Proteomic Identification of Immunodiagnostic Antigens for Trypanosoma vivax Infections in Cattle and Generation of a Proof-of-Concept Lateral Flow Test Diagnostic Device

Improved serodiagnosis of Trypanosoma vivax infections in cattle reveals high infection rates in the livestock regions of Argentina

Bovine trypanosomosis, caused by Trypanosoma vivax, currently affects cattle and has a significant economic impact in sub-Saharan Africa and South America. The development of new diagnostic antigens is essential to improve and refine existing methods. Our study evaluated the efficacy of two recombinant antigens in detecting specific antibodies in cattle. These antigens are derivatives of an invariant surface glycoprotein (ISG) from T. vivax. A fraction of a previously described antigen (TvY486_0045500), designated TvISGAf, from an African strain was evaluated, and a new ISG antigen from an American isolate, TvISGAm, was identified. The two antigens were expressed as fusion proteins in Escherichia coli: TvISGAf was fused to the MBP-His-tag, and TvISGAm was obtained as a His-tag fused protein. An ELISA evaluation was conducted using these antigens on 149 positive and 63 negative bovine samples. The diagnostic performance was enhanced by the use of a combination of both antigens (referred to as TvISG-based ELISA), achieving a sensitivity of 89.6% and specificity of 93.8%. Following the validation of the TvISG-based ELISA, the seroprevalence of T. vivax infection in 892 field samples from cattle in the central region of Argentina was determined. The mean seroprevalence of T. vivax was 53%, with variation ranging from 21% to 69% among the six departments studied. These results support the use of the TvISG ELISA as a valuable serological tool for the detection and monitoring of T. vivax infection in cattle. Furthermore, we report for the first time the seroprevalence of T. vivax in Argentina, which highlights the widespread endemic nature of the disease in the region. In order to effectively manage the increasing spread of T. vivax in the vast livestock production areas of South America, it is essential to implement consistent surveillance programs and to adopt preventive strategies.

Vivaxin genes encode highly immunogenic, non-variant antigens on the Trypanosoma vivax cell-surface

Trypanosoma vivax is a unicellular hemoparasite, and a principal cause of animal African trypanosomiasis (AAT), a vector-borne and potentially fatal livestock disease across sub-Saharan Africa. Previously, we identified diverse T. vivax-specific genes that were predicted to encode cell surface proteins. Here, we examine the immune responses of naturally and experimentally infected hosts to these unique parasite antigens, to identify immunogens that could become vaccine candidates. Immunoprofiling of host serum shows that one particular family (Fam34) elicits a consistent IgG antibody response. This gene family, which we now call Vivaxin, encodes at least 124 transmembrane glycoproteins that display quite distinct expression profiles and patterns of genetic variation. We focused on one gene (viv-β8) that encodes one particularly immunogenic vivaxin protein and which is highly expressed during infections but displays minimal polymorphism across the parasite population. Vaccination of mice with VIVβ8 adjuvanted with Quil-A elicits a strong, balanced immune response and delays parasite proliferation in some animals but, ultimately, it does not prevent disease. Although VIVβ8 is localized across the cell body and flagellar membrane, live immunostaining indicates that VIVβ8 is largely inaccessible to antibody in vivo. However, our phylogenetic analysis shows that vivaxin includes other antigens shown recently to induce immunity against T. vivax. Thus, the introduction of vivaxin represents an important advance in our understanding of the T. vivax cell surface. Besides being a source of proven and promising vaccine antigens, the gene family is clearly an important component of the parasite glycocalyx, with potential to influence host-parasite interactions.

Animal African trypanosomiasis (AAT) is an important livestock disease throughout sub-Saharan Africa and beyond. AAT is caused by Trypanosoma vivax, among other species, a unicellular parasite that is spread by biting tsetse flies and multiplies in the bloodstream and other tissues, leading to often fatal neurological conditions if untreated. Although concerted drug treatment and vector eradication programmes have succeeded in controlling Human African trypanosomiasis, AAT continues to adversely affect animal health and impede efficient food production and economic development in many less-developed countries. In this study, we attempted to identify parasite surface proteins that stimulated the strongest immune responses in naturally infected animals, as the basis for a vaccine. We describe the discovery of a new, species-specific protein family in T. vivax, which we call vivaxin. We show that one vivaxin protein (VIVβ8) is surface expressed and retards parasite proliferation when used to immunize mice, but does not prevent infection. Nevertheless, we also reveal that vivaxin includes another protein previously shown to induce protective immunity (IFX/VIVβ1). Besides its great potential for novel approaches to AAT control, the vivaxin family is revealed as a significant component of the T. vivax cell surface and may have important, species-specific roles in host interactions.

Diagnosis of animal trypanosomoses: proper use of current tools and future prospects

Reliable diagnostic tools are needed to choose the appropriate treatment and proper control measures for animal trypanosomoses, some of which are pathogenic. Trypanosoma cruzi, for example, is responsible for Chagas disease in Latin America. Similarly, pathogenic animal trypanosomoses of African origin (ATAO), including a variety of Trypanosoma species and subspecies, are currently found in Africa, Latin America and Asia. ATAO limit global livestock productivity and impact food security and the welfare of domestic animals. This review focusses on implementing previously reviewed diagnostic methods, in a complex epizootiological scenario, by critically assessing diagnostic results at the individual or herd level. In most cases, a single diagnostic method applied at a given time does not unequivocally identify the various parasitological and disease statuses of a host. These include "non-infected", "asymptomatic carrier", "sick infected", "cured/not cured" and/or "multi-infected". The diversity of hosts affected by these animal trypanosomoses and their vectors (or other routes of transmission) is such that integrative, diachronic approaches are needed that combine: (i) parasite detection, (ii) DNA, RNA or antigen detection and (iii) antibody detection, along with epizootiological information. The specificity of antibody detection tests is restricted to the genus or subgenus due to cross-reactivity with other Trypanosoma spp. and Trypanosomatidae, but sensitivity is high. The DNA-based methods implemented over the last three decades have yielded higher specificity and sensitivity for active infection detection in hosts and vectors. However, no single diagnostic method can detect all active infections and/or trypanosome species or subspecies. The proposed integrative approach will improve the prevention, surveillance and monitoring of animal trypanosomoses with the available diagnostic tools. However, further developments are required to address specific gaps in diagnostic methods and the sustainable control or elimination of these diseases.

Novel protein candidates for serodiagnosis of African animal trypanosomosis: Evaluation of the diagnostic potential of lysophospholipase and glycerol kinase from Trypanosoma brucei

African trypanosomosis, a parasitic disease caused by protozoan parasites transmitted by tsetse flies, affects both humans and animals in sub-Saharan Africa. While the human form (HAT) is now limited to foci, the animal form (AAT) is widespread and affects the majority of sub-Saharan African countries, and constitutes a real obstacle to the development of animal breeding. The control of AAT is hampered by a lack of standardized and easy-to used diagnosis tools. This study aimed to evaluate the diagnostic potential of TbLysoPLA and TbGK proteins from Trypanosoma brucei brucei for AAT serodiagnosis in indirect ELISA using experimental and field sera, individually, in combination, and associated with the BiP C-terminal domain (C25) from T. congolense. These novel proteins were characterized in silico, and their sequence analysis showed strong identities with their orthologs in other trypanosomes (more than 60% for TbLysoPLA and more than 82% for TbGK). TbLysoPLA displays a low homology with cattle (<35%) and Piroplasma (<15%). However, TbGK shares more than 58% with cattle and between 45–55% with Piroplasma. We could identify seven predicted epitopes on TbLysoPLA sequence and 14 potential epitopes on TbGK. Both proteins were recombinantly expressed in Escherichia coli. Their diagnostic potential was evaluated by ELISA with sera from cattle experimentally infected with T. congolense and with T.b. brucei, sera from cattle naturally infected with T. congolense, T. vivax and T.b. brucei. Both proteins used separately had poor diagnostic performance. However, used together with the BiP protein, they showed 60% of sensitivity and between 87–96% of specificity, comparable to reference ELISA tests. In conclusion, we showed that the performance of the protein combinations is much better than the proteins tested individually for the diagnosis of AAT.

African animal trypanosomiasis (AAT) is an endemic disease in sub-Saharan Africa that hinders the development of livestock production on the continent. The control of the disease is based on chemotherapy, vector control and diagnosis. Misuse, as well as the continuous/regular use of a limited number of anti-trypanosomal drugs, is responsible for the appearance of increasingly drug-resistant strains of trypanosomes. In terms of serological diagnosis, the most efficient test at present suffers from a lack of reagent standardization. Unfortunately, even the most promising candidates fail due to low sensitivity in primately or chronically infected animals. Based on this observation it seems obvious that diagnosis must be revisited. In this study we evaluated the diagnostic potential of two Trypanosoma brucei proteins, TbLysoPLA and TbGK, in indirect ELISA for antibody detection. To provide a proof of concept that the judicious association of immunoreactive proteins could improve the sensitivity and specificity of tests based on recombinant antigens, we used these molecules alone and then in combination, associated or not with the BiP protein of T. congolense. The evaluation in serological diagnosis showed that the two proteins used separately had a poor performance. However, when used together with the BiP protein, they showed a sensitivity of 60% and a specificity between 87 and 96%, comparable to the reference tests. It shows for the first time that the performance of protein combinations is much better than that of the proteins tested individually for the diagnosis of AAT.

A recombinant protein (MyxoTLm) for the serological diagnosis of acute and chronic Trypanosoma vivax infection in cattle

Human trypanosomiases and animal trypanosomoses are caused by distinct protozoan parasites of the genus Trypanosoma. The etiological agents of bovine trypanosomosis (BT) are T. vivax, T. congolense, or T. brucei, whose acute infections are initially characterized by hyperthermia, following moderate to severe anemia, subcutaneous edema, lethargy, reduced milk production, progressive weight loss, enlarged lymph nodes, reproductive disorders and death. Animals that survive the acute phase might recover and progress to the chronic, often asymptomatic, phase of infection. Despite their low sensitivity due to the characteristic low parasitemia, simple and costless direct parasitological examinations are the preferred diagnostic methods for animals. Thus, most of the epidemiological studies of BT are based on serological techniques using crude antigen. In this study, we describe the use of the MyxoTLm recombinant protein as an antigen on serological assays. Anti-T. vivax IgM and anti-T. vivax IgG ELISA assays using purified MyxoTLm revealed specificity rates of 91.30 % and 95.65 % and sensitivity rates of 82.35 % and 88.23 %, respectively, being higher than reported for crude antigens. Also, MyxoTLm demonstrated a good performance to detect IgM (ROC curve area = 0.8568) and excellent performance to detect IgG (ROC curve area = 0.9565) when compared to a crude antigen. T. evansi crude antigen used in the indirect anti-T. vivax IgM ELISA reached 70.58 % sensitivity and 78.26 % specificity, and had a lower test performance (ROC curve area = 0.7363). When applied to the anti-T. vivax IgG ELISA, the crude antigen reached 82.35 % sensitivity and 69.56 % specificity, also presenting a low performance with area under the ROC curve of 0.7570. Therefore, the use of MyxoTLm as an antigen on serological diagnosis of BT revealed to increase the sensitivity and the specificity if compared to crude antigens.

Detection of Paratuberculosis in Dairy Herds by Analyzing the Scent of Feces, Alveolar Gas, and Stable Air

Paratuberculosis is an important disease of ruminants caused by Mycobacterium avium ssp. paratuberculosis (MAP). Early detection is crucial for successful infection control, but available diagnostic tests are still dissatisfying. Methods allowing a rapid, economic, and reliable identification of animals or herds affected by MAP are urgently required. This explorative study evaluated the potential of volatile organic compounds (VOCs) to discriminate between cattle with and without MAP infections. Headspaces above fecal samples and alveolar fractions of exhaled breath of 77 cows from eight farms with defined MAP status were analyzed in addition to stable air samples. VOCs were identified by GC-MS and quantified against reference substances. To discriminate MAP-positive from MAP-negative samples, VOC feature selection and random forest classification were performed. Classification models, generated for each biological specimen, were evaluated using repeated cross-validation. The robustness of the results was tested by predicting samples of two different sampling days. For MAP classification, the different biological matrices emitted diagnostically relevant VOCs of a unique but partly overlapping pattern (fecal headspace: 19, alveolar gas: 11, stable air: 4-5). Chemically, relevant compounds belonged to hydrocarbons, ketones, alcohols, furans, and aldehydes. Comparing the different biological specimens, VOC analysis in fecal headspace proved to be most reproducible, discriminatory, and highly predictive.

Diagnosis and molecular typing of Enterocytozoon bieneusi: the significant role of domestic animals in transmission of human microsporidiosis

Enterocytozoon bieneusi is an obligate intracellular fungus-like parasite with high genetic diversity among mammalian and avian hosts. Based on polymorphism analysis of the ribosomal internal transcribed spacer (ITS), nearly 500 genotypes were identified within E. bieneusi. Those genotypes form several genetic groups that exhibit phenotypic differences in host specificity and zoonotic potential and probably have varying public health implications. Some of the genotypes in Group 1 (e.g., D, EbpC, and Type IV) and Group 2 (e.g., BEB4, BEB6, I, and J) are the most common ones that infect a variety of hosts including humans and thus are of public health importance. By contrast, those genotypes in other genetic groups (Groups 3-11) are mostly restricted to the hosts from which they were originally isolated, which would have unknown or limited impacts on public health. Advances on diagnosis and molecular typing of E. bieneusi are introduced in this review. Genotype distribution pattern of E. bieneusi in major domestic animal groups (pigs, cattle, sheep, goats, cats, and dogs), the role of those animals in zoonotic transmission of microsporidiosis, and food and water as potential vehicles for transmission are interpreted here as well. This review highlights the importance of including more genetic or epidemiological data obtained in the same geographical areas and using more reliable genetic markers to analyze the actual extent of host specificity in E. bieneusi, for the purpose of fully appreciating zoonotic risks of those domestic animals in close contacts with men and enhancing our understanding of the modes of transmission.

High Trypanosoma vivax infection rates in water buffalo and cattle in the Brazilian Lower Amazon

Highly sensitive and accurate molecular diagnostic methods have not yet been employed for livestock trypanosomosis in the Brazilian Lower Amazon although the first reports of Trypanosoma vivax and Trypanosoma evansi in Brazil were in water buffalo (Bubalus bubalis) in this region. The present study assessed trypanosomosis in buffalo and cattle raised in communal and seasonally flooding pastures in the state of Pará using the fluorescent fragment length barcoding (FFLB) method. T. evansi was not detected, but high infection rates of T. vivax and T. theileri were revealed by a simplified FFLB standardized in the present study that discriminates all trypanosome species infective to livestock in South America. T. vivax infection rates detected by TviCATL-PCR were 24.6% for cattle (n = 61) and 28.1% for buffalo (n = 89). Using the FFLB method, overall T. vivax infection rates increased to 59.6% and 44.3% for buffalo and cattle, respectively. Furthermore, the predominance of a single microsatellite-based genotype of T. vivax was reinforced in the Lower Amazon. Relevant T. vivax infection rates detected in clinically healthy buffalo and cattle through the sampled years (2008-2017) highlight the need for systematic studies to demonstrate the endemic steady state of T. vivax in this region. Our findings provide baseline information for livestock management, including control of T. vivax dispersal, and the introduction of naïve animals. The growing international trade of live livestock from this very important livestock breeding region represents a serious risk for T. vivax spreading outside Amazonia and Brazil.

Product Development Partnerships: Delivering Innovation for the Elimination of African Trypanosomiasis?

African trypanosomiasis has been labelled as a 'tool-deficient' disease. This article reflects on the role that Product Development Partnerships (PDPs) have played in delivering new tools and innovations for the control and elimination of the African trypanosomiases. We analysed three product development partnerships-DNDi, FIND and GALVmed-that focus on delivering new drugs, diagnostic tests, and animal health innovations, respectively. We interviewed key informants within each of the organisations to understand how they delivered new innovations. While it is too early (and beyond the scope of this article) to assess the role of these three organisations in accelerating the elimination of the African trypanosomiases, all three organisations have been responsible for delivering new innovations for diagnosis and treatment through brokering and incentivising innovation and private sector involvement. It is doubtful that these innovations would have been delivered without them. To varying degrees, all three organisations are evolving towards a greater brokering role, away from only product development, prompted by donors. On balance, PDPs have an important role to play in delivering health innovations, and donors need to reflect on how best to incentivise them to focus and continue to deliver new products.

Expression and copper binding properties of the N-terminal domain of copper P-type ATPases of African trypanosomes

Copper is an essential component of cuproproteins but can be toxic to cells, therefore copper metabolism is very carefully regulated within cells. To gain insight into trypanosome copper metabolism, Trypanosoma spp. genomic databases were screened for the presence of copper-containing and -transporting proteins. Among other genes encoding copper-binding proteins, a copper-transporting P-type ATPase (CuATPase) gene was identified. Sequence and phylogenetic analyses suggest that the gene codes for a Cu⁺ transporter belonging to the P_1B-1 ATPase subfamily that has an N-terminal domain with copper binding motifs. The N-terminal cytosolic domains of the proteins from Trypanosoma congolense and Trypanosoma brucei brucei were recombinantly expressed in Escherichia coli as maltose binding protein (MBP) fusion proteins. These N-terminal domains bound copper in vitro and within E. coli cells, more than the control MBP fusion partner alone. The copper binding properties of the recombinant proteins were further confirmed when they inhibited copper catalysed ascorbate oxidation. Native CuATPases were detected in a western blot of lysates of T. congolense IL3000 and T. b. brucei ILTat1.1 bloodstream form parasites using affinity purified IgY antibodies against N-terminal domain peptides. The CuATPase was also detected by immunofluorescence in T. b. brucei bloodstream form parasites where it was associated with subcellular vesicles. In conclusion, Trypanosoma species express a copper-transporting P_1B-1-type ATPase and together with other copper-binding proteins identified in the genomes of kinetoplastid parasites may constitute potential targets for anti-trypanosomal drug discovery.

Parasite specific 7SL-derived small RNA is an effective target for diagnosis of active trypanosomiasis infection

Human and animal African trypanosomiasis (HAT & AAT, respectively) remain a significant health and economic issue across much of sub-Saharan Africa. Effective control of AAT and potential eradication of HAT requires affordable, sensitive and specific diagnostic tests that can be used in the field. Small RNAs in the blood or serum are attractive disease biomarkers due to their stability, accessibility and available technologies for detection. Using RNAseq, we have identified a trypanosome specific small RNA to be present at high levels in the serum of infected cattle. The small RNA is derived from the non-coding 7SL RNA of the peptide signal recognition particle and is detected in the serum of infected cattle at significantly higher levels than in the parasite, suggesting active processing and secretion. We show effective detection of the small RNA in the serum of infected cattle using a custom RT-qPCR assay. Strikingly, the RNA can be detected before microscopy detection of parasitaemia in the blood, and it can also be detected during remission periods of infection when no parasitaemia is detectable by microscopy. However, RNA levels drop following treatment with trypanocides, demonstrating accurate prediction of active infection. While the small RNA sequence is conserved between different species of trypanosome, nucleotide differences within the sequence allow generation of highly specific assays that can distinguish between infections with Trypanosoma brucei, Trypanosoma congolense and Trypanosoma vivax. Finally, we demonstrate effective detection of the small RNA directly from serum, without the need for pre-processing, with a single step RT-qPCR assay. Our findings identify a species-specific trypanosome small RNA that can be detected at high levels in the serum of cattle with active parasite infections. This provides the basis for the development of a cheap, non-invasive and highly effective diagnostic test for trypanosomiasis.

African trypanosomes cause significant disease in humans and animals across sub-Saharan Africa. For both human and animal infections diagnostics that can accurately identify an active infection are lacking–this is particularly the case in animal disease where most diagnosis is based upon clinical signs, which is not a specific or sensitive means of detecting infection. There is therefore a significant unmet need for a pathogen marker of active infection that accurately indicates whether an animal or human is currently infected. Through analysing the blood of cattle infected with trypanosomes, we identified a short sequence of RNA that was present at very high levels. This small RNA derives from the trypanosome genome, and we could identify its presence in the genome of all three species that are responsible for human and animal disease. We were able to design species-specific tests, and showed that in samples from infected animals the assays were more sensitive than the traditional microscope-based detection, importantly the signal disappeared relatively quickly after successful treatment, and when treatment failed, the assay was able to accurately identify when infection persisted. We also demonstrated that the causative agent of human trypanosomiasis secretes the marker at similar levels to that seen in the animal-infective trypanosomes. Therefore, we have discovered a marker of trypanosome infection that is present at high levels in the blood of infected animals, disappears quickly upon successful treatment, but is effective at detecting instances of unsuccessful treatment and persistent infection. This represents a potentially powerful diagnostic tool for human and animal trypanosomiasis.

Trypanosoma vivax infection in sheep: Different patterns of virulence and pathogenicity associated with differentially expressed proteomes

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Trypanosoma vivax strains exhibit different virulence and pathogenicity patterns.

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TvMT1 strain showed low virulence and high pathogenicity.

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TvLIEM176 strain showed high virulence and moderate pathogenicity.

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Protein expression varies in high virulence/moderate pathogenicity strain vs low virulence/high pathogenicity strain.

Cattle trypanosomosis caused by Trypanosoma vivax is a widely distributed disease in Africa and Latin America. It causes significant losses in the livestock industry and is characterized by fluctuating parasitemia, anemia, fever, lethargy, and weight loss. In this study we evaluated the virulence (capacity to multiply inside the host and to modulate the host response) and pathogenicity (ability to produce disease and/or mortality) patterns of two T. vivax strains (TvMT1 and TvLIEM176) in experimentally-infected sheep and determined the proteins differentially expressed in the proteomes of these two strains. Hematological and clinical parameters were monitored in experimentally-infected versus non-infected sheep for 60 days. All the infected animals developed discernable parasitemia at 3 days post-infection (dpi), and the first parasitemia peak was observed at 6 dpi. The maximum average value of parasitemia was 1.3 × 10⁷ (95% CI, 7.9 × 10⁵–2 × 10⁸) parasites/ml in TvLIEM176-infected animals, and 2.5 × 10⁶ (95% CI, 1.6 × 10⁵–4 × 10⁷) parasites/ml in TvMT1-infected ones. Anemia and clinical manifestations were more severe in the animals infected by TvMT1 strain than in those infected by TvLIEM176. In the proteomic analysis, a total of 29 proteins were identified, of which 14 exhibited significant differences in their expression levels between strains. Proteins with higher expression in TvLIEM176 were: alpha tubulin, beta tubulin, arginine kinase, glucose-regulated protein 78, paraflagellar protein 3, and T-complex protein 1 subunit theta. Proteins with higher expression in TvMT1 were: chaperonin HSP60, T-complex protein 1 subunit alpha, heat shock protein 70, pyruvate kinase, glycerol kinase, inosine-5'-monophosphate dehydrogenase, 73 kDa paraflagellar rod protein, and vacuolar ATP synthase. There was a difference in the virulence and pathogenicity between the T. vivax strains: TvLIEM176 showed high virulence and moderate pathogenicity, whereas TvMT1 showed low virulence and high pathogenicity. The proteins identified in this study are discussed for their potential involvement in strains’ virulence and pathogenicity, to be further defined as biomarkers of severity in T. vivax infections.

Recombinant and native TviCATL from Trypanosoma vivax: Enzymatic characterisation and evaluation as a diagnostic target for animal African trypanosomosis

African animal trypanosomosis (nagana) is caused by tsetse-transmitted protozoan parasites. Their cysteine proteases are potential chemotherapeutic and diagnostic targets. The N-glycosylated catalytic domain of Trypanosoma vivax cathepsin L-like cysteine protease, rTviCATL_cat, was recombinantly expressed and purified from culture supernatants while native TviCATL was purified from T. vivax Y486 parasite lysates. Typical of Clan CA, family C₁ proteases, TviCATL activity is sensitive to E-64 and cystatin and substrate specificity is defined by the S₂ pocket. Leucine was preferred in P₂ and basic and non-bulky, hydrophobic residues accepted in P₁ and P₃ respectively. Reversible aldehyde inhibitors, antipain, chymostatin and leupeptin, with Arg in P₁ and irreversible peptidyl chloromethylketone inhibitors with hydrophobic residues in P₂ inhibited TviCATL activity. TviCATL digested host proteins: bovine haemoglobin, serum albumin, fibrinogen and denatured collagen (gelatine) over a wide pH range, including neutral to slightly acidic pH. The recombinant catalytic domain of TviCATL showed promise as a diagnostic target for detecting T. vivax infection in cattle in an indirect antibody detection ELISA.

Development of a Nanobody-based lateral flow assay to detect active Trypanosoma congolense infections

Animal African trypanosomosis (AAT), a disease affecting livestock, is caused by parasites of the Trypanosoma genus (mainly T. vivax and T. congolense). AAT is widespread in Sub-Saharan Africa, where it continues to impose a heavy socio-economic burden as it renders development of sustainable livestock rearing very strenuous. Active case-finding and the identification of infected animals prior to initiation of drug treatment requires the availability of sensitive and specific diagnostic tests. In this paper, we describe the development of two heterologous sandwich assay formats (ELISA and LFA) for T. congolense detection through the use of Nanobodies (Nbs). The immunisation of an alpaca with a secretome mix from two T. congolense strains resulted in the identification of a Nb pair (Nb44/Nb42) that specifically targets the glycolytic enzyme pyruvate kinase. We demonstrate that the Nb44/Nb42 ELISA and LFA can be employed to detect parasitaemia in plasma samples from experimentally infected mice and cattle and, additionally, that they can serve as ‘test-of-cure’ tools. Altogether, the findings in this paper present the development and evaluation of the first Nb-based antigen detection LFA to identify active T. congolense infections.

A comparative in silico linear B-cell epitope prediction and characterization for South American and African Trypanosoma vivax strains

Trypanosoma vivax is a parasite widespread across Africa and South America. Immunological methods using recombinant antigens have been developed aiming at specific and sensitive detection of infections caused by T. vivax. Here, we sequenced for the first time the transcriptome of a virulent T. vivax strain (Lins), isolated from an outbreak of severe disease in South America (Brazil) and performed a computational integrated analysis of genome, transcriptome and in silico predictions to identify and characterize putative linear B-cell epitopes from African and South American T. vivax. A total of 2278, 3936 and 4062 linear B-cell epitopes were respectively characterized for the transcriptomes of T. vivax LIEM-176 (Venezuela), T. vivax IL1392 (Nigeria) and T. vivax Lins (Brazil) and 4684 for the genome of T. vivax Y486 (Nigeria). The results presented are a valuable theoretical source that may pave the way for highly sensitive and specific diagnostic tools.

Structural basis for the high specificity of a Trypanosoma congolense immunoassay targeting glycosomal aldolase

BACKGROUND

Animal African trypanosomosis (AAT) is a neglected tropical disease which imposes a heavy burden on the livestock industry in Sub-Saharan Africa. Its causative agents are Trypanosoma parasites, with T. congolense and T. vivax being responsible for the majority of the cases. Recently, we identified a Nanobody (Nb474) that was employed to develop a homologous sandwich ELISA targeting T. congolense fructose-1,6-bisphosphate aldolase (TcoALD). Despite the high sequence identity between trypanosomatid aldolases, the Nb474-based immunoassay is highly specific for T. congolense detection. The results presented in this paper yield insights into the molecular principles underlying the assay's high specificity.

METHODOLOGY/PRINCIPAL FINDINGS

The structure of the Nb474-TcoALD complex was determined via X-ray crystallography. Together with analytical gel filtration, the structure reveals that a single TcoALD tetramer contains four binding sites for Nb474. Through a comparison with the crystal structures of two other trypanosomatid aldolases, TcoALD residues Ala77 and Leu106 were identified as hot spots for specificity. Via ELISA and surface plasmon resonance (SPR), we demonstrate that mutation of these residues does not abolish TcoALD recognition by Nb474, but does lead to a lack of detection in the Nb474-based homologous sandwich immunoassay.

CONCLUSIONS/SIGNIFICANCE

The results show that the high specificity of the Nb474-based immunoassay is not determined by the initial recognition event between Nb474 and TcoALD, but rather by its homologous sandwich design. This (i) provides insights into the optimal set-up of the assay, (ii) may be of great significance for field applications as it could explain the potential detection escape of certain T. congolense strains, and (iii) may be of general interest to those developing similar assays.