytic activity against trypanosomes expressing a metacyclic VSG. The trypanolytic activity of part of these sera was mediated by IgM while that of the other part was antibody-independent. On the other hand, only 40% of the sera exhibited high trypanolytic activity against trypanosomes expressing a bloodstream VSG which also was almost completely abolished by heat-inactivation. In contrast, most sera from infected and negative individuals displayed only low to moderate trypanolytic activity against either trypanosomes expressing a metacyclic or a bloodstream VSG. These results suggest that trypanolytic activity of sera increases after African sleeping sickness and is directed against trypanosomes expressing metacyclic VSG.

Human macrophage tumor necrosis factor (TNF)-alpha production induced by Trypanosoma brucei gambiense and the role of TNF-alpha in parasite control

Trypanosoma brucei gambiense, a causative agent of sleeping sickness, induced a dose-dependent production of tumor necrosis factor (TNF)-alpha by human macrophages in vitro. TNF-alpha was also induced in the Mono Mac 6 cell line, which indicates a direct effect of parasite components on macrophages. Parasite-soluble factors were also potent inducers of TNF-alpha. The addition of anti-TNF-alpha to cocultures of macrophages and parasites increased the number of trypanosomes and their life span, whereas irrelevant antibodies had no effect. TNF-alpha may have a direct role (i.e., direct trypanolytic activity) and/or an indirect one, such as TNF-alpha-mediated induction of cytotoxic molecules. A direct dose-dependent lytic effect of TNF-alpha on purified parasites was observed. This lytic effect was inhibited by anti-TNF-alpha. These data suggest that, as in experimental trypanosomiasis, TNF-alpha is involved in parasite growth control in human African trypanosomiasis.

A receptor-like flagellar pocket glycoprotein specific to Trypanosoma brucei gambiense

Trypanosoma brucei gambiense and T. b. rhodesiense are protozoan parasites causing sleeping sickness in humans due to their resistance to lysis by normal human serum (NHS). Based on the observation that the resistance gene of T. b. rhodesiense encodes a truncated form of the variant specific glycoprotein (VSG), we cloned a similar gene in T. b. gambiense using reverse transcription-linked polymerase chain reaction with VSG-specific primers. This gene, termed TgsGP for T. gambiense-specific glycoprotein, was found to be specific to T. b. gambiense. It is located close to a telomere and is transcribed by a pol II RNA polymerase, only at the bloodstream stage of the parasite development. TgsGP encodes a 47-kDa protein consisting of a N-terminal VSG domain presumably provided with a glycosylphosphatidylinositol (GPI) anchor sequence, similar to the pESAG6 subunit of the trypanosomal transferrin receptor. TgsGP is located in the flagellar pocket, and contains the linear N-linked polyacetyllactosamine characteristic of the endocytotic machinery of T. brucei. These observations strongly suggest that TgsGP is a T. b. gambiense specific receptor. Since stable expression of this protein in T. b. brucei did not confer resistance to NHS, TgsGP may either need another factor to achieve this purpose or fulfils another function linked to adaptation of the parasite to man.