Novel diagnostic tests for human African trypanosomiasis: what is their role in primary health care services?
Thesis summary
Introduction
The control of human African trypanosomiasis (HAT) is mainly based on active case detection (i.e. population screening) and treatment of cases. This strategy is very effective when it combines the serological screening test “CATT” with sensitive parasitological confirmation techniques for case detection in a rigorously applied repeated exhaustive population screening. National control programs rely on specialized mobile teams for these active case detection campaigns. Over the last 15 years, this strategy led to a remarkable decrease in reported case numbers, and a WHO expert committee recently considered the possibility of the elimination of HAT as a reachable goal by 2020. The decreasing HAT case burden has also led to calls for integration of HAT control into the primary health care (PHC) system.
However, most of the primary health care facilities in the endemic areas in West-and Central-Africa suffer several shortcomings, notably in equipment, supplies and basic infrastructure to take care of a disease that was so far always managed by specialized structures. Assigning the case management duties for a sleeping sickness patient to this level of the health system would require substantial strengthening of capacities at this level.
Furthermore, over the last decade significant investments were made in the development of new diagnostic tools and (oral) drugs for HAT which – if validated – can make substantial contributions to the management of HAT patients in the primary health care facilities. Several promising diagnostic tools as a novel format of the CATT, the CATT D10, a user-friendly nucleic acid based- assay, the LAMP, etc. were proposed, but their effectiveness and feasibility for the specific context of the primary care facilities remained to be demonstrated.
My PhD project set out to evaluate these novel technologies on its potential usefulness in the primary health care facilities.
Objectives
The overall goal of the thesis is to contribute to improved case management of HAT patients. Our hypothesis is that a target product profile described in the ASSURED criteria has helped to shape more user-friendly and simple diagnostic technology that indeed can lead to better diagnosis and care of HAT patients in the health services. Our specific objectives are: 1) To review the existing diagnostic tests which can safely be used in the primary health care facilities; 2) To evaluate several promising new diagnostic tests that can be used in the primary health care facilities and 3) To study the level of attainment of integration of HAT case detection and management in primary care centres in two high-prevalence districts in the province of Bandundu, DRC
Methods
Most of our research work took place in the DRC and Belgium. To address the first specific objective, we conducted a systematic review of the literature on existing diagnostic tests for HAT. For the second specific objective we conducted a number of diagnostic accuracy studies to estimate sensitivity, specificity and reproducibility characteristics of several tools: CATT D10, LED-based fluorescence microscopy, and LAMP. Finally, we studied the level of attainment of integration of HAT case detection and management in primary care centres in two high-prevalence districts in the province of Bandundu, DRC.
Results
Human African trypanosomiasis diagnosis in first-line health services of endemic countries, a systematic review
Our systematic literature review retrieved 16 different screening and confirmation tests for HAT. The thermostable format of the Card Agglutination Test for Trypanosomiasis (CATT test) was the most appropriate screening test at that point in time. Lateral flow antibody detection tests show clear promise as alternative screening tests in the near future. Confirmation of HAT diagnosis still depends on visualizing the parasite in direct microscopy. All other currently available confirmation tests are either technically too demanding and/or lack sensitivity and are thus rather inappropriate for use at health center level.Novel applications of molecular tests may have potential for use at district hospital level in the future.
A new format of the CATT test for the detection of HAT, designed for use in peripheral health facilities
We found that inter-format reproducibility of CATT-D10 vs. CATT-R250 on whole blood performed by laboratory technicians in the field was excellent with kappa values of 0.83–0.89. Both inter- and intra-format reproducibility assessed by CATT titration were excellent, with 96.5–100% of all differences observed falling within the limits of ± one titration step. After 18 months, reactivity of test kits incubated under all fourtemperature regimens was still well above the minimum threshold considered acceptable. The CATT-D10 is thermostable and can be used interchangeably with the old format of the CATT test. Although, the wastage of the reagent is inevitable, it is suitable for use in peripheral health facilities in HAT-endemic countries.
Improved Detection of Trypanosoma brucei by Lysis of Red Blood Cells (RBC), Concentration and LED Fluorescence Microscopy
Detection of parasites was significantly improved by RBC lysis and concentration, regardless of the staining and microscopy method used. Further improvements were made when smears were prepared using larger volumes of sediment. The best results were obtained with thin smears prepared using 20 µl of sediment and stained with Acridine Orange (AO). The time taken to see the first parasite was dramatically reduced when smears were examined by LED microscopy, compared to bright light. LED fluorescence microscopy was found to be easier and requiring less visual effort than bright field microscopy. These studies demonstrate the potential for an incremental improvement in detection of Trypanosoma brucei by combining LED fluorescence microscopy with RBC lysis and concentration. The lysis and concentration method may also be useful in sample preparation for other diagnostic tests for trypanosomiasis.
Improved Detection of Sleeping Sickness Cases by LED Fluorescence Microscopy (FM): Evidence from a Prospective Multicentric Study in the DRC
We observed that the sensitivity of FM using thick blood smears stained with AO was 3 times higher than bright field microscopy using Giemsa-stained thick blood smears: 19.7% (95% CI: 14.9-25.6%) versus 6.1% (95% CI: 3.6-10.2%). When the RBC lysis and concentration procedure was included, test sensitivity was further enhanced to 23.0% (95% CI: 17.9-29.1%) with thick blood smears and 34.3% (95% CI: 28.2-40.9%) with thin blood smears. Specificity of all fourmicroscopy methods was 100% (95% CI: 96.1-100.0%). However, the miniature Anion Exchange Chromatography (mAECT) and Capillary Tube Centrifugation (CTC) methods remained more sensitive.These new FM methods have practical advantages, such as a shorter staining time, ease of demonstration of parasites and the possibility of archiving slides for a control quality system. They should be considered as alternative methods to enhance case detection where concentration procedures such as mAECT or CTC are not available.
Diagnostic accuracy of LoopampTM Trypanosoma brucei Detection Kit for Diagnosis of HAT in Clinical samples
We observed good sensitivity of LAMP with a 95% C.I. of 80.9%-96.1%. Specificity in healthy controls wasestimated 86.4 to 98.6% (95% CI). The reproducibility was excellent with a kappa value of 0.81. The LAMP showed good diagnostic accuracy and excellent reproducibility. Further studies are needed to assess the feasibility of its routine use for diagnosis of HAT under field conditions.
Integration of diagnosis and treatment of sleeping sickness in primary health care facilities in the Democratic Republic of the Congo
We observed that all health centers were operating, but most were poorly equipped and attendance rates were very low. The staff has a good knowledge of presenting symptoms, diagnosis and treatment of both HAT and tuberculosis. We observed a median of 14 outpatient consultations per facility (interquartile range 8-21) in the week prior to our visit, i.e. 2 per day. Ninecenters were designated HAT diagnosis and treatment centers but the most sensitive diagnostic test, the mini anion exchange centrifugation technique (mAECT) was not present in any. Though all 9were performing the CATT screening test, only 2 had the required cold chain in order. In these high prevalence districts in DRC staff are well aware of HAT but they lack the tools required for an adequate diagnostic procedure. Moreover attendance rates are extremely low, making it unlikely that a resurgence of HAT will be recognized timely.
Discussion
The HAT remains to this day a health problem in the DRC even if the prevalence has fallen substantially in recent years. These results are related by an intensive effort of exhaustive active and passive case finding activities. To consolidate these achievements, WHO and its panel of experts evoke the elimination of the disease. However, in the situation of very low prevalence, active case finding becomes inefficient and only passive case finding is referred as an alternative approach that can ensure the sustainability of long-term surveillance of the disease. The integration of new diagnostic tools such as LAMP, RDT and the new safe oral treatment in the general peripheral health services in remote areas, can not only increase access to diagnosis and treatment of patients but also represent an important step towards the elimination of the disease.
Conclusion and recommendations
The health system is not functional. Given the advent of new oral drugs that are active in the first and second stage, ease to handle, the general health services must undergo far-reaching changes which will allow them to play a vital role in HAT surveillance. Research on alternative strategies of surveillance of HAT are needed because passive case finding alone is not suitable for early detection of resurgence of the disease.