Development of ELISAs for diagnosis of acute typhoid fever in Nigerian children

Isolation and characterization of DNA aptamers against the HlyE antigen of Salmonella Typhi

Aptamers have emerged as prominent ligands in clinical diagnostics because they provide various advantages over antibodies, such as quicker generation time, reduced manufacturing costs, minimal batch-to-batch variability, greater modifiability, and improved thermal stability. In the present study, we isolated and characterized DNA aptamers that can specifically bind to the hemolysin E (HlyE) antigen of Salmonella Typhi for future development of typhoid diagnostic tests. The DNA aptamers against Salmonella Typhi HlyE were isolated using systematic evolution of ligands by exponential enrichment (SELEX), and their binding affinity and specificity were assessed utilizing enzyme-linked oligonucleotide assay (ELONA). A total of 11 distinct aptamers were identified, and the binding affinities and species selectivities of the three most probable aptamers were determined. Kd values were obtained in the nanomolar range, with the highest affinity of 83.6 nM determined for AptHlyE97. In addition, AptHlyE11, AptHlyE45 and AptHlyE97 clearly distinguished S. Typhi HlyE from other tested bacteria, such as Salmonella Paratyphi A, Salmonella Paratyphi B, Shigella flexneri, Klebsiella pneumonia and Escherichia coli, therefore displaying desirable specificity. These novel aptamers could be used as diagnostic ligands for the future development of inexpensive and effective point-of-care tests for typhoid surveillance, especially in developing countries of the tropics and subtropics.

The Prevalence of Undiagnosed Salmonella enterica Serovar Typhi in Healthy School-Aged Children in Osun State, Nigeria

Typhoid fever remains a significant public health concern due to cases of mis-/overdiagnosis. Asymptomatic carriers play a role in the transmission and persistence of typhoid fever, especially among children, where limited data exist in Nigeria and other endemic countries. We aim to elucidate the burden of typhoid fever among healthy school-aged children using the best surveillance tool(s). In a semi-urban/urban state (Osun), 120 healthy school-aged children under 15 years were enrolled. Whole blood and fecal samples were obtained from consenting children. ELISA targeting the antigen lipopolysaccharide (LPS) and anti-LPS antibodies of Salmonella Typhi, culture, polymerase chain reaction (PCR), and next-generation sequencing (NGS) were used to analyze the samples. At least one of the immunological markers was detected in 65.8% of children, with 40.8%, 37.5%, and 39% of children testing positive for IgM, IgG, and antigen, respectively. Culture, PCR, and NGS assays did not detect the presence of Salmonella Typhi in the isolates. This study demonstrates a high seroprevalence of Salmonella Typhi in these healthy children but no carriage, indicating the inability to sustain transmission. We also demonstrate that using a single technique is insufficient for typhoid fever surveillance in healthy children living in endemic areas.

Surface-enhanced Raman spectroscopy for characterization of filtrate portions of blood serum samples of typhoid patients

BACKGROUND

Surface-enhanced Raman spectroscopy (SERS) is explored to design a rapid screening method for the characterization and diagnosis of typhoid fever by employing filtrate fractions of blood serum samples obtained by centrifugal filtration with 50 KDa filters.

OBJECTIVES

The purpose of this study, to separate the filtrate portions of blood serum samples in this way contain proteins smaller than 50 kDa and removal of bigger size protein which allows to acquire the SERS spectral features of smaller proteins more effectively which are probably associated with typhoid disease. Disease caused by Salmonella typhi diagnose more effectively by using surface-enhanced Raman spectroscopy (SERS) and multivariate data analysis tools.

METHODS

SERS was used as a diagnostic tool for typhoid fever by comparison between healthy and diseased samples. For this purpose, all the samples were analyzed by comparing their SERS spectral features. Over the spectral range of 400-1800cm^-1, multivariate data analysis techniques such as Principal Component Analysis (PCA) and Partial Least Squares-Discriminant Analysis (PLS-DA) are applied to diagnose and differentiate different filtrate fractions of blood serum samples of patients of typhoid fever and healthy ones.

RESULTS

By comparing SERS spectra of healthy filtrate with that of filtrate of typhoid sample, the SERS spectral features associated with disease development are identified including PCA is found to be efficient for the qualitative differentiation of all of the samples analyzed. Moreover, PLS-DA successfully identified and classified healthy and typhoid positive blood serum samples with 97 % accuracy, 99 % specificity, 91 % sensitivity and 0.78 area under the receiver operating characteristic (AUROC) curve.

CONCLUSIONS

Surface enhanced Raman spectroscopy using silver nanoparticles SERS substrate, is found to be useful technique for the quick identification and evaluation of filtrate fractions of the blood serum samples of healthy and typhoid samples for disease diagnosis.

Two-Color Duplex Platform for Point-of-Care Differential Detection of Malaria and Typhoid Fever

Malaria and typhoid fever are two febrile illnesses prevalent in the tropics that often present overlapping symptoms. In this work, we demonstrate an optical reader-based diagnostics platform for rapid codetection and quantification of two antigen targets: lipopolysaccharide (LPS) for typhoid fever and plasmodium lactate dehydrogenase (pLDH) for malaria infections. We report a limit of detection (LoD) of 5 ng/mL for LPS and 10 ng/mL for pLDH in a spiked serum test. We also validated the duplex test's performance of differentiating malaria infection, typhoid fever infection, and coinfection by testing clinical samples in human serum. Our platform provides the potential for further multiplexing by encoding different color codes to various detection targets. The rapid result (∼15 min), low cost (∼$2), and minimal volume requirement for human serum clinical samples (4 μL) of our diagnostic platform offer great potential for deployment in resource-limited settings to help distinguish common causes for acute febrile illnesses at the point-of-need.

Performance of Immunodiagnostic Tests for Typhoid Fever: A Systematic Review and Meta-Analysis

Typhoid fever, also known as typhoid, is a life-threatening bacterial infection that remains a global health concern. The infection is associated with a significant morbidity and mortality rate, resulting in an urgent need for specific and rapid detection tests to aid prevention and management of the disease. The present review aims to assess the specificity and sensitivity of the available literature on the immunodiagnostics of typhoid fever. A literature search was conducted using three databases (PubMed, ProQuest and Scopus) and manual searches through the references of identified full texts to retrieve relevant literature published between 1 January 2011 and 31 December 2020. Of the 577 studies identified in our search, 12 were included in further analysis. Lipopolysaccharides (LPS) and hemolysin E (HlyE) were the most frequently studied antigens. The specimens examined in these studies included serum and saliva. Using blood culture as the gold standard, anti-LPS IgA gave the highest sensitivity of 96% (95% CI: 93–99) and specificity of 96% (95% CI: 93–99) for distinguishing between typhoid cases and healthy controls, whereas the combination of anti-LPS and anti-flagellin total IgGAM gave the highest sensitivity of 93% (95% CI: 86–99) and specificity of 95% (95% CI: 89–100) for distinguishing typhoid cases and other febrile infections. A comparably high sensitivity of 92% (95% CI: 86–98) and specificity of 89% (95% CI: 78–100) were shown in testing based on detection of the combination of anti-LPS (IgA and IgM) and anti-HlyE IgG as well as a slightly lower sensitivity of 91% (95% CI: 74–100) in the case of anti-50kDa IgA. Anti-50kDa IgM had the lowest sensitivity of 36% (95% CI: 6–65) against both healthy and febrile controls. The development of a rapid diagnostic test targeting antibodies against lipopolysaccharides combined with flagellin appeared to be a suitable approach for the rapid detection test of typhoid fever. Saliva is added benefit for rapid typhoid diagnosis since it is less invasive. As a result, further studies could be done to develop additional approaches for adopting such samples.

Enteric Fever Diagnosis: Current Challenges and Future Directions

Enteric fever is a life-threatening systemic febrile disease caused by Salmonella enterica serovars Typhi and Paratyphi (S. Typhi and S. Paratyphi). Unfortunately, the burden of the disease remains high primarily due to the global spread of various drug-resistant Salmonella strains despite continuous advancement in the field. An accurate diagnosis is critical for effective control of the disease. However, enteric fever diagnosis based on clinical presentations is challenging due to overlapping symptoms with other febrile illnesses that are also prevalent in endemic areas. Current laboratory tests display suboptimal sensitivity and specificity, and no diagnostic methods are available for identifying asymptomatic carriers. Several research programs have employed systemic approaches to identify more specific biomarkers for early detection and asymptomatic carrier detection. This review discusses the pros and cons of currently available diagnostic tests for enteric fever, the advancement of research toward improved diagnostic tests, and the challenges of discovering new ideal biomarkers and tests.

Evaluation of Salmonella Typhi antigen YncE alongside HlyE for the detection of typhoid fever and its carriers

Typhoid fever is a disease caused by Salmonella Typhi that was implicated in millions of illnesses worldwide annually. Individuals that do not recover fully from typhoid fever can become asymptomatic carriers of the disease. Host antibodies against the S. Typhi antigens, HlyE (for acute typhoid) and YncE (for carriers) were previously reported to be useful biomarkers for the disease. Here, we expressed and purified recombinant HlyE and YncE antigens and tested the IgG, IgA and IgM responses in 422 sera samples retrieved from acute typhoid patients, other febrile, food handlers, and healthy individuals. The results showed that HlyE-IgG, -IgA and -IgM ELISAs have a collective sensitivity of 83% while YncE-IgG and -IgA ELISAs identified 16 possible carriers based on their antibody profiles. The identification of sensitive biomarkers for typhoid carrier detection is crucial for disease eradication.

Redefining typhoid diagnosis: what would an improved test need to look like?

INTRODUCTION

Typhoid fever is one of the most common bacterial causes of acute febrile illness in the developing world, with an estimated 10.9 million new cases and 116.8 thousand deaths in 2017. Typhoid point-of-care (POC) diagnostic tests are widely used but have poor sensitivity and specificity, resulting in antibiotic overuse that has led to the emergence and spread of multidrug-resistant strains. With recent advances in typhoid surveillance and detection, this is the ideal time to produce a target product profile (TPP) that guides product development and ensure that a next-generation test meets the needs of users in the resource-limited settings where typhoid is endemic.

METHODS

A structured literature review was conducted to develop a draft TPP for a next-generation typhoid diagnostic test with minimal and optimal desired characteristics for 36 test parameters. The TPP was refined using feedback collected from a Delphi survey of key stakeholders in clinical medicine, microbiology, diagnostics and public and global health.

RESULTS

A next-generation typhoid diagnostic test should improve patient management through the diagnosis and treatment of infection with acute Salmonella enterica serovars Typhi or Paratyphi with a sensitivity ≥90% and specificity ≥95%. The test would ideally be used at the lowest level of the healthcare system in settings without a reliable power or water supply and provide results in <15 min at a cost of

CONCLUSION

This report outlines the first comprehensive TPP for typhoid fever and is intended to guide the development of a next-generation typhoid diagnostic test. An accurate POC test will reduce the morbidity and mortality of typhoid fever through rapid diagnosis and treatment and will have the greatest impact in reducing antimicrobial resistance if it is combined with diagnostics for other causes of acute febrile illness in a treatment algorithm.

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Key Words

• Other diagnostic or tool
• Public Health
• diagnostics and tools
• typhoid and paratyphoid fevers

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MESH Headings Collapse

Grants

• Department for International Development

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Affiliation(s)

Richard G Mather Malaria and Fever Program, Foundation for Innovative New Diagnostics (FIND), Geneva, Switzerland Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK
Heidi Hopkins Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK
Christopher M Parry Department of Clinical Sciences, Liverpool School of Tropical Medicine, Liverpool, UK School of Tropical Medicine and Global Health, Nagasaki University, Nagasaki, Japan
Sabine Dittrich Malaria and Fever Program, Foundation for Innovative New Diagnostics (FIND), Geneva, Switzerland Nuffield Department of Medicine, University of Oxford, Oxford, UK

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Plasma Immunoglobulin A Responses Against 2 Salmonella Typhi Antigens Identify Patients With Typhoid Fever

BACKGROUND

There is a need for a reliable, simple diagnostic assay for typhoid fever. Available commercial serologic assays for typhoid fever have limited sensitivity and specificity. Using high-throughput immunoscreening technologies, we previously identified several immunoreactive Salmonella Typhi antigens that seem promising for possible inclusion in a new diagnostic assay: hemolysin E (HlyE), cytolethal distending toxin, S. Typhi lipopolysaccharide (LPS), and S. Typhi membrane preparation.

METHODS

We assessed plasma antibody responses (immunoglobulin [Ig] M, IgA, and IgG) to these antigens by means of enzyme-linked immunosorbent assay in patients with suspected enteric fever, controls with other febrile illnesses, and healthy controls in Dhaka, Bangladesh and performed Tubex and Typhidot tests, the Widal assay, and the typhoid/paratyphoid test (TPTest) in each patient. Using machine learning methods, we identified a parsimonious serology signature to distinguish acute typhoid cases from controls and then validated our findings in an independent test cohort from Nepal of patients with culture-confirmed S. Typhi and controls with other bacteremic illnesses.

RESULTS

We demonstrated that the use of 2 antigens (HlyE and LPS) with 1 antibody isotype (IgA) could distinguish typhoid from other invasive bacterial infections (area under the receiver operating characteristic curve [AUC], 0.95; sensitivity, 90%, specificity, 92%). Use of a single antigen (HlyE) and isotype (IgA) had an AUC of 0.93.

CONCLUSION

Our results suggest that development of a diagnostic assay for acute typhoid fever focused on detecting IgA responses against HlyE, with or without LPS, is warranted.

Economic evaluation of typhoid - a review

INTRODUCTION

To evaluate the potential economic value and likely impact of a hypothetical rapid test in its early stages of development requires the use of models. The model structure and the type of model (dynamic/static) to employ are key considerations. The aim of the review was to explore the literature on typhoid economic evaluations and to explore the types of models that have been previously adopted in this setting for test-treat evaluations and to capture data on model inputs that may be useful for a de novo model.

AREAS COVERED

A systematic review was conducted to identify economic evaluations focused on typhoid in established literature databases. Eight studies were identified and included for narrative synthesis. The review has revealed that there have been relatively few economic evaluations that have focused on typhoid fever, all of which have focused on the impact of interventions at the population level (vaccination) but not the individual level (test-treat strategies).

EXPERT COMMENTARY

Under certain circumstances, either a static model or a transmission dynamic model may be appropriate in the evaluation of an intervention for typhoid fever. Typhoid test-treat modeling represents a gray area where further work is needed.

Typhoid Fever Diagnosis in Endemic Countries: A Clog in the Wheel of Progress?

Typhoid fever causes significant morbidity and mortality in developing countries, with inaccurate estimates in some countries affected, especially those situated in Sub-Saharan Africa. Disease burden assessment is limited by lack of a high degree of sensitivity and specificity by many current rapid diagnostic tests. Some of the new technologies, such as PCR and proteomics, may also be useful but are difficult for low-resource settings to apply as point-of-care diagnostics. Weak laboratory surveillance systems may also contribute to the spread of multidrug resistant Salmonella serovar Typhi across endemic areas. In addition, most typhoid-endemic countries employ serological tests that have low sensitivity and specificity making diagnosis unreliable. Here we review currently available typhoid fever diagnostics, and advances in serodiagnosis of S. Typhi.