Human African trypanosomiasis

Human African trypanosomiasis (HAT), or sleeping sickness, is a life-threatening neglected tropical infection affecting rural populations in sub-Saharan Africa. In West and Central Africa, chronic trypanosomiasis is caused by Trypanosoma brucei gambiense infection.(1) Control of the disease has been facilitated by the use of the card agglutination test for trypanosomiasis, which is particularly suited for large-scale screening of the populations at risk.(2) With the steadily decreasing prevalence of trypanosomiasis, individual rapid diagnostic tests that can be used in primary health centers, that are stable at ambient temperatures, and that are highly specific have become a research priority.(1)

We developed two rapid diagnostic tests for trypanosomiasis caused by T. brucei gambienseinfection. The HAT Sero-Strip and HAT Sero-K-SeT tests detect trypanosome-specific antibodies and are, respectively, a dipstick and a lateral-flow device for testing blood (30 μl) or plasma (15 μl); both tests provide results in 15 minutes. The tests contain variant surface glycoproteins of the T. brucei gambiense variable antigen types LiTat 1.3 and LiTat 1.5.(3)

Evaluation of the test

The tests were evaluated with the use of plasma from 198 patients with trypanosomiasis that was confirmed on parasitologic analysis and from 99 local controls with neither clinical nor serologic evidence of the disease. The specimens were collected in the Democratic Republic of Congo (4) and obtained from the World Health Organization HAT Specimen Bank (www.who.int/trypanosomiasis_african/research/en). All specimens were tested with the use of immune trypanolysis, the reference test for detecting specific antibodies against T. brucei gambiense variable antigen types LiTat 1.3 and LiTat 1.5.(5) To evaluate the applicability of these tests when blood was used, samples of reconstituted blood were prepared by adding plasma from patients with trypanosomiasis or from local controls to sedimented blood cells from a healthy donor.

Results are summarized in Table 1. As compared with the immune trypanolysis test, the HAT Sero-Strip showed excellent sensitivity, with specificity being slightly lower when plasma was tested (P=0.05). When reconstituted blood was tested, the sensitivity and specificity of the HAT Sero-Strip did not differ significantly from the sensitivity and specificity of immune trypanolysis (P>0.05 for both comparisons); for the HAT Sero-K-SeT, the sensitivity was lower than that of immune trypanolysis (P=0.01), but the specificity was not significantly different (P=0.32).

If further evaluation in the field confirms their diagnostic accuracy, we believe that the HAT Sero-K-SeT and the HAT Sero-Strip, with an estimated price of less than $2.50 each, may become valuable tools in the control of trypanosomiasis.

Büscher P. (Institute of Tropical Medecine), Gilleman Q. (Coris BioConcept), Lejon V. (Institute of Tropical Medecine)

References:

1. Simarro PP, Jannin J, Cattand P. Eliminating human African trypanosomiasis: where do we stand and what comes next? PLoS Med 2008;5(2):e55.

2. Magnus E, Vervoort T, Van Meirvenne N. A card-agglutination test with stained trypanosomes (C.A.T.T.) for the serological diagnosis of T.b. gambiense trypanosomiasis. Ann Soc Belg Med Trop 1978;58:169-76.

3. Büscher P, Draelants E, Magnus E, Vervoort T, Van Meirvenne N. An experimental latex agglutination test for antibody detection in human African trypanosomiasis. Ann Soc Belg Med Trop 1991;71:267-73.

4. Amin DN, Rottenberg ME, Thomsen AR, et al. Expression and role of CXCL10 during the encephalitic stage of experimental and clinical African trypanosomiasis. J Infect Dis 2009;200: 1556-65.

5. Van Meirvenne N, Magnus E, Büscher P. Evaluation of variant specific trypanolysis tests for serodiagnosis of human infections with Trypanosoma brucei gambiense. Acta Trop 1995;60:189-99.

Rapid diagnostic test for Clostridium difficile

New kit with strip device available by end of November

Reliability of GDH test is a prerequisite with two- and three-step algorithms for lab Diagnosis of Clostridium difficile. This new C. diff-Strip kit meets this requirement with very relevant performances. An evaluation carried out on 250 human stool specimens was compared to the bacterial culture test used for routine testing at a clinical laboratory (Belgium) and led to the following performances : reliability of 97.6%.

We’ll be pleased to present this new product during MEDICA trade show 2012. Do not hesitate to meet us there, booth 1F38 or to contact us from now at client.care@corisbio.com.

Best regards,

Coris BioConcept Team

Martina Hitzbleck¹ ,  Laetitia Avrain² ,  Valerie Smekens² ,  Robert D. Lovchik¹ ,  Pascal Mertens² and Emmanuel Delamarche¹

M. Hitzbleck et al.
Lab Chip, 2012, 12, 1972-1978

Abstract

Capillary-driven microfluidics are simple to use and provide the opportunity to perform fast biological assays with nanogram quantities of reagents and microliters of sample. Here we describe capillary soft valves (CSVs) as a simple-to-implement and -actuate approach for stopping liquids in capillary-driven microfluidics. CSVs are inserted between wettable microstructures and work to block liquids owing to a capillary pressure barrier of a few kPa. This barrier is suppressed by pressing down the soft cover of the CSV using, for example, the tip of a pen. CSVs comprise a hard layer (in silicon or polymer) with wettable microstructures and a soft cover made of poly(dimethylsiloxane) (PDMS) here. CSVs have a footprint as small as 0.6 mm². We illustrate how these valves work in the context of detecting DNA analytes. Specifically, a dsDNA target (997 bp PCR product, non-purified) was detected at concentrations of 20 and 200 nM in a sample volume of 0.7 μL and within 10 min. The assay includes melting of the dsDNA at 95 °C, annealing of a 30-base biotinylated probe at 50 °C, and intercalation of a fluorescent dye into the re-hybridized dsDNA at 25 °C. Actuation of the CSV allows the DNA target–probe–dye complexes to flow over 100 μm wide, streptavidin receptor lines. This work suggests that CSVs can fulfil the requirements set by complex assays, in which elevated temperatures and reaction with probes, dyes and capture species are needed. CSVs therefore greatly complement capillary-driven microfluidics without adding significant design, fabrication and actuation issues.

http://pubs.rsc.org/en/content/articlelanding/2012/lc/c2lc00015f

¹Coris BioConcept
²IBM Research GmbH

Diagnostic tests are now so routinely used that nobody can imagine diagnosing any pathology without processing a sample through a panel of different tests.

Most methods used are intended to help the practitioner in giving the appropriate diagnostic to administrate the most convenient treatment or to conduct other confirmatory testings.  Nevertheless, the main problem to face is still to consider if a test is convenient to detect a precise pathology. In other words, does the test of interest answer the main question regarding the pathology: is the sample positive or negative for it? And even, when a sample is detected as positive or negative, what about the confidence in the result ?

One must consider if a test is able to distinguish between diseased and healthy people or more scientifically speaking between true positives versus true negatives. Several parameters allow characterising a diagnostic test.  These are mainly the specificity, the sensitivity, and the positive (PPV) and negative (NPV) predictive values.

Specificity is defined as the proportion of true negative samples, as measured by a gold standard, which are so identified by the diagnostic test under study while sensitivity is defined as the proportion of true positive samples, as measured by a gold standard, which are identified as positive by the test under study. These two parameters are not linked to any prevalence of the disease since they are calculated on either negative sampling or positive sampling respectively which do not depend on the epidemiological status of the disease of interest.

Dependently of the disease, the test should be developed to be more sensitive or more specific and, by the way, to show either a high negative predictive value or a high positive predictive value. To this concern, Clostridium difficile diagnosis is a very good example. Most of the algorithms used in laboratories described a two steps methodology with a first test to identify the bacteria. This is to be carried out by the detection of the glutamate dehydrogenase enzyme, specific for C. difficile. If this test is positive, then toxins detection must be considered and performed either by immunological assays or, better, molecular assays.

In this case, because infected people are at high health risk and because any detected positive should give rise to other testings, both sensitivity and NPV should be as high as possible, to avoid useless testings. And the goal to reach for any test is to show 100 % NPV. By having such a high value, practioners know without any doubt that all the negatives are real negatives.

And what is claimed in hospital: “What we will be looking for is a rapid GDH test that has a high NPV to exclude those specimens where C.difficile is not present from the second more expensive and time consuming test for C.difficile toxin with the Vidas ».

And it is exactly what Coris is now proposing, indeed.

Clostridium difficile is one of the most prevalent nosocomial pathogen mainly affecting patients after antibiotic treatment. Toxinogenic strains of C. difficile cause infections from mild diarrhoea to pseudomembranous colitis, potentially leading to death. The tissue-damaging enterotoxin (Toxin A) and the cytotoxin (Toxin B) produced by toxinogenic strains of C.difficile are responsible for the disease.

Due to the lack of sensitivity of toxins A&B rapid diagnostic tests, recommended algorithms for testing for toxinogenic C. difficile infection require detection of the C. difficile GDH as antigenic marker in stool as a first step. This test should have the highest possible sensitivity to ensure that no infected patients are missed.

Coris BioConcept Clostridium K-SeT allows the specific detection of C.difficile‘s GDH in stool specimen. There is a 100% concordance for detection of GDH between the Clostridium K-SeT test and an ELISA assay.  Moreover, another study shows a 100% NPV regarding culture.  This evaluation has been conducted in a reference lab in Brussels and compared to a test regarded as the reference test in the EC and the US.

This study has shown that the Coris test performs better than the reference one. Results have been submitted at the ICAAC meeting in San Francisco this year.

Coris BioConcept has received the “Walloon Quality Award” based on the EFQM Excellence Model (European Foundation for Quality Management).

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